License cleanup: add SPDX GPL-2.0 license identifier to files with no license
Many source files in the tree are missing licensing information, which
makes it harder for compliance tools to determine the correct license.
By default all files without license information are under the default
license of the kernel, which is GPL version 2.
Update the files which contain no license information with the 'GPL-2.0'
SPDX license identifier. The SPDX identifier is a legally binding
shorthand, which can be used instead of the full boiler plate text.
This patch is based on work done by Thomas Gleixner and Kate Stewart and
Philippe Ombredanne.
How this work was done:
Patches were generated and checked against linux-4.14-rc6 for a subset of
the use cases:
- file had no licensing information it it.
- file was a */uapi/* one with no licensing information in it,
- file was a */uapi/* one with existing licensing information,
Further patches will be generated in subsequent months to fix up cases
where non-standard license headers were used, and references to license
had to be inferred by heuristics based on keywords.
The analysis to determine which SPDX License Identifier to be applied to
a file was done in a spreadsheet of side by side results from of the
output of two independent scanners (ScanCode & Windriver) producing SPDX
tag:value files created by Philippe Ombredanne. Philippe prepared the
base worksheet, and did an initial spot review of a few 1000 files.
The 4.13 kernel was the starting point of the analysis with 60,537 files
assessed. Kate Stewart did a file by file comparison of the scanner
results in the spreadsheet to determine which SPDX license identifier(s)
to be applied to the file. She confirmed any determination that was not
immediately clear with lawyers working with the Linux Foundation.
Criteria used to select files for SPDX license identifier tagging was:
- Files considered eligible had to be source code files.
- Make and config files were included as candidates if they contained >5
lines of source
- File already had some variant of a license header in it (even if <5
lines).
All documentation files were explicitly excluded.
The following heuristics were used to determine which SPDX license
identifiers to apply.
- when both scanners couldn't find any license traces, file was
considered to have no license information in it, and the top level
COPYING file license applied.
For non */uapi/* files that summary was:
SPDX license identifier # files
---------------------------------------------------|-------
GPL-2.0 11139
and resulted in the first patch in this series.
If that file was a */uapi/* path one, it was "GPL-2.0 WITH
Linux-syscall-note" otherwise it was "GPL-2.0". Results of that was:
SPDX license identifier # files
---------------------------------------------------|-------
GPL-2.0 WITH Linux-syscall-note 930
and resulted in the second patch in this series.
- if a file had some form of licensing information in it, and was one
of the */uapi/* ones, it was denoted with the Linux-syscall-note if
any GPL family license was found in the file or had no licensing in
it (per prior point). Results summary:
SPDX license identifier # files
---------------------------------------------------|------
GPL-2.0 WITH Linux-syscall-note 270
GPL-2.0+ WITH Linux-syscall-note 169
((GPL-2.0 WITH Linux-syscall-note) OR BSD-2-Clause) 21
((GPL-2.0 WITH Linux-syscall-note) OR BSD-3-Clause) 17
LGPL-2.1+ WITH Linux-syscall-note 15
GPL-1.0+ WITH Linux-syscall-note 14
((GPL-2.0+ WITH Linux-syscall-note) OR BSD-3-Clause) 5
LGPL-2.0+ WITH Linux-syscall-note 4
LGPL-2.1 WITH Linux-syscall-note 3
((GPL-2.0 WITH Linux-syscall-note) OR MIT) 3
((GPL-2.0 WITH Linux-syscall-note) AND MIT) 1
and that resulted in the third patch in this series.
- when the two scanners agreed on the detected license(s), that became
the concluded license(s).
- when there was disagreement between the two scanners (one detected a
license but the other didn't, or they both detected different
licenses) a manual inspection of the file occurred.
- In most cases a manual inspection of the information in the file
resulted in a clear resolution of the license that should apply (and
which scanner probably needed to revisit its heuristics).
- When it was not immediately clear, the license identifier was
confirmed with lawyers working with the Linux Foundation.
- If there was any question as to the appropriate license identifier,
the file was flagged for further research and to be revisited later
in time.
In total, over 70 hours of logged manual review was done on the
spreadsheet to determine the SPDX license identifiers to apply to the
source files by Kate, Philippe, Thomas and, in some cases, confirmation
by lawyers working with the Linux Foundation.
Kate also obtained a third independent scan of the 4.13 code base from
FOSSology, and compared selected files where the other two scanners
disagreed against that SPDX file, to see if there was new insights. The
Windriver scanner is based on an older version of FOSSology in part, so
they are related.
Thomas did random spot checks in about 500 files from the spreadsheets
for the uapi headers and agreed with SPDX license identifier in the
files he inspected. For the non-uapi files Thomas did random spot checks
in about 15000 files.
In initial set of patches against 4.14-rc6, 3 files were found to have
copy/paste license identifier errors, and have been fixed to reflect the
correct identifier.
Additionally Philippe spent 10 hours this week doing a detailed manual
inspection and review of the 12,461 patched files from the initial patch
version early this week with:
- a full scancode scan run, collecting the matched texts, detected
license ids and scores
- reviewing anything where there was a license detected (about 500+
files) to ensure that the applied SPDX license was correct
- reviewing anything where there was no detection but the patch license
was not GPL-2.0 WITH Linux-syscall-note to ensure that the applied
SPDX license was correct
This produced a worksheet with 20 files needing minor correction. This
worksheet was then exported into 3 different .csv files for the
different types of files to be modified.
These .csv files were then reviewed by Greg. Thomas wrote a script to
parse the csv files and add the proper SPDX tag to the file, in the
format that the file expected. This script was further refined by Greg
based on the output to detect more types of files automatically and to
distinguish between header and source .c files (which need different
comment types.) Finally Greg ran the script using the .csv files to
generate the patches.
Reviewed-by: Kate Stewart <kstewart@linuxfoundation.org>
Reviewed-by: Philippe Ombredanne <pombredanne@nexb.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2017-11-01 14:07:57 +00:00
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// SPDX-License-Identifier: GPL-2.0
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2007-07-09 16:51:58 +00:00
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/*
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* Real-Time Scheduling Class (mapped to the SCHED_FIFO and SCHED_RR
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* policies)
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*/
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2018-06-28 15:45:05 +00:00
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2013-02-07 15:47:04 +00:00
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int sched_rr_timeslice = RR_TIMESLICE;
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2020-04-25 10:52:48 +00:00
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/* More than 4 hours if BW_SHIFT equals 20. */
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static const u64 max_rt_runtime = MAX_BW;
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2013-02-07 15:47:04 +00:00
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2011-10-25 08:00:11 +00:00
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static int do_sched_rt_period_timer(struct rt_bandwidth *rt_b, int overrun);
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struct rt_bandwidth def_rt_bandwidth;
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2022-02-15 11:45:59 +00:00
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/*
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* period over which we measure -rt task CPU usage in us.
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* default: 1s
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*/
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unsigned int sysctl_sched_rt_period = 1000000;
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/*
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* part of the period that we allow rt tasks to run in us.
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* default: 0.95s
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*/
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int sysctl_sched_rt_runtime = 950000;
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2022-03-18 02:54:17 +00:00
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#ifdef CONFIG_SYSCTL
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static int sysctl_sched_rr_timeslice = (MSEC_PER_SEC / HZ) * RR_TIMESLICE;
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2022-02-15 11:45:59 +00:00
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static int sched_rt_handler(struct ctl_table *table, int write, void *buffer,
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size_t *lenp, loff_t *ppos);
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2022-02-15 11:46:01 +00:00
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static int sched_rr_handler(struct ctl_table *table, int write, void *buffer,
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size_t *lenp, loff_t *ppos);
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2022-02-15 11:45:59 +00:00
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static struct ctl_table sched_rt_sysctls[] = {
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{
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.procname = "sched_rt_period_us",
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.data = &sysctl_sched_rt_period,
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.maxlen = sizeof(unsigned int),
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.mode = 0644,
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.proc_handler = sched_rt_handler,
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},
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{
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.procname = "sched_rt_runtime_us",
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.data = &sysctl_sched_rt_runtime,
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.maxlen = sizeof(int),
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.mode = 0644,
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.proc_handler = sched_rt_handler,
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},
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2022-02-15 11:46:01 +00:00
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{
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.procname = "sched_rr_timeslice_ms",
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.data = &sysctl_sched_rr_timeslice,
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.maxlen = sizeof(int),
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.mode = 0644,
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.proc_handler = sched_rr_handler,
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},
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2022-02-15 11:45:59 +00:00
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{}
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};
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static int __init sched_rt_sysctl_init(void)
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{
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register_sysctl_init("kernel", sched_rt_sysctls);
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return 0;
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}
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late_initcall(sched_rt_sysctl_init);
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#endif
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2011-10-25 08:00:11 +00:00
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static enum hrtimer_restart sched_rt_period_timer(struct hrtimer *timer)
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{
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struct rt_bandwidth *rt_b =
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container_of(timer, struct rt_bandwidth, rt_period_timer);
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int idle = 0;
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sched: Cleanup bandwidth timers
Roman reported a 3 cpu lockup scenario involving __start_cfs_bandwidth().
The more I look at that code the more I'm convinced its crack, that
entire __start_cfs_bandwidth() thing is brain melting, we don't need to
cancel a timer before starting it, *hrtimer_start*() will happily remove
the timer for you if its still enqueued.
Removing that, removes a big part of the problem, no more ugly cancel
loop to get stuck in.
So now, if I understand things right, the entire reason you have this
cfs_b->lock guarded ->timer_active nonsense is to make sure we don't
accidentally lose the timer.
It appears to me that it should be possible to guarantee that same by
unconditionally (re)starting the timer when !queued. Because regardless
what hrtimer::function will return, if we beat it to (re)enqueue the
timer, it doesn't matter.
Now, because hrtimers don't come with any serialization guarantees we
must ensure both handler and (re)start loop serialize their access to
the hrtimer to avoid both trying to forward the timer at the same
time.
Update the rt bandwidth timer to match.
This effectively reverts: 09dc4ab03936 ("sched/fair: Fix
tg_set_cfs_bandwidth() deadlock on rq->lock").
Reported-by: Roman Gushchin <klamm@yandex-team.ru>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Ben Segall <bsegall@google.com>
Cc: Paul Turner <pjt@google.com>
Link: http://lkml.kernel.org/r/20150415095011.804589208@infradead.org
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
2015-04-15 09:41:57 +00:00
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int overrun;
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2011-10-25 08:00:11 +00:00
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sched: Cleanup bandwidth timers
Roman reported a 3 cpu lockup scenario involving __start_cfs_bandwidth().
The more I look at that code the more I'm convinced its crack, that
entire __start_cfs_bandwidth() thing is brain melting, we don't need to
cancel a timer before starting it, *hrtimer_start*() will happily remove
the timer for you if its still enqueued.
Removing that, removes a big part of the problem, no more ugly cancel
loop to get stuck in.
So now, if I understand things right, the entire reason you have this
cfs_b->lock guarded ->timer_active nonsense is to make sure we don't
accidentally lose the timer.
It appears to me that it should be possible to guarantee that same by
unconditionally (re)starting the timer when !queued. Because regardless
what hrtimer::function will return, if we beat it to (re)enqueue the
timer, it doesn't matter.
Now, because hrtimers don't come with any serialization guarantees we
must ensure both handler and (re)start loop serialize their access to
the hrtimer to avoid both trying to forward the timer at the same
time.
Update the rt bandwidth timer to match.
This effectively reverts: 09dc4ab03936 ("sched/fair: Fix
tg_set_cfs_bandwidth() deadlock on rq->lock").
Reported-by: Roman Gushchin <klamm@yandex-team.ru>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Ben Segall <bsegall@google.com>
Cc: Paul Turner <pjt@google.com>
Link: http://lkml.kernel.org/r/20150415095011.804589208@infradead.org
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
2015-04-15 09:41:57 +00:00
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raw_spin_lock(&rt_b->rt_runtime_lock);
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2011-10-25 08:00:11 +00:00
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for (;;) {
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sched: Cleanup bandwidth timers
Roman reported a 3 cpu lockup scenario involving __start_cfs_bandwidth().
The more I look at that code the more I'm convinced its crack, that
entire __start_cfs_bandwidth() thing is brain melting, we don't need to
cancel a timer before starting it, *hrtimer_start*() will happily remove
the timer for you if its still enqueued.
Removing that, removes a big part of the problem, no more ugly cancel
loop to get stuck in.
So now, if I understand things right, the entire reason you have this
cfs_b->lock guarded ->timer_active nonsense is to make sure we don't
accidentally lose the timer.
It appears to me that it should be possible to guarantee that same by
unconditionally (re)starting the timer when !queued. Because regardless
what hrtimer::function will return, if we beat it to (re)enqueue the
timer, it doesn't matter.
Now, because hrtimers don't come with any serialization guarantees we
must ensure both handler and (re)start loop serialize their access to
the hrtimer to avoid both trying to forward the timer at the same
time.
Update the rt bandwidth timer to match.
This effectively reverts: 09dc4ab03936 ("sched/fair: Fix
tg_set_cfs_bandwidth() deadlock on rq->lock").
Reported-by: Roman Gushchin <klamm@yandex-team.ru>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Ben Segall <bsegall@google.com>
Cc: Paul Turner <pjt@google.com>
Link: http://lkml.kernel.org/r/20150415095011.804589208@infradead.org
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
2015-04-15 09:41:57 +00:00
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overrun = hrtimer_forward_now(timer, rt_b->rt_period);
|
2011-10-25 08:00:11 +00:00
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if (!overrun)
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break;
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|
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|
sched: Cleanup bandwidth timers
Roman reported a 3 cpu lockup scenario involving __start_cfs_bandwidth().
The more I look at that code the more I'm convinced its crack, that
entire __start_cfs_bandwidth() thing is brain melting, we don't need to
cancel a timer before starting it, *hrtimer_start*() will happily remove
the timer for you if its still enqueued.
Removing that, removes a big part of the problem, no more ugly cancel
loop to get stuck in.
So now, if I understand things right, the entire reason you have this
cfs_b->lock guarded ->timer_active nonsense is to make sure we don't
accidentally lose the timer.
It appears to me that it should be possible to guarantee that same by
unconditionally (re)starting the timer when !queued. Because regardless
what hrtimer::function will return, if we beat it to (re)enqueue the
timer, it doesn't matter.
Now, because hrtimers don't come with any serialization guarantees we
must ensure both handler and (re)start loop serialize their access to
the hrtimer to avoid both trying to forward the timer at the same
time.
Update the rt bandwidth timer to match.
This effectively reverts: 09dc4ab03936 ("sched/fair: Fix
tg_set_cfs_bandwidth() deadlock on rq->lock").
Reported-by: Roman Gushchin <klamm@yandex-team.ru>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Ben Segall <bsegall@google.com>
Cc: Paul Turner <pjt@google.com>
Link: http://lkml.kernel.org/r/20150415095011.804589208@infradead.org
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
2015-04-15 09:41:57 +00:00
|
|
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raw_spin_unlock(&rt_b->rt_runtime_lock);
|
2011-10-25 08:00:11 +00:00
|
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idle = do_sched_rt_period_timer(rt_b, overrun);
|
sched: Cleanup bandwidth timers
Roman reported a 3 cpu lockup scenario involving __start_cfs_bandwidth().
The more I look at that code the more I'm convinced its crack, that
entire __start_cfs_bandwidth() thing is brain melting, we don't need to
cancel a timer before starting it, *hrtimer_start*() will happily remove
the timer for you if its still enqueued.
Removing that, removes a big part of the problem, no more ugly cancel
loop to get stuck in.
So now, if I understand things right, the entire reason you have this
cfs_b->lock guarded ->timer_active nonsense is to make sure we don't
accidentally lose the timer.
It appears to me that it should be possible to guarantee that same by
unconditionally (re)starting the timer when !queued. Because regardless
what hrtimer::function will return, if we beat it to (re)enqueue the
timer, it doesn't matter.
Now, because hrtimers don't come with any serialization guarantees we
must ensure both handler and (re)start loop serialize their access to
the hrtimer to avoid both trying to forward the timer at the same
time.
Update the rt bandwidth timer to match.
This effectively reverts: 09dc4ab03936 ("sched/fair: Fix
tg_set_cfs_bandwidth() deadlock on rq->lock").
Reported-by: Roman Gushchin <klamm@yandex-team.ru>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Ben Segall <bsegall@google.com>
Cc: Paul Turner <pjt@google.com>
Link: http://lkml.kernel.org/r/20150415095011.804589208@infradead.org
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
2015-04-15 09:41:57 +00:00
|
|
|
raw_spin_lock(&rt_b->rt_runtime_lock);
|
2011-10-25 08:00:11 +00:00
|
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}
|
sched,perf: Fix periodic timers
In the below two commits (see Fixes) we have periodic timers that can
stop themselves when they're no longer required, but need to be
(re)-started when their idle condition changes.
Further complications is that we want the timer handler to always do
the forward such that it will always correctly deal with the overruns,
and we do not want to race such that the handler has already decided
to stop, but the (external) restart sees the timer still active and we
end up with a 'lost' timer.
The problem with the current code is that the re-start can come before
the callback does the forward, at which point the forward from the
callback will WARN about forwarding an enqueued timer.
Now, conceptually its easy to detect if you're before or after the fwd
by comparing the expiration time against the current time. Of course,
that's expensive (and racy) because we don't have the current time.
Alternatively one could cache this state inside the timer, but then
everybody pays the overhead of maintaining this extra state, and that
is undesired.
The only other option that I could see is the external timer_active
variable, which I tried to kill before. I would love a nicer interface
for this seemingly simple 'problem' but alas.
Fixes: 272325c4821f ("perf: Fix mux_interval hrtimer wreckage")
Fixes: 77a4d1a1b9a1 ("sched: Cleanup bandwidth timers")
Cc: pjt@google.com
Cc: tglx@linutronix.de
Cc: klamm@yandex-team.ru
Cc: mingo@kernel.org
Cc: bsegall@google.com
Cc: hpa@zytor.com
Cc: Sasha Levin <sasha.levin@oracle.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20150514102311.GX21418@twins.programming.kicks-ass.net
2015-05-14 10:23:11 +00:00
|
|
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if (idle)
|
|
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rt_b->rt_period_active = 0;
|
sched: Cleanup bandwidth timers
Roman reported a 3 cpu lockup scenario involving __start_cfs_bandwidth().
The more I look at that code the more I'm convinced its crack, that
entire __start_cfs_bandwidth() thing is brain melting, we don't need to
cancel a timer before starting it, *hrtimer_start*() will happily remove
the timer for you if its still enqueued.
Removing that, removes a big part of the problem, no more ugly cancel
loop to get stuck in.
So now, if I understand things right, the entire reason you have this
cfs_b->lock guarded ->timer_active nonsense is to make sure we don't
accidentally lose the timer.
It appears to me that it should be possible to guarantee that same by
unconditionally (re)starting the timer when !queued. Because regardless
what hrtimer::function will return, if we beat it to (re)enqueue the
timer, it doesn't matter.
Now, because hrtimers don't come with any serialization guarantees we
must ensure both handler and (re)start loop serialize their access to
the hrtimer to avoid both trying to forward the timer at the same
time.
Update the rt bandwidth timer to match.
This effectively reverts: 09dc4ab03936 ("sched/fair: Fix
tg_set_cfs_bandwidth() deadlock on rq->lock").
Reported-by: Roman Gushchin <klamm@yandex-team.ru>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Ben Segall <bsegall@google.com>
Cc: Paul Turner <pjt@google.com>
Link: http://lkml.kernel.org/r/20150415095011.804589208@infradead.org
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
2015-04-15 09:41:57 +00:00
|
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raw_spin_unlock(&rt_b->rt_runtime_lock);
|
2011-10-25 08:00:11 +00:00
|
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return idle ? HRTIMER_NORESTART : HRTIMER_RESTART;
|
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}
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void init_rt_bandwidth(struct rt_bandwidth *rt_b, u64 period, u64 runtime)
|
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{
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rt_b->rt_period = ns_to_ktime(period);
|
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rt_b->rt_runtime = runtime;
|
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raw_spin_lock_init(&rt_b->rt_runtime_lock);
|
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|
2019-07-26 18:30:52 +00:00
|
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hrtimer_init(&rt_b->rt_period_timer, CLOCK_MONOTONIC,
|
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HRTIMER_MODE_REL_HARD);
|
2011-10-25 08:00:11 +00:00
|
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rt_b->rt_period_timer.function = sched_rt_period_timer;
|
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}
|
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|
2021-12-03 03:36:18 +00:00
|
|
|
static inline void do_start_rt_bandwidth(struct rt_bandwidth *rt_b)
|
2011-10-25 08:00:11 +00:00
|
|
|
{
|
|
|
|
raw_spin_lock(&rt_b->rt_runtime_lock);
|
sched,perf: Fix periodic timers
In the below two commits (see Fixes) we have periodic timers that can
stop themselves when they're no longer required, but need to be
(re)-started when their idle condition changes.
Further complications is that we want the timer handler to always do
the forward such that it will always correctly deal with the overruns,
and we do not want to race such that the handler has already decided
to stop, but the (external) restart sees the timer still active and we
end up with a 'lost' timer.
The problem with the current code is that the re-start can come before
the callback does the forward, at which point the forward from the
callback will WARN about forwarding an enqueued timer.
Now, conceptually its easy to detect if you're before or after the fwd
by comparing the expiration time against the current time. Of course,
that's expensive (and racy) because we don't have the current time.
Alternatively one could cache this state inside the timer, but then
everybody pays the overhead of maintaining this extra state, and that
is undesired.
The only other option that I could see is the external timer_active
variable, which I tried to kill before. I would love a nicer interface
for this seemingly simple 'problem' but alas.
Fixes: 272325c4821f ("perf: Fix mux_interval hrtimer wreckage")
Fixes: 77a4d1a1b9a1 ("sched: Cleanup bandwidth timers")
Cc: pjt@google.com
Cc: tglx@linutronix.de
Cc: klamm@yandex-team.ru
Cc: mingo@kernel.org
Cc: bsegall@google.com
Cc: hpa@zytor.com
Cc: Sasha Levin <sasha.levin@oracle.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20150514102311.GX21418@twins.programming.kicks-ass.net
2015-05-14 10:23:11 +00:00
|
|
|
if (!rt_b->rt_period_active) {
|
|
|
|
rt_b->rt_period_active = 1;
|
sched/rt: Kick RT bandwidth timer immediately on start up
I've been debugging why deadline tasks can cause the RT scheduler to
throttle, even when the deadline tasks are only taking up 50% of the
CPU and RT tasks are not even using 1% of the CPU. Here's what I found.
In order to keep a CPU from being hogged by RT tasks, the deadline
scheduler adds its run time (delta_exec) to the rt_time of the RT
bandwidth. That way, if the two use more than 95% of the CPU within one
second (default settings), the RT tasks are throttled to allow non RT
tasks to run.
Although the deadline tasks add their run time to the RT bandwidth, it
lets the RT tasks do the accounting. This is where the problem lies. If
a deadline task runs for a bit, and no RT tasks are running, then it
will continually add to the RT rt_time that is used to calculate how
much CPU the RT tasks use. But no RT period is in play, and this
accumulation of the runtime never gets reset.
When an RT task finally gets to run, and the watchdog goes off, it can
see that the RT task has used more than it should of, because the
deadline task added all this runtime to its rt_time. Then the RT task
that just woke up gets throttled for no good reason.
I also noticed that when an RT task is queued, it starts the timer to
account for overload and such. But that timer goes off one period
later, which may be too late and the extra rt_time will trigger a
throttle.
This is a quick work around to the problem. When a new RT task is
queued, the bandwidth timer is set to go off immediately. Then the
timer can clear out the extra time added to the rt_time while there was
no RT task running. This stops my tests from triggering the throttle,
and it will still throttle if an RT task runs too much, even while a
deadline task is running.
A better solution may be to subtract the bandwidth that the deadline
task uses from the rt_runtime, and add it back when its finished. Then
there wont be a need for runtime tracking of the time used by deadline
tasks.
I may play with that solution tomorrow.
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: <juri.lelli@gmail.com>
Cc: <williams@redhat.com>
Cc: Clark Williams
Cc: Daniel Bristot de Oliveira <bristot@redhat.com>
Cc: John Kacur <jkacur@redhat.com>
Cc: Juri Lelli
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20160216183746.349ec98b@gandalf.local.home
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2016-02-16 23:37:46 +00:00
|
|
|
/*
|
|
|
|
* SCHED_DEADLINE updates the bandwidth, as a run away
|
|
|
|
* RT task with a DL task could hog a CPU. But DL does
|
|
|
|
* not reset the period. If a deadline task was running
|
|
|
|
* without an RT task running, it can cause RT tasks to
|
|
|
|
* throttle when they start up. Kick the timer right away
|
|
|
|
* to update the period.
|
|
|
|
*/
|
|
|
|
hrtimer_forward_now(&rt_b->rt_period_timer, ns_to_ktime(0));
|
2019-07-26 18:30:52 +00:00
|
|
|
hrtimer_start_expires(&rt_b->rt_period_timer,
|
|
|
|
HRTIMER_MODE_ABS_PINNED_HARD);
|
sched,perf: Fix periodic timers
In the below two commits (see Fixes) we have periodic timers that can
stop themselves when they're no longer required, but need to be
(re)-started when their idle condition changes.
Further complications is that we want the timer handler to always do
the forward such that it will always correctly deal with the overruns,
and we do not want to race such that the handler has already decided
to stop, but the (external) restart sees the timer still active and we
end up with a 'lost' timer.
The problem with the current code is that the re-start can come before
the callback does the forward, at which point the forward from the
callback will WARN about forwarding an enqueued timer.
Now, conceptually its easy to detect if you're before or after the fwd
by comparing the expiration time against the current time. Of course,
that's expensive (and racy) because we don't have the current time.
Alternatively one could cache this state inside the timer, but then
everybody pays the overhead of maintaining this extra state, and that
is undesired.
The only other option that I could see is the external timer_active
variable, which I tried to kill before. I would love a nicer interface
for this seemingly simple 'problem' but alas.
Fixes: 272325c4821f ("perf: Fix mux_interval hrtimer wreckage")
Fixes: 77a4d1a1b9a1 ("sched: Cleanup bandwidth timers")
Cc: pjt@google.com
Cc: tglx@linutronix.de
Cc: klamm@yandex-team.ru
Cc: mingo@kernel.org
Cc: bsegall@google.com
Cc: hpa@zytor.com
Cc: Sasha Levin <sasha.levin@oracle.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20150514102311.GX21418@twins.programming.kicks-ass.net
2015-05-14 10:23:11 +00:00
|
|
|
}
|
2011-10-25 08:00:11 +00:00
|
|
|
raw_spin_unlock(&rt_b->rt_runtime_lock);
|
|
|
|
}
|
|
|
|
|
2021-12-03 03:36:18 +00:00
|
|
|
static void start_rt_bandwidth(struct rt_bandwidth *rt_b)
|
|
|
|
{
|
|
|
|
if (!rt_bandwidth_enabled() || rt_b->rt_runtime == RUNTIME_INF)
|
|
|
|
return;
|
|
|
|
|
|
|
|
do_start_rt_bandwidth(rt_b);
|
|
|
|
}
|
|
|
|
|
2015-03-03 11:50:27 +00:00
|
|
|
void init_rt_rq(struct rt_rq *rt_rq)
|
2011-10-25 08:00:11 +00:00
|
|
|
{
|
|
|
|
struct rt_prio_array *array;
|
|
|
|
int i;
|
|
|
|
|
|
|
|
array = &rt_rq->active;
|
|
|
|
for (i = 0; i < MAX_RT_PRIO; i++) {
|
|
|
|
INIT_LIST_HEAD(array->queue + i);
|
|
|
|
__clear_bit(i, array->bitmap);
|
|
|
|
}
|
|
|
|
/* delimiter for bitsearch: */
|
|
|
|
__set_bit(MAX_RT_PRIO, array->bitmap);
|
|
|
|
|
|
|
|
#if defined CONFIG_SMP
|
2020-10-14 19:06:49 +00:00
|
|
|
rt_rq->highest_prio.curr = MAX_RT_PRIO-1;
|
|
|
|
rt_rq->highest_prio.next = MAX_RT_PRIO-1;
|
2011-10-25 08:00:11 +00:00
|
|
|
rt_rq->rt_nr_migratory = 0;
|
|
|
|
rt_rq->overloaded = 0;
|
|
|
|
plist_head_init(&rt_rq->pushable_tasks);
|
sched/rt: Use IPI to trigger RT task push migration instead of pulling
When debugging the latencies on a 40 core box, where we hit 300 to
500 microsecond latencies, I found there was a huge contention on the
runqueue locks.
Investigating it further, running ftrace, I found that it was due to
the pulling of RT tasks.
The test that was run was the following:
cyclictest --numa -p95 -m -d0 -i100
This created a thread on each CPU, that would set its wakeup in iterations
of 100 microseconds. The -d0 means that all the threads had the same
interval (100us). Each thread sleeps for 100us and wakes up and measures
its latencies.
cyclictest is maintained at:
git://git.kernel.org/pub/scm/linux/kernel/git/clrkwllms/rt-tests.git
What happened was another RT task would be scheduled on one of the CPUs
that was running our test, when the other CPU tests went to sleep and
scheduled idle. This caused the "pull" operation to execute on all
these CPUs. Each one of these saw the RT task that was overloaded on
the CPU of the test that was still running, and each one tried
to grab that task in a thundering herd way.
To grab the task, each thread would do a double rq lock grab, grabbing
its own lock as well as the rq of the overloaded CPU. As the sched
domains on this box was rather flat for its size, I saw up to 12 CPUs
block on this lock at once. This caused a ripple affect with the
rq locks especially since the taking was done via a double rq lock, which
means that several of the CPUs had their own rq locks held while trying
to take this rq lock. As these locks were blocked, any wakeups or load
balanceing on these CPUs would also block on these locks, and the wait
time escalated.
I've tried various methods to lessen the load, but things like an
atomic counter to only let one CPU grab the task wont work, because
the task may have a limited affinity, and we may pick the wrong
CPU to take that lock and do the pull, to only find out that the
CPU we picked isn't in the task's affinity.
Instead of doing the PULL, I now have the CPUs that want the pull to
send over an IPI to the overloaded CPU, and let that CPU pick what
CPU to push the task to. No more need to grab the rq lock, and the
push/pull algorithm still works fine.
With this patch, the latency dropped to just 150us over a 20 hour run.
Without the patch, the huge latencies would trigger in seconds.
I've created a new sched feature called RT_PUSH_IPI, which is enabled
by default.
When RT_PUSH_IPI is not enabled, the old method of grabbing the rq locks
and having the pulling CPU do the work is implemented. When RT_PUSH_IPI
is enabled, the IPI is sent to the overloaded CPU to do a push.
To enabled or disable this at run time:
# mount -t debugfs nodev /sys/kernel/debug
# echo RT_PUSH_IPI > /sys/kernel/debug/sched_features
or
# echo NO_RT_PUSH_IPI > /sys/kernel/debug/sched_features
Update: This original patch would send an IPI to all CPUs in the RT overload
list. But that could theoretically cause the reverse issue. That is, there
could be lots of overloaded RT queues and one CPU lowers its priority. It would
then send an IPI to all the overloaded RT queues and they could then all try
to grab the rq lock of the CPU lowering its priority, and then we have the
same problem.
The latest design sends out only one IPI to the first overloaded CPU. It tries to
push any tasks that it can, and then looks for the next overloaded CPU that can
push to the source CPU. The IPIs stop when all overloaded CPUs that have pushable
tasks that have priorities greater than the source CPU are covered. In case the
source CPU lowers its priority again, a flag is set to tell the IPI traversal to
restart with the first RT overloaded CPU after the source CPU.
Parts-suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Joern Engel <joern@purestorage.com>
Cc: Clark Williams <williams@redhat.com>
Cc: Mike Galbraith <umgwanakikbuti@gmail.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20150318144946.2f3cc982@gandalf.local.home
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2015-03-18 18:49:46 +00:00
|
|
|
#endif /* CONFIG_SMP */
|
2014-03-14 22:15:00 +00:00
|
|
|
/* We start is dequeued state, because no RT tasks are queued */
|
|
|
|
rt_rq->rt_queued = 0;
|
2011-10-25 08:00:11 +00:00
|
|
|
|
|
|
|
rt_rq->rt_time = 0;
|
|
|
|
rt_rq->rt_throttled = 0;
|
|
|
|
rt_rq->rt_runtime = 0;
|
|
|
|
raw_spin_lock_init(&rt_rq->rt_runtime_lock);
|
|
|
|
}
|
|
|
|
|
2009-07-24 10:25:30 +00:00
|
|
|
#ifdef CONFIG_RT_GROUP_SCHED
|
2011-10-25 08:00:11 +00:00
|
|
|
static void destroy_rt_bandwidth(struct rt_bandwidth *rt_b)
|
|
|
|
{
|
|
|
|
hrtimer_cancel(&rt_b->rt_period_timer);
|
|
|
|
}
|
2009-07-24 10:25:30 +00:00
|
|
|
|
|
|
|
#define rt_entity_is_task(rt_se) (!(rt_se)->my_q)
|
|
|
|
|
2009-01-14 14:10:04 +00:00
|
|
|
static inline struct task_struct *rt_task_of(struct sched_rt_entity *rt_se)
|
|
|
|
{
|
2009-07-24 10:25:30 +00:00
|
|
|
#ifdef CONFIG_SCHED_DEBUG
|
|
|
|
WARN_ON_ONCE(!rt_entity_is_task(rt_se));
|
|
|
|
#endif
|
2009-01-14 14:10:04 +00:00
|
|
|
return container_of(rt_se, struct task_struct, rt);
|
|
|
|
}
|
|
|
|
|
|
|
|
static inline struct rq *rq_of_rt_rq(struct rt_rq *rt_rq)
|
|
|
|
{
|
|
|
|
return rt_rq->rq;
|
|
|
|
}
|
|
|
|
|
|
|
|
static inline struct rt_rq *rt_rq_of_se(struct sched_rt_entity *rt_se)
|
|
|
|
{
|
|
|
|
return rt_se->rt_rq;
|
|
|
|
}
|
|
|
|
|
2014-03-14 22:14:55 +00:00
|
|
|
static inline struct rq *rq_of_rt_se(struct sched_rt_entity *rt_se)
|
|
|
|
{
|
|
|
|
struct rt_rq *rt_rq = rt_se->rt_rq;
|
|
|
|
|
|
|
|
return rt_rq->rq;
|
|
|
|
}
|
|
|
|
|
sched/fair: Prevent dead task groups from regaining cfs_rq's
Kevin is reporting crashes which point to a use-after-free of a cfs_rq
in update_blocked_averages(). Initial debugging revealed that we've
live cfs_rq's (on_list=1) in an about to be kfree()'d task group in
free_fair_sched_group(). However, it was unclear how that can happen.
His kernel config happened to lead to a layout of struct sched_entity
that put the 'my_q' member directly into the middle of the object
which makes it incidentally overlap with SLUB's freelist pointer.
That, in combination with SLAB_FREELIST_HARDENED's freelist pointer
mangling, leads to a reliable access violation in form of a #GP which
made the UAF fail fast.
Michal seems to have run into the same issue[1]. He already correctly
diagnosed that commit a7b359fc6a37 ("sched/fair: Correctly insert
cfs_rq's to list on unthrottle") is causing the preconditions for the
UAF to happen by re-adding cfs_rq's also to task groups that have no
more running tasks, i.e. also to dead ones. His analysis, however,
misses the real root cause and it cannot be seen from the crash
backtrace only, as the real offender is tg_unthrottle_up() getting
called via sched_cfs_period_timer() via the timer interrupt at an
inconvenient time.
When unregister_fair_sched_group() unlinks all cfs_rq's from the dying
task group, it doesn't protect itself from getting interrupted. If the
timer interrupt triggers while we iterate over all CPUs or after
unregister_fair_sched_group() has finished but prior to unlinking the
task group, sched_cfs_period_timer() will execute and walk the list of
task groups, trying to unthrottle cfs_rq's, i.e. re-add them to the
dying task group. These will later -- in free_fair_sched_group() -- be
kfree()'ed while still being linked, leading to the fireworks Kevin
and Michal are seeing.
To fix this race, ensure the dying task group gets unlinked first.
However, simply switching the order of unregistering and unlinking the
task group isn't sufficient, as concurrent RCU walkers might still see
it, as can be seen below:
CPU1: CPU2:
: timer IRQ:
: do_sched_cfs_period_timer():
: :
: distribute_cfs_runtime():
: rcu_read_lock();
: :
: unthrottle_cfs_rq():
sched_offline_group(): :
: walk_tg_tree_from(…,tg_unthrottle_up,…):
list_del_rcu(&tg->list); :
(1) : list_for_each_entry_rcu(child, &parent->children, siblings)
: :
(2) list_del_rcu(&tg->siblings); :
: tg_unthrottle_up():
unregister_fair_sched_group(): struct cfs_rq *cfs_rq = tg->cfs_rq[cpu_of(rq)];
: :
list_del_leaf_cfs_rq(tg->cfs_rq[cpu]); :
: :
: if (!cfs_rq_is_decayed(cfs_rq) || cfs_rq->nr_running)
(3) : list_add_leaf_cfs_rq(cfs_rq);
: :
: :
: :
: :
: :
(4) : rcu_read_unlock();
CPU 2 walks the task group list in parallel to sched_offline_group(),
specifically, it'll read the soon to be unlinked task group entry at
(1). Unlinking it on CPU 1 at (2) therefore won't prevent CPU 2 from
still passing it on to tg_unthrottle_up(). CPU 1 now tries to unlink
all cfs_rq's via list_del_leaf_cfs_rq() in
unregister_fair_sched_group(). Meanwhile CPU 2 will re-add some of
these at (3), which is the cause of the UAF later on.
To prevent this additional race from happening, we need to wait until
walk_tg_tree_from() has finished traversing the task groups, i.e.
after the RCU read critical section ends in (4). Afterwards we're safe
to call unregister_fair_sched_group(), as each new walk won't see the
dying task group any more.
On top of that, we need to wait yet another RCU grace period after
unregister_fair_sched_group() to ensure print_cfs_stats(), which might
run concurrently, always sees valid objects, i.e. not already free'd
ones.
This patch survives Michal's reproducer[2] for 8h+ now, which used to
trigger within minutes before.
[1] https://lore.kernel.org/lkml/20211011172236.11223-1-mkoutny@suse.com/
[2] https://lore.kernel.org/lkml/20211102160228.GA57072@blackbody.suse.cz/
Fixes: a7b359fc6a37 ("sched/fair: Correctly insert cfs_rq's to list on unthrottle")
[peterz: shuffle code around a bit]
Reported-by: Kevin Tanguy <kevin.tanguy@corp.ovh.com>
Signed-off-by: Mathias Krause <minipli@grsecurity.net>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
2021-11-03 19:06:13 +00:00
|
|
|
void unregister_rt_sched_group(struct task_group *tg)
|
2011-10-25 08:00:11 +00:00
|
|
|
{
|
|
|
|
if (tg->rt_se)
|
|
|
|
destroy_rt_bandwidth(&tg->rt_bandwidth);
|
|
|
|
|
sched/fair: Prevent dead task groups from regaining cfs_rq's
Kevin is reporting crashes which point to a use-after-free of a cfs_rq
in update_blocked_averages(). Initial debugging revealed that we've
live cfs_rq's (on_list=1) in an about to be kfree()'d task group in
free_fair_sched_group(). However, it was unclear how that can happen.
His kernel config happened to lead to a layout of struct sched_entity
that put the 'my_q' member directly into the middle of the object
which makes it incidentally overlap with SLUB's freelist pointer.
That, in combination with SLAB_FREELIST_HARDENED's freelist pointer
mangling, leads to a reliable access violation in form of a #GP which
made the UAF fail fast.
Michal seems to have run into the same issue[1]. He already correctly
diagnosed that commit a7b359fc6a37 ("sched/fair: Correctly insert
cfs_rq's to list on unthrottle") is causing the preconditions for the
UAF to happen by re-adding cfs_rq's also to task groups that have no
more running tasks, i.e. also to dead ones. His analysis, however,
misses the real root cause and it cannot be seen from the crash
backtrace only, as the real offender is tg_unthrottle_up() getting
called via sched_cfs_period_timer() via the timer interrupt at an
inconvenient time.
When unregister_fair_sched_group() unlinks all cfs_rq's from the dying
task group, it doesn't protect itself from getting interrupted. If the
timer interrupt triggers while we iterate over all CPUs or after
unregister_fair_sched_group() has finished but prior to unlinking the
task group, sched_cfs_period_timer() will execute and walk the list of
task groups, trying to unthrottle cfs_rq's, i.e. re-add them to the
dying task group. These will later -- in free_fair_sched_group() -- be
kfree()'ed while still being linked, leading to the fireworks Kevin
and Michal are seeing.
To fix this race, ensure the dying task group gets unlinked first.
However, simply switching the order of unregistering and unlinking the
task group isn't sufficient, as concurrent RCU walkers might still see
it, as can be seen below:
CPU1: CPU2:
: timer IRQ:
: do_sched_cfs_period_timer():
: :
: distribute_cfs_runtime():
: rcu_read_lock();
: :
: unthrottle_cfs_rq():
sched_offline_group(): :
: walk_tg_tree_from(…,tg_unthrottle_up,…):
list_del_rcu(&tg->list); :
(1) : list_for_each_entry_rcu(child, &parent->children, siblings)
: :
(2) list_del_rcu(&tg->siblings); :
: tg_unthrottle_up():
unregister_fair_sched_group(): struct cfs_rq *cfs_rq = tg->cfs_rq[cpu_of(rq)];
: :
list_del_leaf_cfs_rq(tg->cfs_rq[cpu]); :
: :
: if (!cfs_rq_is_decayed(cfs_rq) || cfs_rq->nr_running)
(3) : list_add_leaf_cfs_rq(cfs_rq);
: :
: :
: :
: :
: :
(4) : rcu_read_unlock();
CPU 2 walks the task group list in parallel to sched_offline_group(),
specifically, it'll read the soon to be unlinked task group entry at
(1). Unlinking it on CPU 1 at (2) therefore won't prevent CPU 2 from
still passing it on to tg_unthrottle_up(). CPU 1 now tries to unlink
all cfs_rq's via list_del_leaf_cfs_rq() in
unregister_fair_sched_group(). Meanwhile CPU 2 will re-add some of
these at (3), which is the cause of the UAF later on.
To prevent this additional race from happening, we need to wait until
walk_tg_tree_from() has finished traversing the task groups, i.e.
after the RCU read critical section ends in (4). Afterwards we're safe
to call unregister_fair_sched_group(), as each new walk won't see the
dying task group any more.
On top of that, we need to wait yet another RCU grace period after
unregister_fair_sched_group() to ensure print_cfs_stats(), which might
run concurrently, always sees valid objects, i.e. not already free'd
ones.
This patch survives Michal's reproducer[2] for 8h+ now, which used to
trigger within minutes before.
[1] https://lore.kernel.org/lkml/20211011172236.11223-1-mkoutny@suse.com/
[2] https://lore.kernel.org/lkml/20211102160228.GA57072@blackbody.suse.cz/
Fixes: a7b359fc6a37 ("sched/fair: Correctly insert cfs_rq's to list on unthrottle")
[peterz: shuffle code around a bit]
Reported-by: Kevin Tanguy <kevin.tanguy@corp.ovh.com>
Signed-off-by: Mathias Krause <minipli@grsecurity.net>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
2021-11-03 19:06:13 +00:00
|
|
|
}
|
|
|
|
|
|
|
|
void free_rt_sched_group(struct task_group *tg)
|
|
|
|
{
|
|
|
|
int i;
|
|
|
|
|
2011-10-25 08:00:11 +00:00
|
|
|
for_each_possible_cpu(i) {
|
|
|
|
if (tg->rt_rq)
|
|
|
|
kfree(tg->rt_rq[i]);
|
|
|
|
if (tg->rt_se)
|
|
|
|
kfree(tg->rt_se[i]);
|
|
|
|
}
|
|
|
|
|
|
|
|
kfree(tg->rt_rq);
|
|
|
|
kfree(tg->rt_se);
|
|
|
|
}
|
|
|
|
|
|
|
|
void init_tg_rt_entry(struct task_group *tg, struct rt_rq *rt_rq,
|
|
|
|
struct sched_rt_entity *rt_se, int cpu,
|
|
|
|
struct sched_rt_entity *parent)
|
|
|
|
{
|
|
|
|
struct rq *rq = cpu_rq(cpu);
|
|
|
|
|
2020-10-14 19:06:49 +00:00
|
|
|
rt_rq->highest_prio.curr = MAX_RT_PRIO-1;
|
2011-10-25 08:00:11 +00:00
|
|
|
rt_rq->rt_nr_boosted = 0;
|
|
|
|
rt_rq->rq = rq;
|
|
|
|
rt_rq->tg = tg;
|
|
|
|
|
|
|
|
tg->rt_rq[cpu] = rt_rq;
|
|
|
|
tg->rt_se[cpu] = rt_se;
|
|
|
|
|
|
|
|
if (!rt_se)
|
|
|
|
return;
|
|
|
|
|
|
|
|
if (!parent)
|
|
|
|
rt_se->rt_rq = &rq->rt;
|
|
|
|
else
|
|
|
|
rt_se->rt_rq = parent->my_q;
|
|
|
|
|
|
|
|
rt_se->my_q = rt_rq;
|
|
|
|
rt_se->parent = parent;
|
|
|
|
INIT_LIST_HEAD(&rt_se->run_list);
|
|
|
|
}
|
|
|
|
|
|
|
|
int alloc_rt_sched_group(struct task_group *tg, struct task_group *parent)
|
|
|
|
{
|
|
|
|
struct rt_rq *rt_rq;
|
|
|
|
struct sched_rt_entity *rt_se;
|
|
|
|
int i;
|
|
|
|
|
treewide: kzalloc() -> kcalloc()
The kzalloc() function has a 2-factor argument form, kcalloc(). This
patch replaces cases of:
kzalloc(a * b, gfp)
with:
kcalloc(a * b, gfp)
as well as handling cases of:
kzalloc(a * b * c, gfp)
with:
kzalloc(array3_size(a, b, c), gfp)
as it's slightly less ugly than:
kzalloc_array(array_size(a, b), c, gfp)
This does, however, attempt to ignore constant size factors like:
kzalloc(4 * 1024, gfp)
though any constants defined via macros get caught up in the conversion.
Any factors with a sizeof() of "unsigned char", "char", and "u8" were
dropped, since they're redundant.
The Coccinelle script used for this was:
// Fix redundant parens around sizeof().
@@
type TYPE;
expression THING, E;
@@
(
kzalloc(
- (sizeof(TYPE)) * E
+ sizeof(TYPE) * E
, ...)
|
kzalloc(
- (sizeof(THING)) * E
+ sizeof(THING) * E
, ...)
)
// Drop single-byte sizes and redundant parens.
@@
expression COUNT;
typedef u8;
typedef __u8;
@@
(
kzalloc(
- sizeof(u8) * (COUNT)
+ COUNT
, ...)
|
kzalloc(
- sizeof(__u8) * (COUNT)
+ COUNT
, ...)
|
kzalloc(
- sizeof(char) * (COUNT)
+ COUNT
, ...)
|
kzalloc(
- sizeof(unsigned char) * (COUNT)
+ COUNT
, ...)
|
kzalloc(
- sizeof(u8) * COUNT
+ COUNT
, ...)
|
kzalloc(
- sizeof(__u8) * COUNT
+ COUNT
, ...)
|
kzalloc(
- sizeof(char) * COUNT
+ COUNT
, ...)
|
kzalloc(
- sizeof(unsigned char) * COUNT
+ COUNT
, ...)
)
// 2-factor product with sizeof(type/expression) and identifier or constant.
@@
type TYPE;
expression THING;
identifier COUNT_ID;
constant COUNT_CONST;
@@
(
- kzalloc
+ kcalloc
(
- sizeof(TYPE) * (COUNT_ID)
+ COUNT_ID, sizeof(TYPE)
, ...)
|
- kzalloc
+ kcalloc
(
- sizeof(TYPE) * COUNT_ID
+ COUNT_ID, sizeof(TYPE)
, ...)
|
- kzalloc
+ kcalloc
(
- sizeof(TYPE) * (COUNT_CONST)
+ COUNT_CONST, sizeof(TYPE)
, ...)
|
- kzalloc
+ kcalloc
(
- sizeof(TYPE) * COUNT_CONST
+ COUNT_CONST, sizeof(TYPE)
, ...)
|
- kzalloc
+ kcalloc
(
- sizeof(THING) * (COUNT_ID)
+ COUNT_ID, sizeof(THING)
, ...)
|
- kzalloc
+ kcalloc
(
- sizeof(THING) * COUNT_ID
+ COUNT_ID, sizeof(THING)
, ...)
|
- kzalloc
+ kcalloc
(
- sizeof(THING) * (COUNT_CONST)
+ COUNT_CONST, sizeof(THING)
, ...)
|
- kzalloc
+ kcalloc
(
- sizeof(THING) * COUNT_CONST
+ COUNT_CONST, sizeof(THING)
, ...)
)
// 2-factor product, only identifiers.
@@
identifier SIZE, COUNT;
@@
- kzalloc
+ kcalloc
(
- SIZE * COUNT
+ COUNT, SIZE
, ...)
// 3-factor product with 1 sizeof(type) or sizeof(expression), with
// redundant parens removed.
@@
expression THING;
identifier STRIDE, COUNT;
type TYPE;
@@
(
kzalloc(
- sizeof(TYPE) * (COUNT) * (STRIDE)
+ array3_size(COUNT, STRIDE, sizeof(TYPE))
, ...)
|
kzalloc(
- sizeof(TYPE) * (COUNT) * STRIDE
+ array3_size(COUNT, STRIDE, sizeof(TYPE))
, ...)
|
kzalloc(
- sizeof(TYPE) * COUNT * (STRIDE)
+ array3_size(COUNT, STRIDE, sizeof(TYPE))
, ...)
|
kzalloc(
- sizeof(TYPE) * COUNT * STRIDE
+ array3_size(COUNT, STRIDE, sizeof(TYPE))
, ...)
|
kzalloc(
- sizeof(THING) * (COUNT) * (STRIDE)
+ array3_size(COUNT, STRIDE, sizeof(THING))
, ...)
|
kzalloc(
- sizeof(THING) * (COUNT) * STRIDE
+ array3_size(COUNT, STRIDE, sizeof(THING))
, ...)
|
kzalloc(
- sizeof(THING) * COUNT * (STRIDE)
+ array3_size(COUNT, STRIDE, sizeof(THING))
, ...)
|
kzalloc(
- sizeof(THING) * COUNT * STRIDE
+ array3_size(COUNT, STRIDE, sizeof(THING))
, ...)
)
// 3-factor product with 2 sizeof(variable), with redundant parens removed.
@@
expression THING1, THING2;
identifier COUNT;
type TYPE1, TYPE2;
@@
(
kzalloc(
- sizeof(TYPE1) * sizeof(TYPE2) * COUNT
+ array3_size(COUNT, sizeof(TYPE1), sizeof(TYPE2))
, ...)
|
kzalloc(
- sizeof(TYPE1) * sizeof(THING2) * (COUNT)
+ array3_size(COUNT, sizeof(TYPE1), sizeof(TYPE2))
, ...)
|
kzalloc(
- sizeof(THING1) * sizeof(THING2) * COUNT
+ array3_size(COUNT, sizeof(THING1), sizeof(THING2))
, ...)
|
kzalloc(
- sizeof(THING1) * sizeof(THING2) * (COUNT)
+ array3_size(COUNT, sizeof(THING1), sizeof(THING2))
, ...)
|
kzalloc(
- sizeof(TYPE1) * sizeof(THING2) * COUNT
+ array3_size(COUNT, sizeof(TYPE1), sizeof(THING2))
, ...)
|
kzalloc(
- sizeof(TYPE1) * sizeof(THING2) * (COUNT)
+ array3_size(COUNT, sizeof(TYPE1), sizeof(THING2))
, ...)
)
// 3-factor product, only identifiers, with redundant parens removed.
@@
identifier STRIDE, SIZE, COUNT;
@@
(
kzalloc(
- (COUNT) * STRIDE * SIZE
+ array3_size(COUNT, STRIDE, SIZE)
, ...)
|
kzalloc(
- COUNT * (STRIDE) * SIZE
+ array3_size(COUNT, STRIDE, SIZE)
, ...)
|
kzalloc(
- COUNT * STRIDE * (SIZE)
+ array3_size(COUNT, STRIDE, SIZE)
, ...)
|
kzalloc(
- (COUNT) * (STRIDE) * SIZE
+ array3_size(COUNT, STRIDE, SIZE)
, ...)
|
kzalloc(
- COUNT * (STRIDE) * (SIZE)
+ array3_size(COUNT, STRIDE, SIZE)
, ...)
|
kzalloc(
- (COUNT) * STRIDE * (SIZE)
+ array3_size(COUNT, STRIDE, SIZE)
, ...)
|
kzalloc(
- (COUNT) * (STRIDE) * (SIZE)
+ array3_size(COUNT, STRIDE, SIZE)
, ...)
|
kzalloc(
- COUNT * STRIDE * SIZE
+ array3_size(COUNT, STRIDE, SIZE)
, ...)
)
// Any remaining multi-factor products, first at least 3-factor products,
// when they're not all constants...
@@
expression E1, E2, E3;
constant C1, C2, C3;
@@
(
kzalloc(C1 * C2 * C3, ...)
|
kzalloc(
- (E1) * E2 * E3
+ array3_size(E1, E2, E3)
, ...)
|
kzalloc(
- (E1) * (E2) * E3
+ array3_size(E1, E2, E3)
, ...)
|
kzalloc(
- (E1) * (E2) * (E3)
+ array3_size(E1, E2, E3)
, ...)
|
kzalloc(
- E1 * E2 * E3
+ array3_size(E1, E2, E3)
, ...)
)
// And then all remaining 2 factors products when they're not all constants,
// keeping sizeof() as the second factor argument.
@@
expression THING, E1, E2;
type TYPE;
constant C1, C2, C3;
@@
(
kzalloc(sizeof(THING) * C2, ...)
|
kzalloc(sizeof(TYPE) * C2, ...)
|
kzalloc(C1 * C2 * C3, ...)
|
kzalloc(C1 * C2, ...)
|
- kzalloc
+ kcalloc
(
- sizeof(TYPE) * (E2)
+ E2, sizeof(TYPE)
, ...)
|
- kzalloc
+ kcalloc
(
- sizeof(TYPE) * E2
+ E2, sizeof(TYPE)
, ...)
|
- kzalloc
+ kcalloc
(
- sizeof(THING) * (E2)
+ E2, sizeof(THING)
, ...)
|
- kzalloc
+ kcalloc
(
- sizeof(THING) * E2
+ E2, sizeof(THING)
, ...)
|
- kzalloc
+ kcalloc
(
- (E1) * E2
+ E1, E2
, ...)
|
- kzalloc
+ kcalloc
(
- (E1) * (E2)
+ E1, E2
, ...)
|
- kzalloc
+ kcalloc
(
- E1 * E2
+ E1, E2
, ...)
)
Signed-off-by: Kees Cook <keescook@chromium.org>
2018-06-12 21:03:40 +00:00
|
|
|
tg->rt_rq = kcalloc(nr_cpu_ids, sizeof(rt_rq), GFP_KERNEL);
|
2011-10-25 08:00:11 +00:00
|
|
|
if (!tg->rt_rq)
|
|
|
|
goto err;
|
treewide: kzalloc() -> kcalloc()
The kzalloc() function has a 2-factor argument form, kcalloc(). This
patch replaces cases of:
kzalloc(a * b, gfp)
with:
kcalloc(a * b, gfp)
as well as handling cases of:
kzalloc(a * b * c, gfp)
with:
kzalloc(array3_size(a, b, c), gfp)
as it's slightly less ugly than:
kzalloc_array(array_size(a, b), c, gfp)
This does, however, attempt to ignore constant size factors like:
kzalloc(4 * 1024, gfp)
though any constants defined via macros get caught up in the conversion.
Any factors with a sizeof() of "unsigned char", "char", and "u8" were
dropped, since they're redundant.
The Coccinelle script used for this was:
// Fix redundant parens around sizeof().
@@
type TYPE;
expression THING, E;
@@
(
kzalloc(
- (sizeof(TYPE)) * E
+ sizeof(TYPE) * E
, ...)
|
kzalloc(
- (sizeof(THING)) * E
+ sizeof(THING) * E
, ...)
)
// Drop single-byte sizes and redundant parens.
@@
expression COUNT;
typedef u8;
typedef __u8;
@@
(
kzalloc(
- sizeof(u8) * (COUNT)
+ COUNT
, ...)
|
kzalloc(
- sizeof(__u8) * (COUNT)
+ COUNT
, ...)
|
kzalloc(
- sizeof(char) * (COUNT)
+ COUNT
, ...)
|
kzalloc(
- sizeof(unsigned char) * (COUNT)
+ COUNT
, ...)
|
kzalloc(
- sizeof(u8) * COUNT
+ COUNT
, ...)
|
kzalloc(
- sizeof(__u8) * COUNT
+ COUNT
, ...)
|
kzalloc(
- sizeof(char) * COUNT
+ COUNT
, ...)
|
kzalloc(
- sizeof(unsigned char) * COUNT
+ COUNT
, ...)
)
// 2-factor product with sizeof(type/expression) and identifier or constant.
@@
type TYPE;
expression THING;
identifier COUNT_ID;
constant COUNT_CONST;
@@
(
- kzalloc
+ kcalloc
(
- sizeof(TYPE) * (COUNT_ID)
+ COUNT_ID, sizeof(TYPE)
, ...)
|
- kzalloc
+ kcalloc
(
- sizeof(TYPE) * COUNT_ID
+ COUNT_ID, sizeof(TYPE)
, ...)
|
- kzalloc
+ kcalloc
(
- sizeof(TYPE) * (COUNT_CONST)
+ COUNT_CONST, sizeof(TYPE)
, ...)
|
- kzalloc
+ kcalloc
(
- sizeof(TYPE) * COUNT_CONST
+ COUNT_CONST, sizeof(TYPE)
, ...)
|
- kzalloc
+ kcalloc
(
- sizeof(THING) * (COUNT_ID)
+ COUNT_ID, sizeof(THING)
, ...)
|
- kzalloc
+ kcalloc
(
- sizeof(THING) * COUNT_ID
+ COUNT_ID, sizeof(THING)
, ...)
|
- kzalloc
+ kcalloc
(
- sizeof(THING) * (COUNT_CONST)
+ COUNT_CONST, sizeof(THING)
, ...)
|
- kzalloc
+ kcalloc
(
- sizeof(THING) * COUNT_CONST
+ COUNT_CONST, sizeof(THING)
, ...)
)
// 2-factor product, only identifiers.
@@
identifier SIZE, COUNT;
@@
- kzalloc
+ kcalloc
(
- SIZE * COUNT
+ COUNT, SIZE
, ...)
// 3-factor product with 1 sizeof(type) or sizeof(expression), with
// redundant parens removed.
@@
expression THING;
identifier STRIDE, COUNT;
type TYPE;
@@
(
kzalloc(
- sizeof(TYPE) * (COUNT) * (STRIDE)
+ array3_size(COUNT, STRIDE, sizeof(TYPE))
, ...)
|
kzalloc(
- sizeof(TYPE) * (COUNT) * STRIDE
+ array3_size(COUNT, STRIDE, sizeof(TYPE))
, ...)
|
kzalloc(
- sizeof(TYPE) * COUNT * (STRIDE)
+ array3_size(COUNT, STRIDE, sizeof(TYPE))
, ...)
|
kzalloc(
- sizeof(TYPE) * COUNT * STRIDE
+ array3_size(COUNT, STRIDE, sizeof(TYPE))
, ...)
|
kzalloc(
- sizeof(THING) * (COUNT) * (STRIDE)
+ array3_size(COUNT, STRIDE, sizeof(THING))
, ...)
|
kzalloc(
- sizeof(THING) * (COUNT) * STRIDE
+ array3_size(COUNT, STRIDE, sizeof(THING))
, ...)
|
kzalloc(
- sizeof(THING) * COUNT * (STRIDE)
+ array3_size(COUNT, STRIDE, sizeof(THING))
, ...)
|
kzalloc(
- sizeof(THING) * COUNT * STRIDE
+ array3_size(COUNT, STRIDE, sizeof(THING))
, ...)
)
// 3-factor product with 2 sizeof(variable), with redundant parens removed.
@@
expression THING1, THING2;
identifier COUNT;
type TYPE1, TYPE2;
@@
(
kzalloc(
- sizeof(TYPE1) * sizeof(TYPE2) * COUNT
+ array3_size(COUNT, sizeof(TYPE1), sizeof(TYPE2))
, ...)
|
kzalloc(
- sizeof(TYPE1) * sizeof(THING2) * (COUNT)
+ array3_size(COUNT, sizeof(TYPE1), sizeof(TYPE2))
, ...)
|
kzalloc(
- sizeof(THING1) * sizeof(THING2) * COUNT
+ array3_size(COUNT, sizeof(THING1), sizeof(THING2))
, ...)
|
kzalloc(
- sizeof(THING1) * sizeof(THING2) * (COUNT)
+ array3_size(COUNT, sizeof(THING1), sizeof(THING2))
, ...)
|
kzalloc(
- sizeof(TYPE1) * sizeof(THING2) * COUNT
+ array3_size(COUNT, sizeof(TYPE1), sizeof(THING2))
, ...)
|
kzalloc(
- sizeof(TYPE1) * sizeof(THING2) * (COUNT)
+ array3_size(COUNT, sizeof(TYPE1), sizeof(THING2))
, ...)
)
// 3-factor product, only identifiers, with redundant parens removed.
@@
identifier STRIDE, SIZE, COUNT;
@@
(
kzalloc(
- (COUNT) * STRIDE * SIZE
+ array3_size(COUNT, STRIDE, SIZE)
, ...)
|
kzalloc(
- COUNT * (STRIDE) * SIZE
+ array3_size(COUNT, STRIDE, SIZE)
, ...)
|
kzalloc(
- COUNT * STRIDE * (SIZE)
+ array3_size(COUNT, STRIDE, SIZE)
, ...)
|
kzalloc(
- (COUNT) * (STRIDE) * SIZE
+ array3_size(COUNT, STRIDE, SIZE)
, ...)
|
kzalloc(
- COUNT * (STRIDE) * (SIZE)
+ array3_size(COUNT, STRIDE, SIZE)
, ...)
|
kzalloc(
- (COUNT) * STRIDE * (SIZE)
+ array3_size(COUNT, STRIDE, SIZE)
, ...)
|
kzalloc(
- (COUNT) * (STRIDE) * (SIZE)
+ array3_size(COUNT, STRIDE, SIZE)
, ...)
|
kzalloc(
- COUNT * STRIDE * SIZE
+ array3_size(COUNT, STRIDE, SIZE)
, ...)
)
// Any remaining multi-factor products, first at least 3-factor products,
// when they're not all constants...
@@
expression E1, E2, E3;
constant C1, C2, C3;
@@
(
kzalloc(C1 * C2 * C3, ...)
|
kzalloc(
- (E1) * E2 * E3
+ array3_size(E1, E2, E3)
, ...)
|
kzalloc(
- (E1) * (E2) * E3
+ array3_size(E1, E2, E3)
, ...)
|
kzalloc(
- (E1) * (E2) * (E3)
+ array3_size(E1, E2, E3)
, ...)
|
kzalloc(
- E1 * E2 * E3
+ array3_size(E1, E2, E3)
, ...)
)
// And then all remaining 2 factors products when they're not all constants,
// keeping sizeof() as the second factor argument.
@@
expression THING, E1, E2;
type TYPE;
constant C1, C2, C3;
@@
(
kzalloc(sizeof(THING) * C2, ...)
|
kzalloc(sizeof(TYPE) * C2, ...)
|
kzalloc(C1 * C2 * C3, ...)
|
kzalloc(C1 * C2, ...)
|
- kzalloc
+ kcalloc
(
- sizeof(TYPE) * (E2)
+ E2, sizeof(TYPE)
, ...)
|
- kzalloc
+ kcalloc
(
- sizeof(TYPE) * E2
+ E2, sizeof(TYPE)
, ...)
|
- kzalloc
+ kcalloc
(
- sizeof(THING) * (E2)
+ E2, sizeof(THING)
, ...)
|
- kzalloc
+ kcalloc
(
- sizeof(THING) * E2
+ E2, sizeof(THING)
, ...)
|
- kzalloc
+ kcalloc
(
- (E1) * E2
+ E1, E2
, ...)
|
- kzalloc
+ kcalloc
(
- (E1) * (E2)
+ E1, E2
, ...)
|
- kzalloc
+ kcalloc
(
- E1 * E2
+ E1, E2
, ...)
)
Signed-off-by: Kees Cook <keescook@chromium.org>
2018-06-12 21:03:40 +00:00
|
|
|
tg->rt_se = kcalloc(nr_cpu_ids, sizeof(rt_se), GFP_KERNEL);
|
2011-10-25 08:00:11 +00:00
|
|
|
if (!tg->rt_se)
|
|
|
|
goto err;
|
|
|
|
|
|
|
|
init_rt_bandwidth(&tg->rt_bandwidth,
|
|
|
|
ktime_to_ns(def_rt_bandwidth.rt_period), 0);
|
|
|
|
|
|
|
|
for_each_possible_cpu(i) {
|
|
|
|
rt_rq = kzalloc_node(sizeof(struct rt_rq),
|
|
|
|
GFP_KERNEL, cpu_to_node(i));
|
|
|
|
if (!rt_rq)
|
|
|
|
goto err;
|
|
|
|
|
|
|
|
rt_se = kzalloc_node(sizeof(struct sched_rt_entity),
|
|
|
|
GFP_KERNEL, cpu_to_node(i));
|
|
|
|
if (!rt_se)
|
|
|
|
goto err_free_rq;
|
|
|
|
|
2015-03-03 11:50:27 +00:00
|
|
|
init_rt_rq(rt_rq);
|
2011-10-25 08:00:11 +00:00
|
|
|
rt_rq->rt_runtime = tg->rt_bandwidth.rt_runtime;
|
|
|
|
init_tg_rt_entry(tg, rt_rq, rt_se, i, parent->rt_se[i]);
|
|
|
|
}
|
|
|
|
|
|
|
|
return 1;
|
|
|
|
|
|
|
|
err_free_rq:
|
|
|
|
kfree(rt_rq);
|
|
|
|
err:
|
|
|
|
return 0;
|
|
|
|
}
|
|
|
|
|
2009-01-14 14:10:04 +00:00
|
|
|
#else /* CONFIG_RT_GROUP_SCHED */
|
|
|
|
|
2009-04-01 16:40:15 +00:00
|
|
|
#define rt_entity_is_task(rt_se) (1)
|
|
|
|
|
2009-07-24 10:25:30 +00:00
|
|
|
static inline struct task_struct *rt_task_of(struct sched_rt_entity *rt_se)
|
|
|
|
{
|
|
|
|
return container_of(rt_se, struct task_struct, rt);
|
|
|
|
}
|
|
|
|
|
2009-01-14 14:10:04 +00:00
|
|
|
static inline struct rq *rq_of_rt_rq(struct rt_rq *rt_rq)
|
|
|
|
{
|
|
|
|
return container_of(rt_rq, struct rq, rt);
|
|
|
|
}
|
|
|
|
|
2014-03-14 22:14:55 +00:00
|
|
|
static inline struct rq *rq_of_rt_se(struct sched_rt_entity *rt_se)
|
2009-01-14 14:10:04 +00:00
|
|
|
{
|
|
|
|
struct task_struct *p = rt_task_of(rt_se);
|
2014-03-14 22:14:55 +00:00
|
|
|
|
|
|
|
return task_rq(p);
|
|
|
|
}
|
|
|
|
|
|
|
|
static inline struct rt_rq *rt_rq_of_se(struct sched_rt_entity *rt_se)
|
|
|
|
{
|
|
|
|
struct rq *rq = rq_of_rt_se(rt_se);
|
2009-01-14 14:10:04 +00:00
|
|
|
|
|
|
|
return &rq->rt;
|
|
|
|
}
|
|
|
|
|
sched/fair: Prevent dead task groups from regaining cfs_rq's
Kevin is reporting crashes which point to a use-after-free of a cfs_rq
in update_blocked_averages(). Initial debugging revealed that we've
live cfs_rq's (on_list=1) in an about to be kfree()'d task group in
free_fair_sched_group(). However, it was unclear how that can happen.
His kernel config happened to lead to a layout of struct sched_entity
that put the 'my_q' member directly into the middle of the object
which makes it incidentally overlap with SLUB's freelist pointer.
That, in combination with SLAB_FREELIST_HARDENED's freelist pointer
mangling, leads to a reliable access violation in form of a #GP which
made the UAF fail fast.
Michal seems to have run into the same issue[1]. He already correctly
diagnosed that commit a7b359fc6a37 ("sched/fair: Correctly insert
cfs_rq's to list on unthrottle") is causing the preconditions for the
UAF to happen by re-adding cfs_rq's also to task groups that have no
more running tasks, i.e. also to dead ones. His analysis, however,
misses the real root cause and it cannot be seen from the crash
backtrace only, as the real offender is tg_unthrottle_up() getting
called via sched_cfs_period_timer() via the timer interrupt at an
inconvenient time.
When unregister_fair_sched_group() unlinks all cfs_rq's from the dying
task group, it doesn't protect itself from getting interrupted. If the
timer interrupt triggers while we iterate over all CPUs or after
unregister_fair_sched_group() has finished but prior to unlinking the
task group, sched_cfs_period_timer() will execute and walk the list of
task groups, trying to unthrottle cfs_rq's, i.e. re-add them to the
dying task group. These will later -- in free_fair_sched_group() -- be
kfree()'ed while still being linked, leading to the fireworks Kevin
and Michal are seeing.
To fix this race, ensure the dying task group gets unlinked first.
However, simply switching the order of unregistering and unlinking the
task group isn't sufficient, as concurrent RCU walkers might still see
it, as can be seen below:
CPU1: CPU2:
: timer IRQ:
: do_sched_cfs_period_timer():
: :
: distribute_cfs_runtime():
: rcu_read_lock();
: :
: unthrottle_cfs_rq():
sched_offline_group(): :
: walk_tg_tree_from(…,tg_unthrottle_up,…):
list_del_rcu(&tg->list); :
(1) : list_for_each_entry_rcu(child, &parent->children, siblings)
: :
(2) list_del_rcu(&tg->siblings); :
: tg_unthrottle_up():
unregister_fair_sched_group(): struct cfs_rq *cfs_rq = tg->cfs_rq[cpu_of(rq)];
: :
list_del_leaf_cfs_rq(tg->cfs_rq[cpu]); :
: :
: if (!cfs_rq_is_decayed(cfs_rq) || cfs_rq->nr_running)
(3) : list_add_leaf_cfs_rq(cfs_rq);
: :
: :
: :
: :
: :
(4) : rcu_read_unlock();
CPU 2 walks the task group list in parallel to sched_offline_group(),
specifically, it'll read the soon to be unlinked task group entry at
(1). Unlinking it on CPU 1 at (2) therefore won't prevent CPU 2 from
still passing it on to tg_unthrottle_up(). CPU 1 now tries to unlink
all cfs_rq's via list_del_leaf_cfs_rq() in
unregister_fair_sched_group(). Meanwhile CPU 2 will re-add some of
these at (3), which is the cause of the UAF later on.
To prevent this additional race from happening, we need to wait until
walk_tg_tree_from() has finished traversing the task groups, i.e.
after the RCU read critical section ends in (4). Afterwards we're safe
to call unregister_fair_sched_group(), as each new walk won't see the
dying task group any more.
On top of that, we need to wait yet another RCU grace period after
unregister_fair_sched_group() to ensure print_cfs_stats(), which might
run concurrently, always sees valid objects, i.e. not already free'd
ones.
This patch survives Michal's reproducer[2] for 8h+ now, which used to
trigger within minutes before.
[1] https://lore.kernel.org/lkml/20211011172236.11223-1-mkoutny@suse.com/
[2] https://lore.kernel.org/lkml/20211102160228.GA57072@blackbody.suse.cz/
Fixes: a7b359fc6a37 ("sched/fair: Correctly insert cfs_rq's to list on unthrottle")
[peterz: shuffle code around a bit]
Reported-by: Kevin Tanguy <kevin.tanguy@corp.ovh.com>
Signed-off-by: Mathias Krause <minipli@grsecurity.net>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
2021-11-03 19:06:13 +00:00
|
|
|
void unregister_rt_sched_group(struct task_group *tg) { }
|
|
|
|
|
2011-10-25 08:00:11 +00:00
|
|
|
void free_rt_sched_group(struct task_group *tg) { }
|
|
|
|
|
|
|
|
int alloc_rt_sched_group(struct task_group *tg, struct task_group *parent)
|
|
|
|
{
|
|
|
|
return 1;
|
|
|
|
}
|
2009-01-14 14:10:04 +00:00
|
|
|
#endif /* CONFIG_RT_GROUP_SCHED */
|
|
|
|
|
2008-01-25 20:08:06 +00:00
|
|
|
#ifdef CONFIG_SMP
|
2008-01-25 20:08:15 +00:00
|
|
|
|
2014-02-12 14:47:29 +00:00
|
|
|
static inline bool need_pull_rt_task(struct rq *rq, struct task_struct *prev)
|
|
|
|
{
|
|
|
|
/* Try to pull RT tasks here if we lower this rq's prio */
|
2020-09-25 14:42:31 +00:00
|
|
|
return rq->online && rq->rt.highest_prio.curr > prev->prio;
|
2014-02-12 14:47:29 +00:00
|
|
|
}
|
|
|
|
|
2008-01-25 20:08:18 +00:00
|
|
|
static inline int rt_overloaded(struct rq *rq)
|
2008-01-25 20:08:06 +00:00
|
|
|
{
|
2008-01-25 20:08:18 +00:00
|
|
|
return atomic_read(&rq->rd->rto_count);
|
2008-01-25 20:08:06 +00:00
|
|
|
}
|
2008-01-25 20:08:15 +00:00
|
|
|
|
2008-01-25 20:08:06 +00:00
|
|
|
static inline void rt_set_overload(struct rq *rq)
|
|
|
|
{
|
2008-06-04 19:04:05 +00:00
|
|
|
if (!rq->online)
|
|
|
|
return;
|
|
|
|
|
2008-11-24 16:05:05 +00:00
|
|
|
cpumask_set_cpu(rq->cpu, rq->rd->rto_mask);
|
2008-01-25 20:08:06 +00:00
|
|
|
/*
|
|
|
|
* Make sure the mask is visible before we set
|
|
|
|
* the overload count. That is checked to determine
|
|
|
|
* if we should look at the mask. It would be a shame
|
|
|
|
* if we looked at the mask, but the mask was not
|
|
|
|
* updated yet.
|
2013-10-15 10:35:07 +00:00
|
|
|
*
|
|
|
|
* Matched by the barrier in pull_rt_task().
|
2008-01-25 20:08:06 +00:00
|
|
|
*/
|
2013-10-15 10:35:07 +00:00
|
|
|
smp_wmb();
|
2008-01-25 20:08:18 +00:00
|
|
|
atomic_inc(&rq->rd->rto_count);
|
2008-01-25 20:08:06 +00:00
|
|
|
}
|
2008-01-25 20:08:15 +00:00
|
|
|
|
2008-01-25 20:08:06 +00:00
|
|
|
static inline void rt_clear_overload(struct rq *rq)
|
|
|
|
{
|
2008-06-04 19:04:05 +00:00
|
|
|
if (!rq->online)
|
|
|
|
return;
|
|
|
|
|
2008-01-25 20:08:06 +00:00
|
|
|
/* the order here really doesn't matter */
|
2008-01-25 20:08:18 +00:00
|
|
|
atomic_dec(&rq->rd->rto_count);
|
2008-11-24 16:05:05 +00:00
|
|
|
cpumask_clear_cpu(rq->cpu, rq->rd->rto_mask);
|
2008-01-25 20:08:06 +00:00
|
|
|
}
|
2008-01-25 20:08:07 +00:00
|
|
|
|
2009-01-14 14:10:04 +00:00
|
|
|
static void update_rt_migration(struct rt_rq *rt_rq)
|
2008-01-25 20:08:07 +00:00
|
|
|
{
|
2009-04-01 16:40:15 +00:00
|
|
|
if (rt_rq->rt_nr_migratory && rt_rq->rt_nr_total > 1) {
|
2009-01-14 14:10:04 +00:00
|
|
|
if (!rt_rq->overloaded) {
|
|
|
|
rt_set_overload(rq_of_rt_rq(rt_rq));
|
|
|
|
rt_rq->overloaded = 1;
|
2008-01-25 20:08:23 +00:00
|
|
|
}
|
2009-01-14 14:10:04 +00:00
|
|
|
} else if (rt_rq->overloaded) {
|
|
|
|
rt_clear_overload(rq_of_rt_rq(rt_rq));
|
|
|
|
rt_rq->overloaded = 0;
|
2008-01-25 20:08:18 +00:00
|
|
|
}
|
2008-01-25 20:08:07 +00:00
|
|
|
}
|
2008-01-25 20:08:06 +00:00
|
|
|
|
2009-01-14 14:10:04 +00:00
|
|
|
static void inc_rt_migration(struct sched_rt_entity *rt_se, struct rt_rq *rt_rq)
|
|
|
|
{
|
2012-04-23 10:11:21 +00:00
|
|
|
struct task_struct *p;
|
|
|
|
|
2009-04-01 16:40:15 +00:00
|
|
|
if (!rt_entity_is_task(rt_se))
|
|
|
|
return;
|
|
|
|
|
2012-04-23 10:11:21 +00:00
|
|
|
p = rt_task_of(rt_se);
|
2009-04-01 16:40:15 +00:00
|
|
|
rt_rq = &rq_of_rt_rq(rt_rq)->rt;
|
|
|
|
|
|
|
|
rt_rq->rt_nr_total++;
|
2017-02-05 14:41:03 +00:00
|
|
|
if (p->nr_cpus_allowed > 1)
|
2009-01-14 14:10:04 +00:00
|
|
|
rt_rq->rt_nr_migratory++;
|
|
|
|
|
|
|
|
update_rt_migration(rt_rq);
|
|
|
|
}
|
|
|
|
|
|
|
|
static void dec_rt_migration(struct sched_rt_entity *rt_se, struct rt_rq *rt_rq)
|
|
|
|
{
|
2012-04-23 10:11:21 +00:00
|
|
|
struct task_struct *p;
|
|
|
|
|
2009-04-01 16:40:15 +00:00
|
|
|
if (!rt_entity_is_task(rt_se))
|
|
|
|
return;
|
|
|
|
|
2012-04-23 10:11:21 +00:00
|
|
|
p = rt_task_of(rt_se);
|
2009-04-01 16:40:15 +00:00
|
|
|
rt_rq = &rq_of_rt_rq(rt_rq)->rt;
|
|
|
|
|
|
|
|
rt_rq->rt_nr_total--;
|
2017-02-05 14:41:03 +00:00
|
|
|
if (p->nr_cpus_allowed > 1)
|
2009-01-14 14:10:04 +00:00
|
|
|
rt_rq->rt_nr_migratory--;
|
|
|
|
|
|
|
|
update_rt_migration(rt_rq);
|
|
|
|
}
|
|
|
|
|
sched: Use pushable_tasks to determine next highest prio
Hillf Danton proposed a patch (see link) that cleaned up the
sched_rt code that calculates the priority of the next highest priority
task to be used in finding run queues to pull from.
His patch removed the calculating of the next prio to just use the current
prio when deteriming if we should examine a run queue to pull from. The problem
with his patch was that it caused more false checks. Because we check a run
queue for pushable tasks if the current priority of that run queue is higher
in priority than the task about to run on our run queue. But after grabbing
the locks and doing the real check, we find that there may not be a task
that has a higher prio task to pull. Thus the locks were taken with nothing to
do.
I added some trace_printks() to record when and how many times the run queue
locks were taken to check for pullable tasks, compared to how many times we
pulled a task.
With the current method, it was:
3806 locks taken vs 2812 pulled tasks
With Hillf's patch:
6728 locks taken vs 2804 pulled tasks
The number of times locks were taken to pull a task went up almost double with
no more success rate.
But his patch did get me thinking. When we look at the priority of the highest
task to consider taking the locks to do a pull, a failure to pull can be one
of the following: (in order of most likely)
o RT task was pushed off already between the check and taking the lock
o Waiting RT task can not be migrated
o RT task's CPU affinity does not include the target run queue's CPU
o RT task's priority changed between the check and taking the lock
And with Hillf's patch, the thing that caused most of the failures, is
the RT task to pull was not at the right priority to pull (not greater than
the current RT task priority on the target run queue).
Most of the above cases we can't help. But the current method does not check
if the next highest prio RT task can be migrated or not, and if it can not,
we still grab the locks to do the test (we don't find out about this fact until
after we have the locks). I thought about this case, and realized that the
pushable task plist that is maintained only holds RT tasks that can migrate.
If we move the calculating of the next highest prio task from the inc/dec_rt_task()
functions into the queuing of the pushable tasks, then we only measure the
priorities of those tasks that we push, and we get this basically for free.
Not only does this patch make the code a little more efficient, it cleans it
up and makes it a little simpler.
Thanks to Hillf Danton for inspiring me on this patch.
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Hillf Danton <dhillf@gmail.com>
Cc: Gregory Haskins <ghaskins@novell.com>
Link: http://lkml.kernel.org/r/BANLkTimQ67180HxCx5vgMqumqw1EkFh3qg@mail.gmail.com
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2011-06-17 01:55:23 +00:00
|
|
|
static inline int has_pushable_tasks(struct rq *rq)
|
|
|
|
{
|
|
|
|
return !plist_head_empty(&rq->rt.pushable_tasks);
|
|
|
|
}
|
|
|
|
|
2022-10-08 00:07:58 +00:00
|
|
|
static DEFINE_PER_CPU(struct balance_callback, rt_push_head);
|
|
|
|
static DEFINE_PER_CPU(struct balance_callback, rt_pull_head);
|
2015-06-11 12:46:37 +00:00
|
|
|
|
|
|
|
static void push_rt_tasks(struct rq *);
|
2015-06-11 12:46:41 +00:00
|
|
|
static void pull_rt_task(struct rq *);
|
2015-06-11 12:46:37 +00:00
|
|
|
|
2018-03-03 15:27:54 +00:00
|
|
|
static inline void rt_queue_push_tasks(struct rq *rq)
|
2014-02-12 14:47:29 +00:00
|
|
|
{
|
2015-06-11 12:46:37 +00:00
|
|
|
if (!has_pushable_tasks(rq))
|
|
|
|
return;
|
|
|
|
|
2015-06-11 12:46:41 +00:00
|
|
|
queue_balance_callback(rq, &per_cpu(rt_push_head, rq->cpu), push_rt_tasks);
|
|
|
|
}
|
|
|
|
|
2018-03-03 15:27:54 +00:00
|
|
|
static inline void rt_queue_pull_task(struct rq *rq)
|
2015-06-11 12:46:41 +00:00
|
|
|
{
|
|
|
|
queue_balance_callback(rq, &per_cpu(rt_pull_head, rq->cpu), pull_rt_task);
|
2014-02-12 14:47:29 +00:00
|
|
|
}
|
|
|
|
|
sched: create "pushable_tasks" list to limit pushing to one attempt
The RT scheduler employs a "push/pull" design to actively balance tasks
within the system (on a per disjoint cpuset basis). When a task is
awoken, it is immediately determined if there are any lower priority
cpus which should be preempted. This is opposed to the way normal
SCHED_OTHER tasks behave, which will wait for a periodic rebalancing
operation to occur before spreading out load.
When a particular RQ has more than 1 active RT task, it is said to
be in an "overloaded" state. Once this occurs, the system enters
the active balancing mode, where it will try to push the task away,
or persuade a different cpu to pull it over. The system will stay
in this state until the system falls back below the <= 1 queued RT
task per RQ.
However, the current implementation suffers from a limitation in the
push logic. Once overloaded, all tasks (other than current) on the
RQ are analyzed on every push operation, even if it was previously
unpushable (due to affinity, etc). Whats more, the operation stops
at the first task that is unpushable and will not look at items
lower in the queue. This causes two problems:
1) We can have the same tasks analyzed over and over again during each
push, which extends out the fast path in the scheduler for no
gain. Consider a RQ that has dozens of tasks that are bound to a
core. Each one of those tasks will be encountered and skipped
for each push operation while they are queued.
2) There may be lower-priority tasks under the unpushable task that
could have been successfully pushed, but will never be considered
until either the unpushable task is cleared, or a pull operation
succeeds. The net result is a potential latency source for mid
priority tasks.
This patch aims to rectify these two conditions by introducing a new
priority sorted list: "pushable_tasks". A task is added to the list
each time a task is activated or preempted. It is removed from the
list any time it is deactivated, made current, or fails to push.
This works because a task only needs to be attempted to push once.
After an initial failure to push, the other cpus will eventually try to
pull the task when the conditions are proper. This also solves the
problem that we don't completely analyze all tasks due to encountering
an unpushable tasks. Now every task will have a push attempted (when
appropriate).
This reduces latency both by shorting the critical section of the
rq->lock for certain workloads, and by making sure the algorithm
considers all eligible tasks in the system.
[ rostedt: added a couple more BUG_ONs ]
Signed-off-by: Gregory Haskins <ghaskins@novell.com>
Acked-by: Steven Rostedt <srostedt@redhat.com>
2008-12-29 14:39:53 +00:00
|
|
|
static void enqueue_pushable_task(struct rq *rq, struct task_struct *p)
|
|
|
|
{
|
|
|
|
plist_del(&p->pushable_tasks, &rq->rt.pushable_tasks);
|
|
|
|
plist_node_init(&p->pushable_tasks, p->prio);
|
|
|
|
plist_add(&p->pushable_tasks, &rq->rt.pushable_tasks);
|
sched: Use pushable_tasks to determine next highest prio
Hillf Danton proposed a patch (see link) that cleaned up the
sched_rt code that calculates the priority of the next highest priority
task to be used in finding run queues to pull from.
His patch removed the calculating of the next prio to just use the current
prio when deteriming if we should examine a run queue to pull from. The problem
with his patch was that it caused more false checks. Because we check a run
queue for pushable tasks if the current priority of that run queue is higher
in priority than the task about to run on our run queue. But after grabbing
the locks and doing the real check, we find that there may not be a task
that has a higher prio task to pull. Thus the locks were taken with nothing to
do.
I added some trace_printks() to record when and how many times the run queue
locks were taken to check for pullable tasks, compared to how many times we
pulled a task.
With the current method, it was:
3806 locks taken vs 2812 pulled tasks
With Hillf's patch:
6728 locks taken vs 2804 pulled tasks
The number of times locks were taken to pull a task went up almost double with
no more success rate.
But his patch did get me thinking. When we look at the priority of the highest
task to consider taking the locks to do a pull, a failure to pull can be one
of the following: (in order of most likely)
o RT task was pushed off already between the check and taking the lock
o Waiting RT task can not be migrated
o RT task's CPU affinity does not include the target run queue's CPU
o RT task's priority changed between the check and taking the lock
And with Hillf's patch, the thing that caused most of the failures, is
the RT task to pull was not at the right priority to pull (not greater than
the current RT task priority on the target run queue).
Most of the above cases we can't help. But the current method does not check
if the next highest prio RT task can be migrated or not, and if it can not,
we still grab the locks to do the test (we don't find out about this fact until
after we have the locks). I thought about this case, and realized that the
pushable task plist that is maintained only holds RT tasks that can migrate.
If we move the calculating of the next highest prio task from the inc/dec_rt_task()
functions into the queuing of the pushable tasks, then we only measure the
priorities of those tasks that we push, and we get this basically for free.
Not only does this patch make the code a little more efficient, it cleans it
up and makes it a little simpler.
Thanks to Hillf Danton for inspiring me on this patch.
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Hillf Danton <dhillf@gmail.com>
Cc: Gregory Haskins <ghaskins@novell.com>
Link: http://lkml.kernel.org/r/BANLkTimQ67180HxCx5vgMqumqw1EkFh3qg@mail.gmail.com
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2011-06-17 01:55:23 +00:00
|
|
|
|
|
|
|
/* Update the highest prio pushable task */
|
|
|
|
if (p->prio < rq->rt.highest_prio.next)
|
|
|
|
rq->rt.highest_prio.next = p->prio;
|
sched: create "pushable_tasks" list to limit pushing to one attempt
The RT scheduler employs a "push/pull" design to actively balance tasks
within the system (on a per disjoint cpuset basis). When a task is
awoken, it is immediately determined if there are any lower priority
cpus which should be preempted. This is opposed to the way normal
SCHED_OTHER tasks behave, which will wait for a periodic rebalancing
operation to occur before spreading out load.
When a particular RQ has more than 1 active RT task, it is said to
be in an "overloaded" state. Once this occurs, the system enters
the active balancing mode, where it will try to push the task away,
or persuade a different cpu to pull it over. The system will stay
in this state until the system falls back below the <= 1 queued RT
task per RQ.
However, the current implementation suffers from a limitation in the
push logic. Once overloaded, all tasks (other than current) on the
RQ are analyzed on every push operation, even if it was previously
unpushable (due to affinity, etc). Whats more, the operation stops
at the first task that is unpushable and will not look at items
lower in the queue. This causes two problems:
1) We can have the same tasks analyzed over and over again during each
push, which extends out the fast path in the scheduler for no
gain. Consider a RQ that has dozens of tasks that are bound to a
core. Each one of those tasks will be encountered and skipped
for each push operation while they are queued.
2) There may be lower-priority tasks under the unpushable task that
could have been successfully pushed, but will never be considered
until either the unpushable task is cleared, or a pull operation
succeeds. The net result is a potential latency source for mid
priority tasks.
This patch aims to rectify these two conditions by introducing a new
priority sorted list: "pushable_tasks". A task is added to the list
each time a task is activated or preempted. It is removed from the
list any time it is deactivated, made current, or fails to push.
This works because a task only needs to be attempted to push once.
After an initial failure to push, the other cpus will eventually try to
pull the task when the conditions are proper. This also solves the
problem that we don't completely analyze all tasks due to encountering
an unpushable tasks. Now every task will have a push attempted (when
appropriate).
This reduces latency both by shorting the critical section of the
rq->lock for certain workloads, and by making sure the algorithm
considers all eligible tasks in the system.
[ rostedt: added a couple more BUG_ONs ]
Signed-off-by: Gregory Haskins <ghaskins@novell.com>
Acked-by: Steven Rostedt <srostedt@redhat.com>
2008-12-29 14:39:53 +00:00
|
|
|
}
|
|
|
|
|
|
|
|
static void dequeue_pushable_task(struct rq *rq, struct task_struct *p)
|
|
|
|
{
|
|
|
|
plist_del(&p->pushable_tasks, &rq->rt.pushable_tasks);
|
|
|
|
|
sched: Use pushable_tasks to determine next highest prio
Hillf Danton proposed a patch (see link) that cleaned up the
sched_rt code that calculates the priority of the next highest priority
task to be used in finding run queues to pull from.
His patch removed the calculating of the next prio to just use the current
prio when deteriming if we should examine a run queue to pull from. The problem
with his patch was that it caused more false checks. Because we check a run
queue for pushable tasks if the current priority of that run queue is higher
in priority than the task about to run on our run queue. But after grabbing
the locks and doing the real check, we find that there may not be a task
that has a higher prio task to pull. Thus the locks were taken with nothing to
do.
I added some trace_printks() to record when and how many times the run queue
locks were taken to check for pullable tasks, compared to how many times we
pulled a task.
With the current method, it was:
3806 locks taken vs 2812 pulled tasks
With Hillf's patch:
6728 locks taken vs 2804 pulled tasks
The number of times locks were taken to pull a task went up almost double with
no more success rate.
But his patch did get me thinking. When we look at the priority of the highest
task to consider taking the locks to do a pull, a failure to pull can be one
of the following: (in order of most likely)
o RT task was pushed off already between the check and taking the lock
o Waiting RT task can not be migrated
o RT task's CPU affinity does not include the target run queue's CPU
o RT task's priority changed between the check and taking the lock
And with Hillf's patch, the thing that caused most of the failures, is
the RT task to pull was not at the right priority to pull (not greater than
the current RT task priority on the target run queue).
Most of the above cases we can't help. But the current method does not check
if the next highest prio RT task can be migrated or not, and if it can not,
we still grab the locks to do the test (we don't find out about this fact until
after we have the locks). I thought about this case, and realized that the
pushable task plist that is maintained only holds RT tasks that can migrate.
If we move the calculating of the next highest prio task from the inc/dec_rt_task()
functions into the queuing of the pushable tasks, then we only measure the
priorities of those tasks that we push, and we get this basically for free.
Not only does this patch make the code a little more efficient, it cleans it
up and makes it a little simpler.
Thanks to Hillf Danton for inspiring me on this patch.
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Hillf Danton <dhillf@gmail.com>
Cc: Gregory Haskins <ghaskins@novell.com>
Link: http://lkml.kernel.org/r/BANLkTimQ67180HxCx5vgMqumqw1EkFh3qg@mail.gmail.com
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2011-06-17 01:55:23 +00:00
|
|
|
/* Update the new highest prio pushable task */
|
|
|
|
if (has_pushable_tasks(rq)) {
|
|
|
|
p = plist_first_entry(&rq->rt.pushable_tasks,
|
|
|
|
struct task_struct, pushable_tasks);
|
|
|
|
rq->rt.highest_prio.next = p->prio;
|
2020-10-14 19:06:49 +00:00
|
|
|
} else {
|
|
|
|
rq->rt.highest_prio.next = MAX_RT_PRIO-1;
|
|
|
|
}
|
2008-04-19 10:11:10 +00:00
|
|
|
}
|
|
|
|
|
sched: create "pushable_tasks" list to limit pushing to one attempt
The RT scheduler employs a "push/pull" design to actively balance tasks
within the system (on a per disjoint cpuset basis). When a task is
awoken, it is immediately determined if there are any lower priority
cpus which should be preempted. This is opposed to the way normal
SCHED_OTHER tasks behave, which will wait for a periodic rebalancing
operation to occur before spreading out load.
When a particular RQ has more than 1 active RT task, it is said to
be in an "overloaded" state. Once this occurs, the system enters
the active balancing mode, where it will try to push the task away,
or persuade a different cpu to pull it over. The system will stay
in this state until the system falls back below the <= 1 queued RT
task per RQ.
However, the current implementation suffers from a limitation in the
push logic. Once overloaded, all tasks (other than current) on the
RQ are analyzed on every push operation, even if it was previously
unpushable (due to affinity, etc). Whats more, the operation stops
at the first task that is unpushable and will not look at items
lower in the queue. This causes two problems:
1) We can have the same tasks analyzed over and over again during each
push, which extends out the fast path in the scheduler for no
gain. Consider a RQ that has dozens of tasks that are bound to a
core. Each one of those tasks will be encountered and skipped
for each push operation while they are queued.
2) There may be lower-priority tasks under the unpushable task that
could have been successfully pushed, but will never be considered
until either the unpushable task is cleared, or a pull operation
succeeds. The net result is a potential latency source for mid
priority tasks.
This patch aims to rectify these two conditions by introducing a new
priority sorted list: "pushable_tasks". A task is added to the list
each time a task is activated or preempted. It is removed from the
list any time it is deactivated, made current, or fails to push.
This works because a task only needs to be attempted to push once.
After an initial failure to push, the other cpus will eventually try to
pull the task when the conditions are proper. This also solves the
problem that we don't completely analyze all tasks due to encountering
an unpushable tasks. Now every task will have a push attempted (when
appropriate).
This reduces latency both by shorting the critical section of the
rq->lock for certain workloads, and by making sure the algorithm
considers all eligible tasks in the system.
[ rostedt: added a couple more BUG_ONs ]
Signed-off-by: Gregory Haskins <ghaskins@novell.com>
Acked-by: Steven Rostedt <srostedt@redhat.com>
2008-12-29 14:39:53 +00:00
|
|
|
#else
|
|
|
|
|
2009-01-16 13:46:40 +00:00
|
|
|
static inline void enqueue_pushable_task(struct rq *rq, struct task_struct *p)
|
2008-01-25 20:08:29 +00:00
|
|
|
{
|
2008-01-25 20:08:30 +00:00
|
|
|
}
|
|
|
|
|
2009-01-16 13:46:40 +00:00
|
|
|
static inline void dequeue_pushable_task(struct rq *rq, struct task_struct *p)
|
|
|
|
{
|
|
|
|
}
|
|
|
|
|
2009-01-14 13:55:39 +00:00
|
|
|
static inline
|
2009-01-16 13:46:40 +00:00
|
|
|
void inc_rt_migration(struct sched_rt_entity *rt_se, struct rt_rq *rt_rq)
|
|
|
|
{
|
|
|
|
}
|
|
|
|
|
2009-01-14 14:10:04 +00:00
|
|
|
static inline
|
2009-01-16 13:46:40 +00:00
|
|
|
void dec_rt_migration(struct sched_rt_entity *rt_se, struct rt_rq *rt_rq)
|
|
|
|
{
|
|
|
|
}
|
sched: create "pushable_tasks" list to limit pushing to one attempt
The RT scheduler employs a "push/pull" design to actively balance tasks
within the system (on a per disjoint cpuset basis). When a task is
awoken, it is immediately determined if there are any lower priority
cpus which should be preempted. This is opposed to the way normal
SCHED_OTHER tasks behave, which will wait for a periodic rebalancing
operation to occur before spreading out load.
When a particular RQ has more than 1 active RT task, it is said to
be in an "overloaded" state. Once this occurs, the system enters
the active balancing mode, where it will try to push the task away,
or persuade a different cpu to pull it over. The system will stay
in this state until the system falls back below the <= 1 queued RT
task per RQ.
However, the current implementation suffers from a limitation in the
push logic. Once overloaded, all tasks (other than current) on the
RQ are analyzed on every push operation, even if it was previously
unpushable (due to affinity, etc). Whats more, the operation stops
at the first task that is unpushable and will not look at items
lower in the queue. This causes two problems:
1) We can have the same tasks analyzed over and over again during each
push, which extends out the fast path in the scheduler for no
gain. Consider a RQ that has dozens of tasks that are bound to a
core. Each one of those tasks will be encountered and skipped
for each push operation while they are queued.
2) There may be lower-priority tasks under the unpushable task that
could have been successfully pushed, but will never be considered
until either the unpushable task is cleared, or a pull operation
succeeds. The net result is a potential latency source for mid
priority tasks.
This patch aims to rectify these two conditions by introducing a new
priority sorted list: "pushable_tasks". A task is added to the list
each time a task is activated or preempted. It is removed from the
list any time it is deactivated, made current, or fails to push.
This works because a task only needs to be attempted to push once.
After an initial failure to push, the other cpus will eventually try to
pull the task when the conditions are proper. This also solves the
problem that we don't completely analyze all tasks due to encountering
an unpushable tasks. Now every task will have a push attempted (when
appropriate).
This reduces latency both by shorting the critical section of the
rq->lock for certain workloads, and by making sure the algorithm
considers all eligible tasks in the system.
[ rostedt: added a couple more BUG_ONs ]
Signed-off-by: Gregory Haskins <ghaskins@novell.com>
Acked-by: Steven Rostedt <srostedt@redhat.com>
2008-12-29 14:39:53 +00:00
|
|
|
|
2018-03-03 15:27:54 +00:00
|
|
|
static inline void rt_queue_push_tasks(struct rq *rq)
|
2014-02-12 14:47:29 +00:00
|
|
|
{
|
|
|
|
}
|
2008-01-25 20:08:06 +00:00
|
|
|
#endif /* CONFIG_SMP */
|
|
|
|
|
2014-03-14 22:15:00 +00:00
|
|
|
static void enqueue_top_rt_rq(struct rt_rq *rt_rq);
|
2022-06-28 09:22:59 +00:00
|
|
|
static void dequeue_top_rt_rq(struct rt_rq *rt_rq, unsigned int count);
|
2014-03-14 22:15:00 +00:00
|
|
|
|
2008-01-25 20:08:30 +00:00
|
|
|
static inline int on_rt_rq(struct sched_rt_entity *rt_se)
|
|
|
|
{
|
2016-01-18 14:27:07 +00:00
|
|
|
return rt_se->on_rq;
|
2008-01-25 20:08:30 +00:00
|
|
|
}
|
|
|
|
|
2019-10-09 10:46:11 +00:00
|
|
|
#ifdef CONFIG_UCLAMP_TASK
|
|
|
|
/*
|
|
|
|
* Verify the fitness of task @p to run on @cpu taking into account the uclamp
|
|
|
|
* settings.
|
|
|
|
*
|
|
|
|
* This check is only important for heterogeneous systems where uclamp_min value
|
|
|
|
* is higher than the capacity of a @cpu. For non-heterogeneous system this
|
|
|
|
* function will always return true.
|
|
|
|
*
|
|
|
|
* The function will return true if the capacity of the @cpu is >= the
|
|
|
|
* uclamp_min and false otherwise.
|
|
|
|
*
|
|
|
|
* Note that uclamp_min will be clamped to uclamp_max if uclamp_min
|
|
|
|
* > uclamp_max.
|
|
|
|
*/
|
|
|
|
static inline bool rt_task_fits_capacity(struct task_struct *p, int cpu)
|
|
|
|
{
|
|
|
|
unsigned int min_cap;
|
|
|
|
unsigned int max_cap;
|
|
|
|
unsigned int cpu_cap;
|
|
|
|
|
|
|
|
/* Only heterogeneous systems can benefit from this check */
|
2022-07-29 11:13:03 +00:00
|
|
|
if (!sched_asym_cpucap_active())
|
2019-10-09 10:46:11 +00:00
|
|
|
return true;
|
|
|
|
|
|
|
|
min_cap = uclamp_eff_value(p, UCLAMP_MIN);
|
|
|
|
max_cap = uclamp_eff_value(p, UCLAMP_MAX);
|
|
|
|
|
|
|
|
cpu_cap = capacity_orig_of(cpu);
|
|
|
|
|
|
|
|
return cpu_cap >= min(min_cap, max_cap);
|
|
|
|
}
|
|
|
|
#else
|
|
|
|
static inline bool rt_task_fits_capacity(struct task_struct *p, int cpu)
|
|
|
|
{
|
|
|
|
return true;
|
|
|
|
}
|
|
|
|
#endif
|
|
|
|
|
2008-02-13 14:45:40 +00:00
|
|
|
#ifdef CONFIG_RT_GROUP_SCHED
|
2008-01-25 20:08:30 +00:00
|
|
|
|
2008-02-13 14:45:39 +00:00
|
|
|
static inline u64 sched_rt_runtime(struct rt_rq *rt_rq)
|
2008-01-25 20:08:30 +00:00
|
|
|
{
|
|
|
|
if (!rt_rq->tg)
|
2008-02-13 14:45:39 +00:00
|
|
|
return RUNTIME_INF;
|
2008-01-25 20:08:30 +00:00
|
|
|
|
2008-04-19 17:44:58 +00:00
|
|
|
return rt_rq->rt_runtime;
|
|
|
|
}
|
|
|
|
|
|
|
|
static inline u64 sched_rt_period(struct rt_rq *rt_rq)
|
|
|
|
{
|
|
|
|
return ktime_to_ns(rt_rq->tg->rt_bandwidth.rt_period);
|
2008-01-25 20:08:30 +00:00
|
|
|
}
|
|
|
|
|
2011-05-14 06:20:02 +00:00
|
|
|
typedef struct task_group *rt_rq_iter_t;
|
|
|
|
|
2011-06-28 02:51:31 +00:00
|
|
|
static inline struct task_group *next_task_group(struct task_group *tg)
|
|
|
|
{
|
|
|
|
do {
|
|
|
|
tg = list_entry_rcu(tg->list.next,
|
|
|
|
typeof(struct task_group), list);
|
|
|
|
} while (&tg->list != &task_groups && task_group_is_autogroup(tg));
|
|
|
|
|
|
|
|
if (&tg->list == &task_groups)
|
|
|
|
tg = NULL;
|
|
|
|
|
|
|
|
return tg;
|
|
|
|
}
|
|
|
|
|
|
|
|
#define for_each_rt_rq(rt_rq, iter, rq) \
|
|
|
|
for (iter = container_of(&task_groups, typeof(*iter), list); \
|
|
|
|
(iter = next_task_group(iter)) && \
|
|
|
|
(rt_rq = iter->rt_rq[cpu_of(rq)]);)
|
2011-05-14 06:20:02 +00:00
|
|
|
|
2008-01-25 20:08:30 +00:00
|
|
|
#define for_each_sched_rt_entity(rt_se) \
|
|
|
|
for (; rt_se; rt_se = rt_se->parent)
|
|
|
|
|
|
|
|
static inline struct rt_rq *group_rt_rq(struct sched_rt_entity *rt_se)
|
|
|
|
{
|
|
|
|
return rt_se->my_q;
|
|
|
|
}
|
|
|
|
|
2016-01-18 14:27:07 +00:00
|
|
|
static void enqueue_rt_entity(struct sched_rt_entity *rt_se, unsigned int flags);
|
|
|
|
static void dequeue_rt_entity(struct sched_rt_entity *rt_se, unsigned int flags);
|
2008-01-25 20:08:30 +00:00
|
|
|
|
2008-02-13 14:45:39 +00:00
|
|
|
static void sched_rt_rq_enqueue(struct rt_rq *rt_rq)
|
2008-01-25 20:08:30 +00:00
|
|
|
{
|
sched_rt.c: resch needed in rt_rq_enqueue() for the root rt_rq
While working on the new version of the code for SCHED_SPORADIC I
noticed something strange in the present throttling mechanism. More
specifically in the throttling timer handler in sched_rt.c
(do_sched_rt_period_timer()) and in rt_rq_enqueue().
The problem is that, when unthrottling a runqueue, rt_rq_enqueue() only
asks for rescheduling if the runqueue has a sched_entity associated to
it (i.e., rt_rq->rt_se != NULL).
Now, if the runqueue is the root rq (which has a rt_se = NULL)
rescheduling does not take place, and it is delayed to some undefined
instant in the future.
This imply some random bandwidth usage by the RT tasks under throttling.
For instance, setting rt_runtime_us/rt_period_us = 950ms/1000ms an RT
task will get less than 95%. In our tests we got something varying
between 70% to 95%.
Using smaller time values, e.g., 95ms/100ms, things are even worse, and
I can see values also going down to 20-25%!!
The tests we performed are simply running 'yes' as a SCHED_FIFO task,
and checking the CPU usage with top, but we can investigate thoroughly
if you think it is needed.
Things go much better, for us, with the attached patch... Don't know if
it is the best approach, but it solved the issue for us.
Signed-off-by: Dario Faggioli <raistlin@linux.it>
Signed-off-by: Michael Trimarchi <trimarchimichael@yahoo.it>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: <stable@kernel.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-10-03 15:40:46 +00:00
|
|
|
struct task_struct *curr = rq_of_rt_rq(rt_rq)->curr;
|
2014-06-28 20:03:57 +00:00
|
|
|
struct rq *rq = rq_of_rt_rq(rt_rq);
|
2010-01-29 06:57:52 +00:00
|
|
|
struct sched_rt_entity *rt_se;
|
|
|
|
|
2014-06-28 20:03:57 +00:00
|
|
|
int cpu = cpu_of(rq);
|
sched: Fix sched rt group scheduling when hierachy is enabled
The current sched rt code is broken when it comes to hierarchical
scheduling, this patch fixes two problems
1. It adds redundant enqueuing (harmless) when it finds a queue
has tasks enqueued, but it has no run time and it is not
throttled.
2. The most important change is in sched_rt_rq_enqueue/dequeue.
The code just picks the rt_rq belonging to the current cpu
on which the period timer runs, the patch fixes it, so that
the correct rt_se is enqueued/dequeued.
Tested with a simple hierarchy
/c/d, c and d assigned similar runtimes of 50,000 and a while
1 loop runs within "d". Both c and d get throttled, without
the patch, the task just stops running and never runs (depends
on where the sched_rt b/w timer runs). With the patch, the
task is throttled and runs as expected.
[ bharata, suggestions on how to pick the rt_se belong to the
rt_rq and correct cpu ]
Signed-off-by: Balbir Singh <balbir@linux.vnet.ibm.com>
Acked-by: Bharata B Rao <bharata@linux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: stable@kernel.org
LKML-Reference: <20110303113435.GA2868@balbir.in.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2011-03-03 11:34:35 +00:00
|
|
|
|
|
|
|
rt_se = rt_rq->tg->rt_se[cpu];
|
2008-01-25 20:08:30 +00:00
|
|
|
|
sched_rt.c: resch needed in rt_rq_enqueue() for the root rt_rq
While working on the new version of the code for SCHED_SPORADIC I
noticed something strange in the present throttling mechanism. More
specifically in the throttling timer handler in sched_rt.c
(do_sched_rt_period_timer()) and in rt_rq_enqueue().
The problem is that, when unthrottling a runqueue, rt_rq_enqueue() only
asks for rescheduling if the runqueue has a sched_entity associated to
it (i.e., rt_rq->rt_se != NULL).
Now, if the runqueue is the root rq (which has a rt_se = NULL)
rescheduling does not take place, and it is delayed to some undefined
instant in the future.
This imply some random bandwidth usage by the RT tasks under throttling.
For instance, setting rt_runtime_us/rt_period_us = 950ms/1000ms an RT
task will get less than 95%. In our tests we got something varying
between 70% to 95%.
Using smaller time values, e.g., 95ms/100ms, things are even worse, and
I can see values also going down to 20-25%!!
The tests we performed are simply running 'yes' as a SCHED_FIFO task,
and checking the CPU usage with top, but we can investigate thoroughly
if you think it is needed.
Things go much better, for us, with the attached patch... Don't know if
it is the best approach, but it solved the issue for us.
Signed-off-by: Dario Faggioli <raistlin@linux.it>
Signed-off-by: Michael Trimarchi <trimarchimichael@yahoo.it>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: <stable@kernel.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-10-03 15:40:46 +00:00
|
|
|
if (rt_rq->rt_nr_running) {
|
2014-03-14 22:15:00 +00:00
|
|
|
if (!rt_se)
|
|
|
|
enqueue_top_rt_rq(rt_rq);
|
|
|
|
else if (!on_rt_rq(rt_se))
|
2016-01-18 14:27:07 +00:00
|
|
|
enqueue_rt_entity(rt_se, 0);
|
2014-03-14 22:15:00 +00:00
|
|
|
|
2008-12-29 14:39:49 +00:00
|
|
|
if (rt_rq->highest_prio.curr < curr->prio)
|
2014-06-28 20:03:57 +00:00
|
|
|
resched_curr(rq);
|
2008-01-25 20:08:30 +00:00
|
|
|
}
|
|
|
|
}
|
|
|
|
|
2008-02-13 14:45:39 +00:00
|
|
|
static void sched_rt_rq_dequeue(struct rt_rq *rt_rq)
|
2008-01-25 20:08:30 +00:00
|
|
|
{
|
2010-01-29 06:57:52 +00:00
|
|
|
struct sched_rt_entity *rt_se;
|
sched: Fix sched rt group scheduling when hierachy is enabled
The current sched rt code is broken when it comes to hierarchical
scheduling, this patch fixes two problems
1. It adds redundant enqueuing (harmless) when it finds a queue
has tasks enqueued, but it has no run time and it is not
throttled.
2. The most important change is in sched_rt_rq_enqueue/dequeue.
The code just picks the rt_rq belonging to the current cpu
on which the period timer runs, the patch fixes it, so that
the correct rt_se is enqueued/dequeued.
Tested with a simple hierarchy
/c/d, c and d assigned similar runtimes of 50,000 and a while
1 loop runs within "d". Both c and d get throttled, without
the patch, the task just stops running and never runs (depends
on where the sched_rt b/w timer runs). With the patch, the
task is throttled and runs as expected.
[ bharata, suggestions on how to pick the rt_se belong to the
rt_rq and correct cpu ]
Signed-off-by: Balbir Singh <balbir@linux.vnet.ibm.com>
Acked-by: Bharata B Rao <bharata@linux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: stable@kernel.org
LKML-Reference: <20110303113435.GA2868@balbir.in.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2011-03-03 11:34:35 +00:00
|
|
|
int cpu = cpu_of(rq_of_rt_rq(rt_rq));
|
2010-01-29 06:57:52 +00:00
|
|
|
|
sched: Fix sched rt group scheduling when hierachy is enabled
The current sched rt code is broken when it comes to hierarchical
scheduling, this patch fixes two problems
1. It adds redundant enqueuing (harmless) when it finds a queue
has tasks enqueued, but it has no run time and it is not
throttled.
2. The most important change is in sched_rt_rq_enqueue/dequeue.
The code just picks the rt_rq belonging to the current cpu
on which the period timer runs, the patch fixes it, so that
the correct rt_se is enqueued/dequeued.
Tested with a simple hierarchy
/c/d, c and d assigned similar runtimes of 50,000 and a while
1 loop runs within "d". Both c and d get throttled, without
the patch, the task just stops running and never runs (depends
on where the sched_rt b/w timer runs). With the patch, the
task is throttled and runs as expected.
[ bharata, suggestions on how to pick the rt_se belong to the
rt_rq and correct cpu ]
Signed-off-by: Balbir Singh <balbir@linux.vnet.ibm.com>
Acked-by: Bharata B Rao <bharata@linux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: stable@kernel.org
LKML-Reference: <20110303113435.GA2868@balbir.in.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2011-03-03 11:34:35 +00:00
|
|
|
rt_se = rt_rq->tg->rt_se[cpu];
|
2008-01-25 20:08:30 +00:00
|
|
|
|
2018-06-26 13:53:22 +00:00
|
|
|
if (!rt_se) {
|
2022-06-28 09:22:59 +00:00
|
|
|
dequeue_top_rt_rq(rt_rq, rt_rq->rt_nr_running);
|
2018-06-26 13:53:22 +00:00
|
|
|
/* Kick cpufreq (see the comment in kernel/sched/sched.h). */
|
|
|
|
cpufreq_update_util(rq_of_rt_rq(rt_rq), 0);
|
|
|
|
}
|
2014-03-14 22:15:00 +00:00
|
|
|
else if (on_rt_rq(rt_se))
|
2016-01-18 14:27:07 +00:00
|
|
|
dequeue_rt_entity(rt_se, 0);
|
2008-01-25 20:08:30 +00:00
|
|
|
}
|
|
|
|
|
2014-03-14 22:15:07 +00:00
|
|
|
static inline int rt_rq_throttled(struct rt_rq *rt_rq)
|
|
|
|
{
|
|
|
|
return rt_rq->rt_throttled && !rt_rq->rt_nr_boosted;
|
|
|
|
}
|
|
|
|
|
2008-02-13 14:45:39 +00:00
|
|
|
static int rt_se_boosted(struct sched_rt_entity *rt_se)
|
|
|
|
{
|
|
|
|
struct rt_rq *rt_rq = group_rt_rq(rt_se);
|
|
|
|
struct task_struct *p;
|
|
|
|
|
|
|
|
if (rt_rq)
|
|
|
|
return !!rt_rq->rt_nr_boosted;
|
|
|
|
|
|
|
|
p = rt_task_of(rt_se);
|
|
|
|
return p->prio != p->normal_prio;
|
|
|
|
}
|
|
|
|
|
2008-04-19 17:44:57 +00:00
|
|
|
#ifdef CONFIG_SMP
|
2008-11-24 16:05:05 +00:00
|
|
|
static inline const struct cpumask *sched_rt_period_mask(void)
|
2008-04-19 17:44:57 +00:00
|
|
|
{
|
2013-05-09 16:24:03 +00:00
|
|
|
return this_rq()->rd->span;
|
2008-04-19 17:44:57 +00:00
|
|
|
}
|
2008-01-25 20:08:30 +00:00
|
|
|
#else
|
2008-11-24 16:05:05 +00:00
|
|
|
static inline const struct cpumask *sched_rt_period_mask(void)
|
2008-04-19 17:44:57 +00:00
|
|
|
{
|
2008-11-24 16:05:05 +00:00
|
|
|
return cpu_online_mask;
|
2008-04-19 17:44:57 +00:00
|
|
|
}
|
|
|
|
#endif
|
2008-01-25 20:08:30 +00:00
|
|
|
|
2008-04-19 17:44:57 +00:00
|
|
|
static inline
|
|
|
|
struct rt_rq *sched_rt_period_rt_rq(struct rt_bandwidth *rt_b, int cpu)
|
2008-01-25 20:08:30 +00:00
|
|
|
{
|
2008-04-19 17:44:57 +00:00
|
|
|
return container_of(rt_b, struct task_group, rt_bandwidth)->rt_rq[cpu];
|
|
|
|
}
|
2008-02-13 14:45:39 +00:00
|
|
|
|
2008-04-19 17:44:58 +00:00
|
|
|
static inline struct rt_bandwidth *sched_rt_bandwidth(struct rt_rq *rt_rq)
|
|
|
|
{
|
|
|
|
return &rt_rq->tg->rt_bandwidth;
|
|
|
|
}
|
|
|
|
|
2008-06-24 18:09:43 +00:00
|
|
|
#else /* !CONFIG_RT_GROUP_SCHED */
|
2008-04-19 17:44:57 +00:00
|
|
|
|
|
|
|
static inline u64 sched_rt_runtime(struct rt_rq *rt_rq)
|
|
|
|
{
|
2008-04-19 17:44:58 +00:00
|
|
|
return rt_rq->rt_runtime;
|
|
|
|
}
|
|
|
|
|
|
|
|
static inline u64 sched_rt_period(struct rt_rq *rt_rq)
|
|
|
|
{
|
|
|
|
return ktime_to_ns(def_rt_bandwidth.rt_period);
|
2008-01-25 20:08:30 +00:00
|
|
|
}
|
|
|
|
|
2011-05-14 06:20:02 +00:00
|
|
|
typedef struct rt_rq *rt_rq_iter_t;
|
|
|
|
|
|
|
|
#define for_each_rt_rq(rt_rq, iter, rq) \
|
|
|
|
for ((void) iter, rt_rq = &rq->rt; rt_rq; rt_rq = NULL)
|
|
|
|
|
2008-01-25 20:08:30 +00:00
|
|
|
#define for_each_sched_rt_entity(rt_se) \
|
|
|
|
for (; rt_se; rt_se = NULL)
|
|
|
|
|
|
|
|
static inline struct rt_rq *group_rt_rq(struct sched_rt_entity *rt_se)
|
|
|
|
{
|
|
|
|
return NULL;
|
|
|
|
}
|
|
|
|
|
2008-02-13 14:45:39 +00:00
|
|
|
static inline void sched_rt_rq_enqueue(struct rt_rq *rt_rq)
|
2008-01-25 20:08:30 +00:00
|
|
|
{
|
2014-03-14 22:15:00 +00:00
|
|
|
struct rq *rq = rq_of_rt_rq(rt_rq);
|
|
|
|
|
|
|
|
if (!rt_rq->rt_nr_running)
|
|
|
|
return;
|
|
|
|
|
|
|
|
enqueue_top_rt_rq(rt_rq);
|
2014-06-28 20:03:57 +00:00
|
|
|
resched_curr(rq);
|
2008-01-25 20:08:30 +00:00
|
|
|
}
|
|
|
|
|
2008-02-13 14:45:39 +00:00
|
|
|
static inline void sched_rt_rq_dequeue(struct rt_rq *rt_rq)
|
2008-01-25 20:08:30 +00:00
|
|
|
{
|
2022-06-28 09:22:59 +00:00
|
|
|
dequeue_top_rt_rq(rt_rq, rt_rq->rt_nr_running);
|
2008-01-25 20:08:30 +00:00
|
|
|
}
|
|
|
|
|
2014-03-14 22:15:07 +00:00
|
|
|
static inline int rt_rq_throttled(struct rt_rq *rt_rq)
|
|
|
|
{
|
|
|
|
return rt_rq->rt_throttled;
|
|
|
|
}
|
|
|
|
|
2008-11-24 16:05:05 +00:00
|
|
|
static inline const struct cpumask *sched_rt_period_mask(void)
|
2008-04-19 17:44:57 +00:00
|
|
|
{
|
2008-11-24 16:05:05 +00:00
|
|
|
return cpu_online_mask;
|
2008-04-19 17:44:57 +00:00
|
|
|
}
|
|
|
|
|
|
|
|
static inline
|
|
|
|
struct rt_rq *sched_rt_period_rt_rq(struct rt_bandwidth *rt_b, int cpu)
|
|
|
|
{
|
|
|
|
return &cpu_rq(cpu)->rt;
|
|
|
|
}
|
|
|
|
|
2008-04-19 17:44:58 +00:00
|
|
|
static inline struct rt_bandwidth *sched_rt_bandwidth(struct rt_rq *rt_rq)
|
|
|
|
{
|
|
|
|
return &def_rt_bandwidth;
|
|
|
|
}
|
|
|
|
|
2008-06-24 18:09:43 +00:00
|
|
|
#endif /* CONFIG_RT_GROUP_SCHED */
|
2008-04-19 17:44:57 +00:00
|
|
|
|
sched/deadline: Prevent rt_time growth to infinity
Kirill Tkhai noted:
Since deadline tasks share rt bandwidth, we must care about
bandwidth timer set. Otherwise rt_time may grow up to infinity
in update_curr_dl(), if there are no other available RT tasks
on top level bandwidth.
RT task were in fact throttled right after they got enqueued,
and never executed again (rt_time never again went below rt_runtime).
Peter then proposed to accrue DL execution on rt_time only when
rt timer is active, and proposed a patch (this patch is a slight
modification of that) to implement that behavior. While this
solves Kirill problem, it has a drawback.
Indeed, Kirill noted again:
It looks we may get into a situation, when all CPU time is shared
between RT and DL tasks:
rt_runtime = n
rt_period = 2n
| RT working, DL sleeping | DL working, RT sleeping |
-----------------------------------------------------------
| (1) duration = n | (2) duration = n | (repeat)
|--------------------------|------------------------------|
| (rt_bw timer is running) | (rt_bw timer is not running) |
No time for fair tasks at all.
While this can happen during the first period, if rq is always backlogged,
RT tasks won't have the opportunity to execute anymore: rt_time reached
rt_runtime during (1), suppose after (2) RT is enqueued back, it gets
throttled since rt timer didn't fire, replenishment is from now on eaten up
by DL tasks that accrue their execution on rt_time (while rt timer is
active - we have an RT task waiting for replenishment). FAIR tasks are
not touched after this first period. Ok, this is not ideal, and the situation
is even worse!
What above (the nice case), practically never happens in reality, where
your rt timer is not aligned to tasks periods, tasks are in general not
periodic, etc.. Long story short, you always risk to overload your system.
This patch is based on Peter's idea, but exploits an additional fact:
if you don't have RT tasks enqueued, it makes little sense to continue
incrementing rt_time once you reached the upper limit (DL tasks have their
own mechanism for throttling).
This cures both problems:
- no matter how many DL instances in the past, you'll have an rt_time
slightly above rt_runtime when an RT task is enqueued, and from that
point on (after the first replenishment), the task will normally execute;
- you can still eat up all bandwidth during the first period, but not
anymore after that, remember that DL execution will increment rt_time
till the upper limit is reached.
The situation is still not perfect! But, we have a simple solution for now,
that limits how much you can jeopardize your system, as we keep working
towards the right answer: RT groups scheduled using deadline servers.
Reported-by: Kirill Tkhai <tkhai@yandex.ru>
Signed-off-by: Juri Lelli <juri.lelli@gmail.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Link: http://lkml.kernel.org/r/20140225151515.617714e2f2cd6c558531ba61@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2014-02-21 10:37:15 +00:00
|
|
|
bool sched_rt_bandwidth_account(struct rt_rq *rt_rq)
|
|
|
|
{
|
|
|
|
struct rt_bandwidth *rt_b = sched_rt_bandwidth(rt_rq);
|
|
|
|
|
|
|
|
return (hrtimer_active(&rt_b->rt_period_timer) ||
|
|
|
|
rt_rq->rt_time < rt_b->rt_runtime);
|
|
|
|
}
|
|
|
|
|
2008-04-19 17:44:58 +00:00
|
|
|
#ifdef CONFIG_SMP
|
2008-09-23 13:33:43 +00:00
|
|
|
/*
|
|
|
|
* We ran out of runtime, see if we can borrow some from our neighbours.
|
|
|
|
*/
|
2015-09-02 10:01:36 +00:00
|
|
|
static void do_balance_runtime(struct rt_rq *rt_rq)
|
2008-04-19 17:44:58 +00:00
|
|
|
{
|
|
|
|
struct rt_bandwidth *rt_b = sched_rt_bandwidth(rt_rq);
|
2013-01-14 17:55:31 +00:00
|
|
|
struct root_domain *rd = rq_of_rt_rq(rt_rq)->rd;
|
2015-09-02 10:01:36 +00:00
|
|
|
int i, weight;
|
2008-04-19 17:44:58 +00:00
|
|
|
u64 rt_period;
|
|
|
|
|
2008-11-24 16:05:05 +00:00
|
|
|
weight = cpumask_weight(rd->span);
|
2008-04-19 17:44:58 +00:00
|
|
|
|
2009-11-17 14:32:06 +00:00
|
|
|
raw_spin_lock(&rt_b->rt_runtime_lock);
|
2008-04-19 17:44:58 +00:00
|
|
|
rt_period = ktime_to_ns(rt_b->rt_period);
|
2008-11-24 16:05:05 +00:00
|
|
|
for_each_cpu(i, rd->span) {
|
2008-04-19 17:44:58 +00:00
|
|
|
struct rt_rq *iter = sched_rt_period_rt_rq(rt_b, i);
|
|
|
|
s64 diff;
|
|
|
|
|
|
|
|
if (iter == rt_rq)
|
|
|
|
continue;
|
|
|
|
|
2009-11-17 14:32:06 +00:00
|
|
|
raw_spin_lock(&iter->rt_runtime_lock);
|
2008-09-23 13:33:43 +00:00
|
|
|
/*
|
|
|
|
* Either all rqs have inf runtime and there's nothing to steal
|
|
|
|
* or __disable_runtime() below sets a specific rq to inf to
|
2021-03-18 12:38:50 +00:00
|
|
|
* indicate its been disabled and disallow stealing.
|
2008-09-23 13:33:43 +00:00
|
|
|
*/
|
2008-06-05 12:49:58 +00:00
|
|
|
if (iter->rt_runtime == RUNTIME_INF)
|
|
|
|
goto next;
|
|
|
|
|
2008-09-23 13:33:43 +00:00
|
|
|
/*
|
|
|
|
* From runqueues with spare time, take 1/n part of their
|
|
|
|
* spare time, but no more than our period.
|
|
|
|
*/
|
2008-04-19 17:44:58 +00:00
|
|
|
diff = iter->rt_runtime - iter->rt_time;
|
|
|
|
if (diff > 0) {
|
2008-07-24 10:43:13 +00:00
|
|
|
diff = div_u64((u64)diff, weight);
|
2008-04-19 17:44:58 +00:00
|
|
|
if (rt_rq->rt_runtime + diff > rt_period)
|
|
|
|
diff = rt_period - rt_rq->rt_runtime;
|
|
|
|
iter->rt_runtime -= diff;
|
|
|
|
rt_rq->rt_runtime += diff;
|
|
|
|
if (rt_rq->rt_runtime == rt_period) {
|
2009-11-17 14:32:06 +00:00
|
|
|
raw_spin_unlock(&iter->rt_runtime_lock);
|
2008-04-19 17:44:58 +00:00
|
|
|
break;
|
|
|
|
}
|
|
|
|
}
|
2008-06-05 12:49:58 +00:00
|
|
|
next:
|
2009-11-17 14:32:06 +00:00
|
|
|
raw_spin_unlock(&iter->rt_runtime_lock);
|
2008-04-19 17:44:58 +00:00
|
|
|
}
|
2009-11-17 14:32:06 +00:00
|
|
|
raw_spin_unlock(&rt_b->rt_runtime_lock);
|
2008-04-19 17:44:58 +00:00
|
|
|
}
|
2008-06-05 12:49:58 +00:00
|
|
|
|
2008-09-23 13:33:43 +00:00
|
|
|
/*
|
|
|
|
* Ensure this RQ takes back all the runtime it lend to its neighbours.
|
|
|
|
*/
|
2008-06-05 12:49:58 +00:00
|
|
|
static void __disable_runtime(struct rq *rq)
|
|
|
|
{
|
|
|
|
struct root_domain *rd = rq->rd;
|
2011-05-14 06:20:02 +00:00
|
|
|
rt_rq_iter_t iter;
|
2008-06-05 12:49:58 +00:00
|
|
|
struct rt_rq *rt_rq;
|
|
|
|
|
|
|
|
if (unlikely(!scheduler_running))
|
|
|
|
return;
|
|
|
|
|
2011-05-14 06:20:02 +00:00
|
|
|
for_each_rt_rq(rt_rq, iter, rq) {
|
2008-06-05 12:49:58 +00:00
|
|
|
struct rt_bandwidth *rt_b = sched_rt_bandwidth(rt_rq);
|
|
|
|
s64 want;
|
|
|
|
int i;
|
|
|
|
|
2009-11-17 14:32:06 +00:00
|
|
|
raw_spin_lock(&rt_b->rt_runtime_lock);
|
|
|
|
raw_spin_lock(&rt_rq->rt_runtime_lock);
|
2008-09-23 13:33:43 +00:00
|
|
|
/*
|
|
|
|
* Either we're all inf and nobody needs to borrow, or we're
|
|
|
|
* already disabled and thus have nothing to do, or we have
|
|
|
|
* exactly the right amount of runtime to take out.
|
|
|
|
*/
|
2008-06-05 12:49:58 +00:00
|
|
|
if (rt_rq->rt_runtime == RUNTIME_INF ||
|
|
|
|
rt_rq->rt_runtime == rt_b->rt_runtime)
|
|
|
|
goto balanced;
|
2009-11-17 14:32:06 +00:00
|
|
|
raw_spin_unlock(&rt_rq->rt_runtime_lock);
|
2008-06-05 12:49:58 +00:00
|
|
|
|
2008-09-23 13:33:43 +00:00
|
|
|
/*
|
|
|
|
* Calculate the difference between what we started out with
|
|
|
|
* and what we current have, that's the amount of runtime
|
|
|
|
* we lend and now have to reclaim.
|
|
|
|
*/
|
2008-06-05 12:49:58 +00:00
|
|
|
want = rt_b->rt_runtime - rt_rq->rt_runtime;
|
|
|
|
|
2008-09-23 13:33:43 +00:00
|
|
|
/*
|
|
|
|
* Greedy reclaim, take back as much as we can.
|
|
|
|
*/
|
2008-11-24 16:05:05 +00:00
|
|
|
for_each_cpu(i, rd->span) {
|
2008-06-05 12:49:58 +00:00
|
|
|
struct rt_rq *iter = sched_rt_period_rt_rq(rt_b, i);
|
|
|
|
s64 diff;
|
|
|
|
|
2008-09-23 13:33:43 +00:00
|
|
|
/*
|
|
|
|
* Can't reclaim from ourselves or disabled runqueues.
|
|
|
|
*/
|
2008-08-14 13:49:00 +00:00
|
|
|
if (iter == rt_rq || iter->rt_runtime == RUNTIME_INF)
|
2008-06-05 12:49:58 +00:00
|
|
|
continue;
|
|
|
|
|
2009-11-17 14:32:06 +00:00
|
|
|
raw_spin_lock(&iter->rt_runtime_lock);
|
2008-06-05 12:49:58 +00:00
|
|
|
if (want > 0) {
|
|
|
|
diff = min_t(s64, iter->rt_runtime, want);
|
|
|
|
iter->rt_runtime -= diff;
|
|
|
|
want -= diff;
|
|
|
|
} else {
|
|
|
|
iter->rt_runtime -= want;
|
|
|
|
want -= want;
|
|
|
|
}
|
2009-11-17 14:32:06 +00:00
|
|
|
raw_spin_unlock(&iter->rt_runtime_lock);
|
2008-06-05 12:49:58 +00:00
|
|
|
|
|
|
|
if (!want)
|
|
|
|
break;
|
|
|
|
}
|
|
|
|
|
2009-11-17 14:32:06 +00:00
|
|
|
raw_spin_lock(&rt_rq->rt_runtime_lock);
|
2008-09-23 13:33:43 +00:00
|
|
|
/*
|
|
|
|
* We cannot be left wanting - that would mean some runtime
|
|
|
|
* leaked out of the system.
|
|
|
|
*/
|
2022-08-11 06:54:52 +00:00
|
|
|
WARN_ON_ONCE(want);
|
2008-06-05 12:49:58 +00:00
|
|
|
balanced:
|
2008-09-23 13:33:43 +00:00
|
|
|
/*
|
|
|
|
* Disable all the borrow logic by pretending we have inf
|
|
|
|
* runtime - in which case borrowing doesn't make sense.
|
|
|
|
*/
|
2008-06-05 12:49:58 +00:00
|
|
|
rt_rq->rt_runtime = RUNTIME_INF;
|
2012-08-09 22:34:47 +00:00
|
|
|
rt_rq->rt_throttled = 0;
|
2009-11-17 14:32:06 +00:00
|
|
|
raw_spin_unlock(&rt_rq->rt_runtime_lock);
|
|
|
|
raw_spin_unlock(&rt_b->rt_runtime_lock);
|
2014-06-25 08:19:48 +00:00
|
|
|
|
|
|
|
/* Make rt_rq available for pick_next_task() */
|
|
|
|
sched_rt_rq_enqueue(rt_rq);
|
2008-06-05 12:49:58 +00:00
|
|
|
}
|
|
|
|
}
|
|
|
|
|
|
|
|
static void __enable_runtime(struct rq *rq)
|
|
|
|
{
|
2011-05-14 06:20:02 +00:00
|
|
|
rt_rq_iter_t iter;
|
2008-06-05 12:49:58 +00:00
|
|
|
struct rt_rq *rt_rq;
|
|
|
|
|
|
|
|
if (unlikely(!scheduler_running))
|
|
|
|
return;
|
|
|
|
|
2008-09-23 13:33:43 +00:00
|
|
|
/*
|
|
|
|
* Reset each runqueue's bandwidth settings
|
|
|
|
*/
|
2011-05-14 06:20:02 +00:00
|
|
|
for_each_rt_rq(rt_rq, iter, rq) {
|
2008-06-05 12:49:58 +00:00
|
|
|
struct rt_bandwidth *rt_b = sched_rt_bandwidth(rt_rq);
|
|
|
|
|
2009-11-17 14:32:06 +00:00
|
|
|
raw_spin_lock(&rt_b->rt_runtime_lock);
|
|
|
|
raw_spin_lock(&rt_rq->rt_runtime_lock);
|
2008-06-05 12:49:58 +00:00
|
|
|
rt_rq->rt_runtime = rt_b->rt_runtime;
|
|
|
|
rt_rq->rt_time = 0;
|
2008-09-09 03:26:33 +00:00
|
|
|
rt_rq->rt_throttled = 0;
|
2009-11-17 14:32:06 +00:00
|
|
|
raw_spin_unlock(&rt_rq->rt_runtime_lock);
|
|
|
|
raw_spin_unlock(&rt_b->rt_runtime_lock);
|
2008-06-05 12:49:58 +00:00
|
|
|
}
|
|
|
|
}
|
|
|
|
|
2015-09-02 10:01:36 +00:00
|
|
|
static void balance_runtime(struct rt_rq *rt_rq)
|
2008-06-19 12:22:26 +00:00
|
|
|
{
|
2011-10-06 20:39:14 +00:00
|
|
|
if (!sched_feat(RT_RUNTIME_SHARE))
|
2015-09-02 10:01:36 +00:00
|
|
|
return;
|
2011-10-06 20:39:14 +00:00
|
|
|
|
2008-06-19 12:22:26 +00:00
|
|
|
if (rt_rq->rt_time > rt_rq->rt_runtime) {
|
2009-11-17 14:32:06 +00:00
|
|
|
raw_spin_unlock(&rt_rq->rt_runtime_lock);
|
2015-09-02 10:01:36 +00:00
|
|
|
do_balance_runtime(rt_rq);
|
2009-11-17 14:32:06 +00:00
|
|
|
raw_spin_lock(&rt_rq->rt_runtime_lock);
|
2008-06-19 12:22:26 +00:00
|
|
|
}
|
|
|
|
}
|
2008-06-24 18:09:43 +00:00
|
|
|
#else /* !CONFIG_SMP */
|
2015-09-02 10:01:36 +00:00
|
|
|
static inline void balance_runtime(struct rt_rq *rt_rq) {}
|
2008-06-24 18:09:43 +00:00
|
|
|
#endif /* CONFIG_SMP */
|
2008-04-19 17:44:58 +00:00
|
|
|
|
2008-06-19 12:22:26 +00:00
|
|
|
static int do_sched_rt_period_timer(struct rt_bandwidth *rt_b, int overrun)
|
|
|
|
{
|
2011-10-18 20:03:48 +00:00
|
|
|
int i, idle = 1, throttled = 0;
|
2008-11-24 16:05:05 +00:00
|
|
|
const struct cpumask *span;
|
2008-06-19 12:22:26 +00:00
|
|
|
|
|
|
|
span = sched_rt_period_mask();
|
2012-08-07 08:02:38 +00:00
|
|
|
#ifdef CONFIG_RT_GROUP_SCHED
|
|
|
|
/*
|
|
|
|
* FIXME: isolated CPUs should really leave the root task group,
|
|
|
|
* whether they are isolcpus or were isolated via cpusets, lest
|
|
|
|
* the timer run on a CPU which does not service all runqueues,
|
|
|
|
* potentially leaving other CPUs indefinitely throttled. If
|
|
|
|
* isolation is really required, the user will turn the throttle
|
|
|
|
* off to kill the perturbations it causes anyway. Meanwhile,
|
|
|
|
* this maintains functionality for boot and/or troubleshooting.
|
|
|
|
*/
|
|
|
|
if (rt_b == &root_task_group.rt_bandwidth)
|
|
|
|
span = cpu_online_mask;
|
|
|
|
#endif
|
2008-11-24 16:05:05 +00:00
|
|
|
for_each_cpu(i, span) {
|
2008-06-19 12:22:26 +00:00
|
|
|
int enqueue = 0;
|
|
|
|
struct rt_rq *rt_rq = sched_rt_period_rt_rq(rt_b, i);
|
|
|
|
struct rq *rq = rq_of_rt_rq(rt_rq);
|
sched/core: Avoid obvious double update_rq_clock warning
When we use raw_spin_rq_lock() to acquire the rq lock and have to
update the rq clock while holding the lock, the kernel may issue
a WARN_DOUBLE_CLOCK warning.
Since we directly use raw_spin_rq_lock() to acquire rq lock instead of
rq_lock(), there is no corresponding change to rq->clock_update_flags.
In particular, we have obtained the rq lock of other CPUs, the
rq->clock_update_flags of this CPU may be RQCF_UPDATED at this time, and
then calling update_rq_clock() will trigger the WARN_DOUBLE_CLOCK warning.
So we need to clear RQCF_UPDATED of rq->clock_update_flags to avoid
the WARN_DOUBLE_CLOCK warning.
For the sched_rt_period_timer() and migrate_task_rq_dl() cases
we simply replace raw_spin_rq_lock()/raw_spin_rq_unlock() with
rq_lock()/rq_unlock().
For the {pull,push}_{rt,dl}_task() cases, we add the
double_rq_clock_clear_update() function to clear RQCF_UPDATED of
rq->clock_update_flags, and call double_rq_clock_clear_update()
before double_lock_balance()/double_rq_lock() returns to avoid the
WARN_DOUBLE_CLOCK warning.
Some call trace reports:
Call Trace 1:
<IRQ>
sched_rt_period_timer+0x10f/0x3a0
? enqueue_top_rt_rq+0x110/0x110
__hrtimer_run_queues+0x1a9/0x490
hrtimer_interrupt+0x10b/0x240
__sysvec_apic_timer_interrupt+0x8a/0x250
sysvec_apic_timer_interrupt+0x9a/0xd0
</IRQ>
<TASK>
asm_sysvec_apic_timer_interrupt+0x12/0x20
Call Trace 2:
<TASK>
activate_task+0x8b/0x110
push_rt_task.part.108+0x241/0x2c0
push_rt_tasks+0x15/0x30
finish_task_switch+0xaa/0x2e0
? __switch_to+0x134/0x420
__schedule+0x343/0x8e0
? hrtimer_start_range_ns+0x101/0x340
schedule+0x4e/0xb0
do_nanosleep+0x8e/0x160
hrtimer_nanosleep+0x89/0x120
? hrtimer_init_sleeper+0x90/0x90
__x64_sys_nanosleep+0x96/0xd0
do_syscall_64+0x34/0x90
entry_SYSCALL_64_after_hwframe+0x44/0xae
Call Trace 3:
<TASK>
deactivate_task+0x93/0xe0
pull_rt_task+0x33e/0x400
balance_rt+0x7e/0x90
__schedule+0x62f/0x8e0
do_task_dead+0x3f/0x50
do_exit+0x7b8/0xbb0
do_group_exit+0x2d/0x90
get_signal+0x9df/0x9e0
? preempt_count_add+0x56/0xa0
? __remove_hrtimer+0x35/0x70
arch_do_signal_or_restart+0x36/0x720
? nanosleep_copyout+0x39/0x50
? do_nanosleep+0x131/0x160
? audit_filter_inodes+0xf5/0x120
exit_to_user_mode_prepare+0x10f/0x1e0
syscall_exit_to_user_mode+0x17/0x30
do_syscall_64+0x40/0x90
entry_SYSCALL_64_after_hwframe+0x44/0xae
Call Trace 4:
update_rq_clock+0x128/0x1a0
migrate_task_rq_dl+0xec/0x310
set_task_cpu+0x84/0x1e4
try_to_wake_up+0x1d8/0x5c0
wake_up_process+0x1c/0x30
hrtimer_wakeup+0x24/0x3c
__hrtimer_run_queues+0x114/0x270
hrtimer_interrupt+0xe8/0x244
arch_timer_handler_phys+0x30/0x50
handle_percpu_devid_irq+0x88/0x140
generic_handle_domain_irq+0x40/0x60
gic_handle_irq+0x48/0xe0
call_on_irq_stack+0x2c/0x60
do_interrupt_handler+0x80/0x84
Steps to reproduce:
1. Enable CONFIG_SCHED_DEBUG when compiling the kernel
2. echo 1 > /sys/kernel/debug/clear_warn_once
echo "WARN_DOUBLE_CLOCK" > /sys/kernel/debug/sched/features
echo "NO_RT_PUSH_IPI" > /sys/kernel/debug/sched/features
3. Run some rt/dl tasks that periodically work and sleep, e.g.
Create 2*n rt or dl (90% running) tasks via rt-app (on a system
with n CPUs), and Dietmar Eggemann reports Call Trace 4 when running
on PREEMPT_RT kernel.
Signed-off-by: Hao Jia <jiahao.os@bytedance.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Link: https://lore.kernel.org/r/20220430085843.62939-2-jiahao.os@bytedance.com
2022-04-30 08:58:42 +00:00
|
|
|
struct rq_flags rf;
|
2017-05-15 19:14:13 +00:00
|
|
|
int skip;
|
|
|
|
|
|
|
|
/*
|
|
|
|
* When span == cpu_online_mask, taking each rq->lock
|
|
|
|
* can be time-consuming. Try to avoid it when possible.
|
|
|
|
*/
|
|
|
|
raw_spin_lock(&rt_rq->rt_runtime_lock);
|
2018-07-18 00:46:55 +00:00
|
|
|
if (!sched_feat(RT_RUNTIME_SHARE) && rt_rq->rt_runtime != RUNTIME_INF)
|
|
|
|
rt_rq->rt_runtime = rt_b->rt_runtime;
|
2017-05-15 19:14:13 +00:00
|
|
|
skip = !rt_rq->rt_time && !rt_rq->rt_nr_running;
|
|
|
|
raw_spin_unlock(&rt_rq->rt_runtime_lock);
|
|
|
|
if (skip)
|
|
|
|
continue;
|
2008-06-19 12:22:26 +00:00
|
|
|
|
sched/core: Avoid obvious double update_rq_clock warning
When we use raw_spin_rq_lock() to acquire the rq lock and have to
update the rq clock while holding the lock, the kernel may issue
a WARN_DOUBLE_CLOCK warning.
Since we directly use raw_spin_rq_lock() to acquire rq lock instead of
rq_lock(), there is no corresponding change to rq->clock_update_flags.
In particular, we have obtained the rq lock of other CPUs, the
rq->clock_update_flags of this CPU may be RQCF_UPDATED at this time, and
then calling update_rq_clock() will trigger the WARN_DOUBLE_CLOCK warning.
So we need to clear RQCF_UPDATED of rq->clock_update_flags to avoid
the WARN_DOUBLE_CLOCK warning.
For the sched_rt_period_timer() and migrate_task_rq_dl() cases
we simply replace raw_spin_rq_lock()/raw_spin_rq_unlock() with
rq_lock()/rq_unlock().
For the {pull,push}_{rt,dl}_task() cases, we add the
double_rq_clock_clear_update() function to clear RQCF_UPDATED of
rq->clock_update_flags, and call double_rq_clock_clear_update()
before double_lock_balance()/double_rq_lock() returns to avoid the
WARN_DOUBLE_CLOCK warning.
Some call trace reports:
Call Trace 1:
<IRQ>
sched_rt_period_timer+0x10f/0x3a0
? enqueue_top_rt_rq+0x110/0x110
__hrtimer_run_queues+0x1a9/0x490
hrtimer_interrupt+0x10b/0x240
__sysvec_apic_timer_interrupt+0x8a/0x250
sysvec_apic_timer_interrupt+0x9a/0xd0
</IRQ>
<TASK>
asm_sysvec_apic_timer_interrupt+0x12/0x20
Call Trace 2:
<TASK>
activate_task+0x8b/0x110
push_rt_task.part.108+0x241/0x2c0
push_rt_tasks+0x15/0x30
finish_task_switch+0xaa/0x2e0
? __switch_to+0x134/0x420
__schedule+0x343/0x8e0
? hrtimer_start_range_ns+0x101/0x340
schedule+0x4e/0xb0
do_nanosleep+0x8e/0x160
hrtimer_nanosleep+0x89/0x120
? hrtimer_init_sleeper+0x90/0x90
__x64_sys_nanosleep+0x96/0xd0
do_syscall_64+0x34/0x90
entry_SYSCALL_64_after_hwframe+0x44/0xae
Call Trace 3:
<TASK>
deactivate_task+0x93/0xe0
pull_rt_task+0x33e/0x400
balance_rt+0x7e/0x90
__schedule+0x62f/0x8e0
do_task_dead+0x3f/0x50
do_exit+0x7b8/0xbb0
do_group_exit+0x2d/0x90
get_signal+0x9df/0x9e0
? preempt_count_add+0x56/0xa0
? __remove_hrtimer+0x35/0x70
arch_do_signal_or_restart+0x36/0x720
? nanosleep_copyout+0x39/0x50
? do_nanosleep+0x131/0x160
? audit_filter_inodes+0xf5/0x120
exit_to_user_mode_prepare+0x10f/0x1e0
syscall_exit_to_user_mode+0x17/0x30
do_syscall_64+0x40/0x90
entry_SYSCALL_64_after_hwframe+0x44/0xae
Call Trace 4:
update_rq_clock+0x128/0x1a0
migrate_task_rq_dl+0xec/0x310
set_task_cpu+0x84/0x1e4
try_to_wake_up+0x1d8/0x5c0
wake_up_process+0x1c/0x30
hrtimer_wakeup+0x24/0x3c
__hrtimer_run_queues+0x114/0x270
hrtimer_interrupt+0xe8/0x244
arch_timer_handler_phys+0x30/0x50
handle_percpu_devid_irq+0x88/0x140
generic_handle_domain_irq+0x40/0x60
gic_handle_irq+0x48/0xe0
call_on_irq_stack+0x2c/0x60
do_interrupt_handler+0x80/0x84
Steps to reproduce:
1. Enable CONFIG_SCHED_DEBUG when compiling the kernel
2. echo 1 > /sys/kernel/debug/clear_warn_once
echo "WARN_DOUBLE_CLOCK" > /sys/kernel/debug/sched/features
echo "NO_RT_PUSH_IPI" > /sys/kernel/debug/sched/features
3. Run some rt/dl tasks that periodically work and sleep, e.g.
Create 2*n rt or dl (90% running) tasks via rt-app (on a system
with n CPUs), and Dietmar Eggemann reports Call Trace 4 when running
on PREEMPT_RT kernel.
Signed-off-by: Hao Jia <jiahao.os@bytedance.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Link: https://lore.kernel.org/r/20220430085843.62939-2-jiahao.os@bytedance.com
2022-04-30 08:58:42 +00:00
|
|
|
rq_lock(rq, &rf);
|
2018-04-02 16:49:54 +00:00
|
|
|
update_rq_clock(rq);
|
|
|
|
|
2008-06-19 12:22:26 +00:00
|
|
|
if (rt_rq->rt_time) {
|
|
|
|
u64 runtime;
|
|
|
|
|
2009-11-17 14:32:06 +00:00
|
|
|
raw_spin_lock(&rt_rq->rt_runtime_lock);
|
2008-06-19 12:22:26 +00:00
|
|
|
if (rt_rq->rt_throttled)
|
|
|
|
balance_runtime(rt_rq);
|
|
|
|
runtime = rt_rq->rt_runtime;
|
|
|
|
rt_rq->rt_time -= min(rt_rq->rt_time, overrun*runtime);
|
|
|
|
if (rt_rq->rt_throttled && rt_rq->rt_time < runtime) {
|
|
|
|
rt_rq->rt_throttled = 0;
|
|
|
|
enqueue = 1;
|
2011-04-29 06:36:50 +00:00
|
|
|
|
|
|
|
/*
|
2015-01-05 10:18:11 +00:00
|
|
|
* When we're idle and a woken (rt) task is
|
|
|
|
* throttled check_preempt_curr() will set
|
|
|
|
* skip_update and the time between the wakeup
|
|
|
|
* and this unthrottle will get accounted as
|
|
|
|
* 'runtime'.
|
2011-04-29 06:36:50 +00:00
|
|
|
*/
|
|
|
|
if (rt_rq->rt_nr_running && rq->curr == rq->idle)
|
2018-04-04 16:15:39 +00:00
|
|
|
rq_clock_cancel_skipupdate(rq);
|
2008-06-19 12:22:26 +00:00
|
|
|
}
|
|
|
|
if (rt_rq->rt_time || rt_rq->rt_nr_running)
|
|
|
|
idle = 0;
|
2009-11-17 14:32:06 +00:00
|
|
|
raw_spin_unlock(&rt_rq->rt_runtime_lock);
|
sched: Fix sched rt group scheduling when hierachy is enabled
The current sched rt code is broken when it comes to hierarchical
scheduling, this patch fixes two problems
1. It adds redundant enqueuing (harmless) when it finds a queue
has tasks enqueued, but it has no run time and it is not
throttled.
2. The most important change is in sched_rt_rq_enqueue/dequeue.
The code just picks the rt_rq belonging to the current cpu
on which the period timer runs, the patch fixes it, so that
the correct rt_se is enqueued/dequeued.
Tested with a simple hierarchy
/c/d, c and d assigned similar runtimes of 50,000 and a while
1 loop runs within "d". Both c and d get throttled, without
the patch, the task just stops running and never runs (depends
on where the sched_rt b/w timer runs). With the patch, the
task is throttled and runs as expected.
[ bharata, suggestions on how to pick the rt_se belong to the
rt_rq and correct cpu ]
Signed-off-by: Balbir Singh <balbir@linux.vnet.ibm.com>
Acked-by: Bharata B Rao <bharata@linux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: stable@kernel.org
LKML-Reference: <20110303113435.GA2868@balbir.in.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2011-03-03 11:34:35 +00:00
|
|
|
} else if (rt_rq->rt_nr_running) {
|
2008-06-19 12:22:28 +00:00
|
|
|
idle = 0;
|
sched: Fix sched rt group scheduling when hierachy is enabled
The current sched rt code is broken when it comes to hierarchical
scheduling, this patch fixes two problems
1. It adds redundant enqueuing (harmless) when it finds a queue
has tasks enqueued, but it has no run time and it is not
throttled.
2. The most important change is in sched_rt_rq_enqueue/dequeue.
The code just picks the rt_rq belonging to the current cpu
on which the period timer runs, the patch fixes it, so that
the correct rt_se is enqueued/dequeued.
Tested with a simple hierarchy
/c/d, c and d assigned similar runtimes of 50,000 and a while
1 loop runs within "d". Both c and d get throttled, without
the patch, the task just stops running and never runs (depends
on where the sched_rt b/w timer runs). With the patch, the
task is throttled and runs as expected.
[ bharata, suggestions on how to pick the rt_se belong to the
rt_rq and correct cpu ]
Signed-off-by: Balbir Singh <balbir@linux.vnet.ibm.com>
Acked-by: Bharata B Rao <bharata@linux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: stable@kernel.org
LKML-Reference: <20110303113435.GA2868@balbir.in.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2011-03-03 11:34:35 +00:00
|
|
|
if (!rt_rq_throttled(rt_rq))
|
|
|
|
enqueue = 1;
|
|
|
|
}
|
2011-10-18 20:03:48 +00:00
|
|
|
if (rt_rq->rt_throttled)
|
|
|
|
throttled = 1;
|
2008-06-19 12:22:26 +00:00
|
|
|
|
|
|
|
if (enqueue)
|
|
|
|
sched_rt_rq_enqueue(rt_rq);
|
sched/core: Avoid obvious double update_rq_clock warning
When we use raw_spin_rq_lock() to acquire the rq lock and have to
update the rq clock while holding the lock, the kernel may issue
a WARN_DOUBLE_CLOCK warning.
Since we directly use raw_spin_rq_lock() to acquire rq lock instead of
rq_lock(), there is no corresponding change to rq->clock_update_flags.
In particular, we have obtained the rq lock of other CPUs, the
rq->clock_update_flags of this CPU may be RQCF_UPDATED at this time, and
then calling update_rq_clock() will trigger the WARN_DOUBLE_CLOCK warning.
So we need to clear RQCF_UPDATED of rq->clock_update_flags to avoid
the WARN_DOUBLE_CLOCK warning.
For the sched_rt_period_timer() and migrate_task_rq_dl() cases
we simply replace raw_spin_rq_lock()/raw_spin_rq_unlock() with
rq_lock()/rq_unlock().
For the {pull,push}_{rt,dl}_task() cases, we add the
double_rq_clock_clear_update() function to clear RQCF_UPDATED of
rq->clock_update_flags, and call double_rq_clock_clear_update()
before double_lock_balance()/double_rq_lock() returns to avoid the
WARN_DOUBLE_CLOCK warning.
Some call trace reports:
Call Trace 1:
<IRQ>
sched_rt_period_timer+0x10f/0x3a0
? enqueue_top_rt_rq+0x110/0x110
__hrtimer_run_queues+0x1a9/0x490
hrtimer_interrupt+0x10b/0x240
__sysvec_apic_timer_interrupt+0x8a/0x250
sysvec_apic_timer_interrupt+0x9a/0xd0
</IRQ>
<TASK>
asm_sysvec_apic_timer_interrupt+0x12/0x20
Call Trace 2:
<TASK>
activate_task+0x8b/0x110
push_rt_task.part.108+0x241/0x2c0
push_rt_tasks+0x15/0x30
finish_task_switch+0xaa/0x2e0
? __switch_to+0x134/0x420
__schedule+0x343/0x8e0
? hrtimer_start_range_ns+0x101/0x340
schedule+0x4e/0xb0
do_nanosleep+0x8e/0x160
hrtimer_nanosleep+0x89/0x120
? hrtimer_init_sleeper+0x90/0x90
__x64_sys_nanosleep+0x96/0xd0
do_syscall_64+0x34/0x90
entry_SYSCALL_64_after_hwframe+0x44/0xae
Call Trace 3:
<TASK>
deactivate_task+0x93/0xe0
pull_rt_task+0x33e/0x400
balance_rt+0x7e/0x90
__schedule+0x62f/0x8e0
do_task_dead+0x3f/0x50
do_exit+0x7b8/0xbb0
do_group_exit+0x2d/0x90
get_signal+0x9df/0x9e0
? preempt_count_add+0x56/0xa0
? __remove_hrtimer+0x35/0x70
arch_do_signal_or_restart+0x36/0x720
? nanosleep_copyout+0x39/0x50
? do_nanosleep+0x131/0x160
? audit_filter_inodes+0xf5/0x120
exit_to_user_mode_prepare+0x10f/0x1e0
syscall_exit_to_user_mode+0x17/0x30
do_syscall_64+0x40/0x90
entry_SYSCALL_64_after_hwframe+0x44/0xae
Call Trace 4:
update_rq_clock+0x128/0x1a0
migrate_task_rq_dl+0xec/0x310
set_task_cpu+0x84/0x1e4
try_to_wake_up+0x1d8/0x5c0
wake_up_process+0x1c/0x30
hrtimer_wakeup+0x24/0x3c
__hrtimer_run_queues+0x114/0x270
hrtimer_interrupt+0xe8/0x244
arch_timer_handler_phys+0x30/0x50
handle_percpu_devid_irq+0x88/0x140
generic_handle_domain_irq+0x40/0x60
gic_handle_irq+0x48/0xe0
call_on_irq_stack+0x2c/0x60
do_interrupt_handler+0x80/0x84
Steps to reproduce:
1. Enable CONFIG_SCHED_DEBUG when compiling the kernel
2. echo 1 > /sys/kernel/debug/clear_warn_once
echo "WARN_DOUBLE_CLOCK" > /sys/kernel/debug/sched/features
echo "NO_RT_PUSH_IPI" > /sys/kernel/debug/sched/features
3. Run some rt/dl tasks that periodically work and sleep, e.g.
Create 2*n rt or dl (90% running) tasks via rt-app (on a system
with n CPUs), and Dietmar Eggemann reports Call Trace 4 when running
on PREEMPT_RT kernel.
Signed-off-by: Hao Jia <jiahao.os@bytedance.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Link: https://lore.kernel.org/r/20220430085843.62939-2-jiahao.os@bytedance.com
2022-04-30 08:58:42 +00:00
|
|
|
rq_unlock(rq, &rf);
|
2008-06-19 12:22:26 +00:00
|
|
|
}
|
|
|
|
|
2011-10-18 20:03:48 +00:00
|
|
|
if (!throttled && (!rt_bandwidth_enabled() || rt_b->rt_runtime == RUNTIME_INF))
|
|
|
|
return 1;
|
|
|
|
|
2008-06-19 12:22:26 +00:00
|
|
|
return idle;
|
|
|
|
}
|
2008-04-19 17:44:58 +00:00
|
|
|
|
2008-01-25 20:08:30 +00:00
|
|
|
static inline int rt_se_prio(struct sched_rt_entity *rt_se)
|
|
|
|
{
|
2008-02-13 14:45:40 +00:00
|
|
|
#ifdef CONFIG_RT_GROUP_SCHED
|
2008-01-25 20:08:30 +00:00
|
|
|
struct rt_rq *rt_rq = group_rt_rq(rt_se);
|
|
|
|
|
|
|
|
if (rt_rq)
|
2008-12-29 14:39:49 +00:00
|
|
|
return rt_rq->highest_prio.curr;
|
2008-01-25 20:08:30 +00:00
|
|
|
#endif
|
|
|
|
|
|
|
|
return rt_task_of(rt_se)->prio;
|
|
|
|
}
|
|
|
|
|
2008-02-13 14:45:39 +00:00
|
|
|
static int sched_rt_runtime_exceeded(struct rt_rq *rt_rq)
|
2008-01-25 20:08:30 +00:00
|
|
|
{
|
2008-02-13 14:45:39 +00:00
|
|
|
u64 runtime = sched_rt_runtime(rt_rq);
|
2008-01-25 20:08:29 +00:00
|
|
|
|
|
|
|
if (rt_rq->rt_throttled)
|
2008-02-13 14:45:39 +00:00
|
|
|
return rt_rq_throttled(rt_rq);
|
2008-01-25 20:08:29 +00:00
|
|
|
|
2011-11-29 03:03:56 +00:00
|
|
|
if (runtime >= sched_rt_period(rt_rq))
|
2008-04-19 17:44:58 +00:00
|
|
|
return 0;
|
|
|
|
|
2008-06-19 12:22:25 +00:00
|
|
|
balance_runtime(rt_rq);
|
|
|
|
runtime = sched_rt_runtime(rt_rq);
|
|
|
|
if (runtime == RUNTIME_INF)
|
|
|
|
return 0;
|
2008-04-19 17:44:58 +00:00
|
|
|
|
2008-02-13 14:45:39 +00:00
|
|
|
if (rt_rq->rt_time > runtime) {
|
2011-10-18 20:03:48 +00:00
|
|
|
struct rt_bandwidth *rt_b = sched_rt_bandwidth(rt_rq);
|
|
|
|
|
|
|
|
/*
|
|
|
|
* Don't actually throttle groups that have no runtime assigned
|
|
|
|
* but accrue some time due to boosting.
|
|
|
|
*/
|
|
|
|
if (likely(rt_b->rt_runtime)) {
|
|
|
|
rt_rq->rt_throttled = 1;
|
2014-06-04 23:11:41 +00:00
|
|
|
printk_deferred_once("sched: RT throttling activated\n");
|
2011-10-18 20:03:48 +00:00
|
|
|
} else {
|
|
|
|
/*
|
|
|
|
* In case we did anyway, make it go away,
|
|
|
|
* replenishment is a joke, since it will replenish us
|
|
|
|
* with exactly 0 ns.
|
|
|
|
*/
|
|
|
|
rt_rq->rt_time = 0;
|
|
|
|
}
|
|
|
|
|
2008-02-13 14:45:39 +00:00
|
|
|
if (rt_rq_throttled(rt_rq)) {
|
2008-02-13 14:45:39 +00:00
|
|
|
sched_rt_rq_dequeue(rt_rq);
|
2008-02-13 14:45:39 +00:00
|
|
|
return 1;
|
|
|
|
}
|
2008-01-25 20:08:29 +00:00
|
|
|
}
|
|
|
|
|
|
|
|
return 0;
|
|
|
|
}
|
|
|
|
|
2007-07-09 16:51:58 +00:00
|
|
|
/*
|
|
|
|
* Update the current task's runtime statistics. Skip current tasks that
|
|
|
|
* are not in our scheduling class.
|
|
|
|
*/
|
2007-10-15 15:00:13 +00:00
|
|
|
static void update_curr_rt(struct rq *rq)
|
2007-07-09 16:51:58 +00:00
|
|
|
{
|
|
|
|
struct task_struct *curr = rq->curr;
|
2008-01-25 20:08:30 +00:00
|
|
|
struct sched_rt_entity *rt_se = &curr->rt;
|
2007-07-09 16:51:58 +00:00
|
|
|
u64 delta_exec;
|
2018-02-06 01:53:28 +00:00
|
|
|
u64 now;
|
2007-07-09 16:51:58 +00:00
|
|
|
|
2011-02-02 12:19:48 +00:00
|
|
|
if (curr->sched_class != &rt_sched_class)
|
2007-07-09 16:51:58 +00:00
|
|
|
return;
|
|
|
|
|
2018-02-06 01:53:28 +00:00
|
|
|
now = rq_clock_task(rq);
|
2018-02-05 03:18:41 +00:00
|
|
|
delta_exec = now - curr->se.exec_start;
|
2013-01-30 12:50:36 +00:00
|
|
|
if (unlikely((s64)delta_exec <= 0))
|
|
|
|
return;
|
2007-08-02 15:41:40 +00:00
|
|
|
|
sched: Make struct sched_statistics independent of fair sched class
If we want to use the schedstats facility to trace other sched classes, we
should make it independent of fair sched class. The struct sched_statistics
is the schedular statistics of a task_struct or a task_group. So we can
move it into struct task_struct and struct task_group to achieve the goal.
After the patch, schestats are orgnized as follows,
struct task_struct {
...
struct sched_entity se;
struct sched_rt_entity rt;
struct sched_dl_entity dl;
...
struct sched_statistics stats;
...
};
Regarding the task group, schedstats is only supported for fair group
sched, and a new struct sched_entity_stats is introduced, suggested by
Peter -
struct sched_entity_stats {
struct sched_entity se;
struct sched_statistics stats;
} __no_randomize_layout;
Then with the se in a task_group, we can easily get the stats.
The sched_statistics members may be frequently modified when schedstats is
enabled, in order to avoid impacting on random data which may in the same
cacheline with them, the struct sched_statistics is defined as cacheline
aligned.
As this patch changes the core struct of scheduler, so I verified the
performance it may impact on the scheduler with 'perf bench sched
pipe', suggested by Mel. Below is the result, in which all the values
are in usecs/op.
Before After
kernel.sched_schedstats=0 5.2~5.4 5.2~5.4
kernel.sched_schedstats=1 5.3~5.5 5.3~5.5
[These data is a little difference with the earlier version, that is
because my old test machine is destroyed so I have to use a new
different test machine.]
Almost no impact on the sched performance.
No functional change.
[lkp@intel.com: reported build failure in earlier version]
Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Mel Gorman <mgorman@suse.de>
Link: https://lore.kernel.org/r/20210905143547.4668-3-laoar.shao@gmail.com
2021-09-05 14:35:41 +00:00
|
|
|
schedstat_set(curr->stats.exec_max,
|
|
|
|
max(curr->stats.exec_max, delta_exec));
|
2007-07-09 16:51:58 +00:00
|
|
|
|
2021-09-05 14:35:44 +00:00
|
|
|
trace_sched_stat_runtime(curr, delta_exec, 0);
|
|
|
|
|
2022-08-24 08:28:56 +00:00
|
|
|
update_current_exec_runtime(curr, now, delta_exec);
|
2008-01-25 20:08:29 +00:00
|
|
|
|
2008-08-19 10:33:04 +00:00
|
|
|
if (!rt_bandwidth_enabled())
|
|
|
|
return;
|
|
|
|
|
2008-04-19 17:44:59 +00:00
|
|
|
for_each_sched_rt_entity(rt_se) {
|
2014-05-25 14:23:31 +00:00
|
|
|
struct rt_rq *rt_rq = rt_rq_of_se(rt_se);
|
2021-12-03 03:36:18 +00:00
|
|
|
int exceeded;
|
2008-04-19 17:44:59 +00:00
|
|
|
|
2008-08-19 10:33:03 +00:00
|
|
|
if (sched_rt_runtime(rt_rq) != RUNTIME_INF) {
|
2009-11-17 14:32:06 +00:00
|
|
|
raw_spin_lock(&rt_rq->rt_runtime_lock);
|
2008-08-19 10:33:03 +00:00
|
|
|
rt_rq->rt_time += delta_exec;
|
2021-12-03 03:36:18 +00:00
|
|
|
exceeded = sched_rt_runtime_exceeded(rt_rq);
|
|
|
|
if (exceeded)
|
2014-06-28 20:03:57 +00:00
|
|
|
resched_curr(rq);
|
2009-11-17 14:32:06 +00:00
|
|
|
raw_spin_unlock(&rt_rq->rt_runtime_lock);
|
2021-12-03 03:36:18 +00:00
|
|
|
if (exceeded)
|
|
|
|
do_start_rt_bandwidth(sched_rt_bandwidth(rt_rq));
|
2008-08-19 10:33:03 +00:00
|
|
|
}
|
2008-04-19 17:44:59 +00:00
|
|
|
}
|
2007-07-09 16:51:58 +00:00
|
|
|
}
|
|
|
|
|
2014-03-14 22:15:00 +00:00
|
|
|
static void
|
2022-06-28 09:22:59 +00:00
|
|
|
dequeue_top_rt_rq(struct rt_rq *rt_rq, unsigned int count)
|
2014-03-14 22:15:00 +00:00
|
|
|
{
|
|
|
|
struct rq *rq = rq_of_rt_rq(rt_rq);
|
|
|
|
|
|
|
|
BUG_ON(&rq->rt != rt_rq);
|
|
|
|
|
|
|
|
if (!rt_rq->rt_queued)
|
|
|
|
return;
|
|
|
|
|
|
|
|
BUG_ON(!rq->nr_running);
|
|
|
|
|
2022-06-28 09:22:59 +00:00
|
|
|
sub_nr_running(rq, count);
|
2014-03-14 22:15:00 +00:00
|
|
|
rt_rq->rt_queued = 0;
|
2017-12-20 15:26:12 +00:00
|
|
|
|
2014-03-14 22:15:00 +00:00
|
|
|
}
|
|
|
|
|
|
|
|
static void
|
|
|
|
enqueue_top_rt_rq(struct rt_rq *rt_rq)
|
|
|
|
{
|
|
|
|
struct rq *rq = rq_of_rt_rq(rt_rq);
|
|
|
|
|
|
|
|
BUG_ON(&rq->rt != rt_rq);
|
|
|
|
|
|
|
|
if (rt_rq->rt_queued)
|
|
|
|
return;
|
2018-06-26 13:53:22 +00:00
|
|
|
|
|
|
|
if (rt_rq_throttled(rt_rq))
|
2014-03-14 22:15:00 +00:00
|
|
|
return;
|
|
|
|
|
2018-06-26 13:53:22 +00:00
|
|
|
if (rt_rq->rt_nr_running) {
|
|
|
|
add_nr_running(rq, rt_rq->rt_nr_running);
|
|
|
|
rt_rq->rt_queued = 1;
|
|
|
|
}
|
2017-12-20 15:26:12 +00:00
|
|
|
|
|
|
|
/* Kick cpufreq (see the comment in kernel/sched/sched.h). */
|
|
|
|
cpufreq_update_util(rq, 0);
|
2014-03-14 22:15:00 +00:00
|
|
|
}
|
|
|
|
|
2009-01-14 14:10:04 +00:00
|
|
|
#if defined CONFIG_SMP
|
2008-12-29 14:39:49 +00:00
|
|
|
|
2009-01-14 14:10:04 +00:00
|
|
|
static void
|
|
|
|
inc_rt_prio_smp(struct rt_rq *rt_rq, int prio, int prev_prio)
|
2008-01-25 20:08:03 +00:00
|
|
|
{
|
2008-12-29 14:39:49 +00:00
|
|
|
struct rq *rq = rq_of_rt_rq(rt_rq);
|
2008-06-04 19:04:05 +00:00
|
|
|
|
2013-11-27 15:59:13 +00:00
|
|
|
#ifdef CONFIG_RT_GROUP_SCHED
|
|
|
|
/*
|
|
|
|
* Change rq's cpupri only if rt_rq is the top queue.
|
|
|
|
*/
|
|
|
|
if (&rq->rt != rt_rq)
|
|
|
|
return;
|
|
|
|
#endif
|
sched: Use pushable_tasks to determine next highest prio
Hillf Danton proposed a patch (see link) that cleaned up the
sched_rt code that calculates the priority of the next highest priority
task to be used in finding run queues to pull from.
His patch removed the calculating of the next prio to just use the current
prio when deteriming if we should examine a run queue to pull from. The problem
with his patch was that it caused more false checks. Because we check a run
queue for pushable tasks if the current priority of that run queue is higher
in priority than the task about to run on our run queue. But after grabbing
the locks and doing the real check, we find that there may not be a task
that has a higher prio task to pull. Thus the locks were taken with nothing to
do.
I added some trace_printks() to record when and how many times the run queue
locks were taken to check for pullable tasks, compared to how many times we
pulled a task.
With the current method, it was:
3806 locks taken vs 2812 pulled tasks
With Hillf's patch:
6728 locks taken vs 2804 pulled tasks
The number of times locks were taken to pull a task went up almost double with
no more success rate.
But his patch did get me thinking. When we look at the priority of the highest
task to consider taking the locks to do a pull, a failure to pull can be one
of the following: (in order of most likely)
o RT task was pushed off already between the check and taking the lock
o Waiting RT task can not be migrated
o RT task's CPU affinity does not include the target run queue's CPU
o RT task's priority changed between the check and taking the lock
And with Hillf's patch, the thing that caused most of the failures, is
the RT task to pull was not at the right priority to pull (not greater than
the current RT task priority on the target run queue).
Most of the above cases we can't help. But the current method does not check
if the next highest prio RT task can be migrated or not, and if it can not,
we still grab the locks to do the test (we don't find out about this fact until
after we have the locks). I thought about this case, and realized that the
pushable task plist that is maintained only holds RT tasks that can migrate.
If we move the calculating of the next highest prio task from the inc/dec_rt_task()
functions into the queuing of the pushable tasks, then we only measure the
priorities of those tasks that we push, and we get this basically for free.
Not only does this patch make the code a little more efficient, it cleans it
up and makes it a little simpler.
Thanks to Hillf Danton for inspiring me on this patch.
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Hillf Danton <dhillf@gmail.com>
Cc: Gregory Haskins <ghaskins@novell.com>
Link: http://lkml.kernel.org/r/BANLkTimQ67180HxCx5vgMqumqw1EkFh3qg@mail.gmail.com
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2011-06-17 01:55:23 +00:00
|
|
|
if (rq->online && prio < prev_prio)
|
|
|
|
cpupri_set(&rq->rd->cpupri, rq->cpu, prio);
|
2009-01-14 14:10:04 +00:00
|
|
|
}
|
2008-01-25 20:08:07 +00:00
|
|
|
|
2009-01-14 14:10:04 +00:00
|
|
|
static void
|
|
|
|
dec_rt_prio_smp(struct rt_rq *rt_rq, int prio, int prev_prio)
|
|
|
|
{
|
|
|
|
struct rq *rq = rq_of_rt_rq(rt_rq);
|
2008-04-19 17:44:57 +00:00
|
|
|
|
2013-11-27 15:59:13 +00:00
|
|
|
#ifdef CONFIG_RT_GROUP_SCHED
|
|
|
|
/*
|
|
|
|
* Change rq's cpupri only if rt_rq is the top queue.
|
|
|
|
*/
|
|
|
|
if (&rq->rt != rt_rq)
|
|
|
|
return;
|
|
|
|
#endif
|
2009-01-14 14:10:04 +00:00
|
|
|
if (rq->online && rt_rq->highest_prio.curr != prev_prio)
|
|
|
|
cpupri_set(&rq->rd->cpupri, rq->cpu, rt_rq->highest_prio.curr);
|
2008-01-25 20:08:03 +00:00
|
|
|
}
|
|
|
|
|
2009-01-14 14:10:04 +00:00
|
|
|
#else /* CONFIG_SMP */
|
|
|
|
|
2008-01-25 20:08:30 +00:00
|
|
|
static inline
|
2009-01-14 14:10:04 +00:00
|
|
|
void inc_rt_prio_smp(struct rt_rq *rt_rq, int prio, int prev_prio) {}
|
|
|
|
static inline
|
|
|
|
void dec_rt_prio_smp(struct rt_rq *rt_rq, int prio, int prev_prio) {}
|
|
|
|
|
|
|
|
#endif /* CONFIG_SMP */
|
2008-05-12 19:21:01 +00:00
|
|
|
|
2008-02-13 14:45:40 +00:00
|
|
|
#if defined CONFIG_SMP || defined CONFIG_RT_GROUP_SCHED
|
2009-01-14 14:10:04 +00:00
|
|
|
static void
|
|
|
|
inc_rt_prio(struct rt_rq *rt_rq, int prio)
|
|
|
|
{
|
|
|
|
int prev_prio = rt_rq->highest_prio.curr;
|
|
|
|
|
|
|
|
if (prio < prev_prio)
|
|
|
|
rt_rq->highest_prio.curr = prio;
|
|
|
|
|
|
|
|
inc_rt_prio_smp(rt_rq, prio, prev_prio);
|
|
|
|
}
|
|
|
|
|
|
|
|
static void
|
|
|
|
dec_rt_prio(struct rt_rq *rt_rq, int prio)
|
|
|
|
{
|
|
|
|
int prev_prio = rt_rq->highest_prio.curr;
|
|
|
|
|
2008-01-25 20:08:30 +00:00
|
|
|
if (rt_rq->rt_nr_running) {
|
2008-01-25 20:08:04 +00:00
|
|
|
|
2009-01-14 14:10:04 +00:00
|
|
|
WARN_ON(prio < prev_prio);
|
2008-01-25 20:08:04 +00:00
|
|
|
|
2008-12-29 14:39:49 +00:00
|
|
|
/*
|
2009-01-14 14:10:04 +00:00
|
|
|
* This may have been our highest task, and therefore
|
|
|
|
* we may have some recomputation to do
|
2008-12-29 14:39:49 +00:00
|
|
|
*/
|
2009-01-14 14:10:04 +00:00
|
|
|
if (prio == prev_prio) {
|
2008-12-29 14:39:49 +00:00
|
|
|
struct rt_prio_array *array = &rt_rq->active;
|
|
|
|
|
|
|
|
rt_rq->highest_prio.curr =
|
2008-01-25 20:08:04 +00:00
|
|
|
sched_find_first_bit(array->bitmap);
|
2008-12-29 14:39:49 +00:00
|
|
|
}
|
|
|
|
|
2020-10-14 19:06:49 +00:00
|
|
|
} else {
|
|
|
|
rt_rq->highest_prio.curr = MAX_RT_PRIO-1;
|
|
|
|
}
|
2008-01-25 20:08:07 +00:00
|
|
|
|
2009-01-14 14:10:04 +00:00
|
|
|
dec_rt_prio_smp(rt_rq, prio, prev_prio);
|
|
|
|
}
|
2008-06-04 19:04:05 +00:00
|
|
|
|
2009-01-14 14:10:04 +00:00
|
|
|
#else
|
|
|
|
|
|
|
|
static inline void inc_rt_prio(struct rt_rq *rt_rq, int prio) {}
|
|
|
|
static inline void dec_rt_prio(struct rt_rq *rt_rq, int prio) {}
|
|
|
|
|
|
|
|
#endif /* CONFIG_SMP || CONFIG_RT_GROUP_SCHED */
|
2008-05-12 19:21:01 +00:00
|
|
|
|
2008-02-13 14:45:40 +00:00
|
|
|
#ifdef CONFIG_RT_GROUP_SCHED
|
2009-01-14 14:10:04 +00:00
|
|
|
|
|
|
|
static void
|
|
|
|
inc_rt_group(struct sched_rt_entity *rt_se, struct rt_rq *rt_rq)
|
|
|
|
{
|
|
|
|
if (rt_se_boosted(rt_se))
|
|
|
|
rt_rq->rt_nr_boosted++;
|
|
|
|
|
|
|
|
if (rt_rq->tg)
|
|
|
|
start_rt_bandwidth(&rt_rq->tg->rt_bandwidth);
|
|
|
|
}
|
|
|
|
|
|
|
|
static void
|
|
|
|
dec_rt_group(struct sched_rt_entity *rt_se, struct rt_rq *rt_rq)
|
|
|
|
{
|
2008-02-13 14:45:39 +00:00
|
|
|
if (rt_se_boosted(rt_se))
|
|
|
|
rt_rq->rt_nr_boosted--;
|
|
|
|
|
|
|
|
WARN_ON(!rt_rq->rt_nr_running && rt_rq->rt_nr_boosted);
|
2009-01-14 14:10:04 +00:00
|
|
|
}
|
|
|
|
|
|
|
|
#else /* CONFIG_RT_GROUP_SCHED */
|
|
|
|
|
|
|
|
static void
|
|
|
|
inc_rt_group(struct sched_rt_entity *rt_se, struct rt_rq *rt_rq)
|
|
|
|
{
|
|
|
|
start_rt_bandwidth(&def_rt_bandwidth);
|
|
|
|
}
|
|
|
|
|
|
|
|
static inline
|
|
|
|
void dec_rt_group(struct sched_rt_entity *rt_se, struct rt_rq *rt_rq) {}
|
|
|
|
|
|
|
|
#endif /* CONFIG_RT_GROUP_SCHED */
|
|
|
|
|
2014-03-14 22:14:49 +00:00
|
|
|
static inline
|
|
|
|
unsigned int rt_se_nr_running(struct sched_rt_entity *rt_se)
|
|
|
|
{
|
|
|
|
struct rt_rq *group_rq = group_rt_rq(rt_se);
|
|
|
|
|
|
|
|
if (group_rq)
|
|
|
|
return group_rq->rt_nr_running;
|
|
|
|
else
|
|
|
|
return 1;
|
|
|
|
}
|
|
|
|
|
2015-11-04 17:17:10 +00:00
|
|
|
static inline
|
|
|
|
unsigned int rt_se_rr_nr_running(struct sched_rt_entity *rt_se)
|
|
|
|
{
|
|
|
|
struct rt_rq *group_rq = group_rt_rq(rt_se);
|
|
|
|
struct task_struct *tsk;
|
|
|
|
|
|
|
|
if (group_rq)
|
|
|
|
return group_rq->rr_nr_running;
|
|
|
|
|
|
|
|
tsk = rt_task_of(rt_se);
|
|
|
|
|
|
|
|
return (tsk->policy == SCHED_RR) ? 1 : 0;
|
|
|
|
}
|
|
|
|
|
2009-01-14 14:10:04 +00:00
|
|
|
static inline
|
|
|
|
void inc_rt_tasks(struct sched_rt_entity *rt_se, struct rt_rq *rt_rq)
|
|
|
|
{
|
|
|
|
int prio = rt_se_prio(rt_se);
|
|
|
|
|
|
|
|
WARN_ON(!rt_prio(prio));
|
2014-03-14 22:14:49 +00:00
|
|
|
rt_rq->rt_nr_running += rt_se_nr_running(rt_se);
|
2015-11-04 17:17:10 +00:00
|
|
|
rt_rq->rr_nr_running += rt_se_rr_nr_running(rt_se);
|
2009-01-14 14:10:04 +00:00
|
|
|
|
|
|
|
inc_rt_prio(rt_rq, prio);
|
|
|
|
inc_rt_migration(rt_se, rt_rq);
|
|
|
|
inc_rt_group(rt_se, rt_rq);
|
|
|
|
}
|
|
|
|
|
|
|
|
static inline
|
|
|
|
void dec_rt_tasks(struct sched_rt_entity *rt_se, struct rt_rq *rt_rq)
|
|
|
|
{
|
|
|
|
WARN_ON(!rt_prio(rt_se_prio(rt_se)));
|
|
|
|
WARN_ON(!rt_rq->rt_nr_running);
|
2014-03-14 22:14:49 +00:00
|
|
|
rt_rq->rt_nr_running -= rt_se_nr_running(rt_se);
|
2015-11-04 17:17:10 +00:00
|
|
|
rt_rq->rr_nr_running -= rt_se_rr_nr_running(rt_se);
|
2009-01-14 14:10:04 +00:00
|
|
|
|
|
|
|
dec_rt_prio(rt_rq, rt_se_prio(rt_se));
|
|
|
|
dec_rt_migration(rt_se, rt_rq);
|
|
|
|
dec_rt_group(rt_se, rt_rq);
|
2008-01-25 20:08:03 +00:00
|
|
|
}
|
|
|
|
|
2016-01-18 14:27:07 +00:00
|
|
|
/*
|
|
|
|
* Change rt_se->run_list location unless SAVE && !MOVE
|
|
|
|
*
|
|
|
|
* assumes ENQUEUE/DEQUEUE flags match
|
|
|
|
*/
|
|
|
|
static inline bool move_entity(unsigned int flags)
|
|
|
|
{
|
|
|
|
if ((flags & (DEQUEUE_SAVE | DEQUEUE_MOVE)) == DEQUEUE_SAVE)
|
|
|
|
return false;
|
|
|
|
|
|
|
|
return true;
|
|
|
|
}
|
|
|
|
|
|
|
|
static void __delist_rt_entity(struct sched_rt_entity *rt_se, struct rt_prio_array *array)
|
|
|
|
{
|
|
|
|
list_del_init(&rt_se->run_list);
|
|
|
|
|
|
|
|
if (list_empty(array->queue + rt_se_prio(rt_se)))
|
|
|
|
__clear_bit(rt_se_prio(rt_se), array->bitmap);
|
|
|
|
|
|
|
|
rt_se->on_list = 0;
|
|
|
|
}
|
|
|
|
|
sched/rt: Support schedstats for RT sched class
We want to measure the latency of RT tasks in our production
environment with schedstats facility, but currently schedstats is only
supported for fair sched class. This patch enable it for RT sched class
as well.
After we make the struct sched_statistics and the helpers of it
independent of fair sched class, we can easily use the schedstats
facility for RT sched class.
The schedstat usage in RT sched class is similar with fair sched class,
for example,
fair RT
enqueue update_stats_enqueue_fair update_stats_enqueue_rt
dequeue update_stats_dequeue_fair update_stats_dequeue_rt
put_prev_task update_stats_wait_start update_stats_wait_start_rt
set_next_task update_stats_wait_end update_stats_wait_end_rt
The user can get the schedstats information in the same way in fair sched
class. For example,
fair RT
/proc/[pid]/sched /proc/[pid]/sched
schedstats is not supported for RT group.
The output of a RT task's schedstats as follows,
$ cat /proc/10349/sched
...
sum_sleep_runtime : 972.434535
sum_block_runtime : 960.433522
wait_start : 188510.871584
sleep_start : 0.000000
block_start : 0.000000
sleep_max : 12.001013
block_max : 952.660622
exec_max : 0.049629
slice_max : 0.000000
wait_max : 0.018538
wait_sum : 0.424340
wait_count : 49
iowait_sum : 956.495640
iowait_count : 24
nr_migrations_cold : 0
nr_failed_migrations_affine : 0
nr_failed_migrations_running : 0
nr_failed_migrations_hot : 0
nr_forced_migrations : 0
nr_wakeups : 49
nr_wakeups_sync : 0
nr_wakeups_migrate : 0
nr_wakeups_local : 49
nr_wakeups_remote : 0
nr_wakeups_affine : 0
nr_wakeups_affine_attempts : 0
nr_wakeups_passive : 0
nr_wakeups_idle : 0
...
The sched:sched_stat_{wait, sleep, iowait, blocked} tracepoints can
be used to trace RT tasks as well. The output of these tracepoints for a
RT tasks as follows,
- runtime
stress-10352 [004] d.h. 1035.382286: sched_stat_runtime: comm=stress pid=10352 runtime=995769 [ns] vruntime=0 [ns]
[vruntime=0 means it is a RT task]
- wait
<idle>-0 [004] dN.. 1227.688544: sched_stat_wait: comm=stress pid=10352 delay=46849882 [ns]
- blocked
kworker/4:1-465 [004] dN.. 1585.676371: sched_stat_blocked: comm=stress pid=17194 delay=189963 [ns]
- iowait
kworker/4:1-465 [004] dN.. 1585.675330: sched_stat_iowait: comm=stress pid=17189 delay=182848 [ns]
- sleep
sleep-18194 [023] dN.. 1780.891840: sched_stat_sleep: comm=sleep.sh pid=17767 delay=1001160770 [ns]
sleep-18196 [023] dN.. 1781.893208: sched_stat_sleep: comm=sleep.sh pid=17767 delay=1001161970 [ns]
sleep-18197 [023] dN.. 1782.894544: sched_stat_sleep: comm=sleep.sh pid=17767 delay=1001128840 [ns]
[ In sleep.sh, it sleeps 1 sec each time. ]
[lkp@intel.com: reported build failure in earlier version]
Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20210905143547.4668-7-laoar.shao@gmail.com
2021-09-05 14:35:45 +00:00
|
|
|
static inline struct sched_statistics *
|
|
|
|
__schedstats_from_rt_se(struct sched_rt_entity *rt_se)
|
|
|
|
{
|
|
|
|
#ifdef CONFIG_RT_GROUP_SCHED
|
|
|
|
/* schedstats is not supported for rt group. */
|
|
|
|
if (!rt_entity_is_task(rt_se))
|
|
|
|
return NULL;
|
|
|
|
#endif
|
|
|
|
|
|
|
|
return &rt_task_of(rt_se)->stats;
|
|
|
|
}
|
|
|
|
|
|
|
|
static inline void
|
|
|
|
update_stats_wait_start_rt(struct rt_rq *rt_rq, struct sched_rt_entity *rt_se)
|
|
|
|
{
|
|
|
|
struct sched_statistics *stats;
|
|
|
|
struct task_struct *p = NULL;
|
|
|
|
|
|
|
|
if (!schedstat_enabled())
|
|
|
|
return;
|
|
|
|
|
|
|
|
if (rt_entity_is_task(rt_se))
|
|
|
|
p = rt_task_of(rt_se);
|
|
|
|
|
|
|
|
stats = __schedstats_from_rt_se(rt_se);
|
|
|
|
if (!stats)
|
|
|
|
return;
|
|
|
|
|
|
|
|
__update_stats_wait_start(rq_of_rt_rq(rt_rq), p, stats);
|
|
|
|
}
|
|
|
|
|
|
|
|
static inline void
|
|
|
|
update_stats_enqueue_sleeper_rt(struct rt_rq *rt_rq, struct sched_rt_entity *rt_se)
|
|
|
|
{
|
|
|
|
struct sched_statistics *stats;
|
|
|
|
struct task_struct *p = NULL;
|
|
|
|
|
|
|
|
if (!schedstat_enabled())
|
|
|
|
return;
|
|
|
|
|
|
|
|
if (rt_entity_is_task(rt_se))
|
|
|
|
p = rt_task_of(rt_se);
|
|
|
|
|
|
|
|
stats = __schedstats_from_rt_se(rt_se);
|
|
|
|
if (!stats)
|
|
|
|
return;
|
|
|
|
|
|
|
|
__update_stats_enqueue_sleeper(rq_of_rt_rq(rt_rq), p, stats);
|
|
|
|
}
|
|
|
|
|
|
|
|
static inline void
|
|
|
|
update_stats_enqueue_rt(struct rt_rq *rt_rq, struct sched_rt_entity *rt_se,
|
|
|
|
int flags)
|
|
|
|
{
|
|
|
|
if (!schedstat_enabled())
|
|
|
|
return;
|
|
|
|
|
|
|
|
if (flags & ENQUEUE_WAKEUP)
|
|
|
|
update_stats_enqueue_sleeper_rt(rt_rq, rt_se);
|
|
|
|
}
|
|
|
|
|
|
|
|
static inline void
|
|
|
|
update_stats_wait_end_rt(struct rt_rq *rt_rq, struct sched_rt_entity *rt_se)
|
|
|
|
{
|
|
|
|
struct sched_statistics *stats;
|
|
|
|
struct task_struct *p = NULL;
|
|
|
|
|
|
|
|
if (!schedstat_enabled())
|
|
|
|
return;
|
|
|
|
|
|
|
|
if (rt_entity_is_task(rt_se))
|
|
|
|
p = rt_task_of(rt_se);
|
|
|
|
|
|
|
|
stats = __schedstats_from_rt_se(rt_se);
|
|
|
|
if (!stats)
|
|
|
|
return;
|
|
|
|
|
|
|
|
__update_stats_wait_end(rq_of_rt_rq(rt_rq), p, stats);
|
|
|
|
}
|
|
|
|
|
|
|
|
static inline void
|
|
|
|
update_stats_dequeue_rt(struct rt_rq *rt_rq, struct sched_rt_entity *rt_se,
|
|
|
|
int flags)
|
|
|
|
{
|
|
|
|
struct task_struct *p = NULL;
|
|
|
|
|
|
|
|
if (!schedstat_enabled())
|
|
|
|
return;
|
|
|
|
|
|
|
|
if (rt_entity_is_task(rt_se))
|
|
|
|
p = rt_task_of(rt_se);
|
|
|
|
|
|
|
|
if ((flags & DEQUEUE_SLEEP) && p) {
|
|
|
|
unsigned int state;
|
|
|
|
|
|
|
|
state = READ_ONCE(p->__state);
|
|
|
|
if (state & TASK_INTERRUPTIBLE)
|
|
|
|
__schedstat_set(p->stats.sleep_start,
|
|
|
|
rq_clock(rq_of_rt_rq(rt_rq)));
|
|
|
|
|
|
|
|
if (state & TASK_UNINTERRUPTIBLE)
|
|
|
|
__schedstat_set(p->stats.block_start,
|
|
|
|
rq_clock(rq_of_rt_rq(rt_rq)));
|
|
|
|
}
|
|
|
|
}
|
|
|
|
|
2016-01-18 14:27:07 +00:00
|
|
|
static void __enqueue_rt_entity(struct sched_rt_entity *rt_se, unsigned int flags)
|
2007-07-09 16:51:58 +00:00
|
|
|
{
|
2008-01-25 20:08:30 +00:00
|
|
|
struct rt_rq *rt_rq = rt_rq_of_se(rt_se);
|
|
|
|
struct rt_prio_array *array = &rt_rq->active;
|
|
|
|
struct rt_rq *group_rq = group_rt_rq(rt_se);
|
sched: rework of "prioritize non-migratable tasks over migratable ones"
regarding this commit: 45c01e824991b2dd0a332e19efc4901acb31209f
I think we can do it simpler. Please take a look at the patch below.
Instead of having 2 separate arrays (which is + ~800 bytes on x86_32 and
twice so on x86_64), let's add "exclusive" (the ones that are bound to
this CPU) tasks to the head of the queue and "shared" ones -- to the
end.
In case of a few newly woken up "exclusive" tasks, they are 'stacked'
(not queued as now), meaning that a task {i+1} is being placed in front
of the previously woken up task {i}. But I don't think that this
behavior may cause any realistic problems.
There are a couple of changes on top of this one.
(1) in check_preempt_curr_rt()
I don't think there is a need for the "pick_next_rt_entity(rq, &rq->rt)
!= &rq->curr->rt" check.
enqueue_task_rt(p) and check_preempt_curr_rt() are always called one
after another with rq->lock being held so the following check
"p->rt.nr_cpus_allowed == 1 && rq->curr->rt.nr_cpus_allowed != 1" should
be enough (well, just its left part) to guarantee that 'p' has been
queued in front of the 'curr'.
(2) in set_cpus_allowed_rt()
I don't thinks there is a need for requeue_task_rt() here.
Perhaps, the only case when 'requeue' (+ reschedule) might be useful is
as follows:
i) weight == 1 && cpu_isset(task_cpu(p), *new_mask)
i.e. a task is being bound to this CPU);
ii) 'p' != rq->curr
but here, 'p' has already been on this CPU for a while and was not
migrated. i.e. it's possible that 'rq->curr' would not have high chances
to be migrated right at this particular moment (although, has chance in
a bit longer term), should we allow it to be preempted.
Anyway, I think we should not perhaps make it more complex trying to
address some rare corner cases. For instance, that's why a single queue
approach would be preferable. Unless I'm missing something obvious, this
approach gives us similar functionality at lower cost.
Verified only compilation-wise.
(Almost)-Signed-off-by: Dmitry Adamushko <dmitry.adamushko@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-06-10 22:58:30 +00:00
|
|
|
struct list_head *queue = array->queue + rt_se_prio(rt_se);
|
2007-07-09 16:51:58 +00:00
|
|
|
|
2008-06-19 07:06:57 +00:00
|
|
|
/*
|
|
|
|
* Don't enqueue the group if its throttled, or when empty.
|
|
|
|
* The latter is a consequence of the former when a child group
|
|
|
|
* get throttled and the current group doesn't have any other
|
|
|
|
* active members.
|
|
|
|
*/
|
2016-01-18 14:27:07 +00:00
|
|
|
if (group_rq && (rt_rq_throttled(group_rq) || !group_rq->rt_nr_running)) {
|
|
|
|
if (rt_se->on_list)
|
|
|
|
__delist_rt_entity(rt_se, array);
|
2008-01-25 20:08:30 +00:00
|
|
|
return;
|
2016-01-18 14:27:07 +00:00
|
|
|
}
|
2008-01-25 20:08:03 +00:00
|
|
|
|
2016-01-18 14:27:07 +00:00
|
|
|
if (move_entity(flags)) {
|
|
|
|
WARN_ON_ONCE(rt_se->on_list);
|
|
|
|
if (flags & ENQUEUE_HEAD)
|
|
|
|
list_add(&rt_se->run_list, queue);
|
|
|
|
else
|
|
|
|
list_add_tail(&rt_se->run_list, queue);
|
|
|
|
|
|
|
|
__set_bit(rt_se_prio(rt_se), array->bitmap);
|
|
|
|
rt_se->on_list = 1;
|
|
|
|
}
|
|
|
|
rt_se->on_rq = 1;
|
2008-01-25 20:08:27 +00:00
|
|
|
|
2008-01-25 20:08:30 +00:00
|
|
|
inc_rt_tasks(rt_se, rt_rq);
|
|
|
|
}
|
|
|
|
|
2016-01-18 14:27:07 +00:00
|
|
|
static void __dequeue_rt_entity(struct sched_rt_entity *rt_se, unsigned int flags)
|
2008-01-25 20:08:30 +00:00
|
|
|
{
|
|
|
|
struct rt_rq *rt_rq = rt_rq_of_se(rt_se);
|
|
|
|
struct rt_prio_array *array = &rt_rq->active;
|
|
|
|
|
2016-01-18 14:27:07 +00:00
|
|
|
if (move_entity(flags)) {
|
|
|
|
WARN_ON_ONCE(!rt_se->on_list);
|
|
|
|
__delist_rt_entity(rt_se, array);
|
|
|
|
}
|
|
|
|
rt_se->on_rq = 0;
|
2008-01-25 20:08:30 +00:00
|
|
|
|
|
|
|
dec_rt_tasks(rt_se, rt_rq);
|
|
|
|
}
|
|
|
|
|
|
|
|
/*
|
|
|
|
* Because the prio of an upper entry depends on the lower
|
|
|
|
* entries, we must remove entries top - down.
|
|
|
|
*/
|
2016-01-18 14:27:07 +00:00
|
|
|
static void dequeue_rt_stack(struct sched_rt_entity *rt_se, unsigned int flags)
|
2008-01-25 20:08:30 +00:00
|
|
|
{
|
2008-06-19 07:06:57 +00:00
|
|
|
struct sched_rt_entity *back = NULL;
|
2022-06-28 09:22:59 +00:00
|
|
|
unsigned int rt_nr_running;
|
2008-01-25 20:08:30 +00:00
|
|
|
|
2008-04-19 17:45:00 +00:00
|
|
|
for_each_sched_rt_entity(rt_se) {
|
|
|
|
rt_se->back = back;
|
|
|
|
back = rt_se;
|
|
|
|
}
|
|
|
|
|
2022-06-28 09:22:59 +00:00
|
|
|
rt_nr_running = rt_rq_of_se(back)->rt_nr_running;
|
2014-03-14 22:15:00 +00:00
|
|
|
|
2008-04-19 17:45:00 +00:00
|
|
|
for (rt_se = back; rt_se; rt_se = rt_se->back) {
|
|
|
|
if (on_rt_rq(rt_se))
|
2016-01-18 14:27:07 +00:00
|
|
|
__dequeue_rt_entity(rt_se, flags);
|
2008-06-19 07:06:57 +00:00
|
|
|
}
|
2022-06-28 09:22:59 +00:00
|
|
|
|
|
|
|
dequeue_top_rt_rq(rt_rq_of_se(back), rt_nr_running);
|
2008-06-19 07:06:57 +00:00
|
|
|
}
|
|
|
|
|
2016-01-18 14:27:07 +00:00
|
|
|
static void enqueue_rt_entity(struct sched_rt_entity *rt_se, unsigned int flags)
|
2008-06-19 07:06:57 +00:00
|
|
|
{
|
2014-03-14 22:15:00 +00:00
|
|
|
struct rq *rq = rq_of_rt_se(rt_se);
|
|
|
|
|
sched/rt: Support schedstats for RT sched class
We want to measure the latency of RT tasks in our production
environment with schedstats facility, but currently schedstats is only
supported for fair sched class. This patch enable it for RT sched class
as well.
After we make the struct sched_statistics and the helpers of it
independent of fair sched class, we can easily use the schedstats
facility for RT sched class.
The schedstat usage in RT sched class is similar with fair sched class,
for example,
fair RT
enqueue update_stats_enqueue_fair update_stats_enqueue_rt
dequeue update_stats_dequeue_fair update_stats_dequeue_rt
put_prev_task update_stats_wait_start update_stats_wait_start_rt
set_next_task update_stats_wait_end update_stats_wait_end_rt
The user can get the schedstats information in the same way in fair sched
class. For example,
fair RT
/proc/[pid]/sched /proc/[pid]/sched
schedstats is not supported for RT group.
The output of a RT task's schedstats as follows,
$ cat /proc/10349/sched
...
sum_sleep_runtime : 972.434535
sum_block_runtime : 960.433522
wait_start : 188510.871584
sleep_start : 0.000000
block_start : 0.000000
sleep_max : 12.001013
block_max : 952.660622
exec_max : 0.049629
slice_max : 0.000000
wait_max : 0.018538
wait_sum : 0.424340
wait_count : 49
iowait_sum : 956.495640
iowait_count : 24
nr_migrations_cold : 0
nr_failed_migrations_affine : 0
nr_failed_migrations_running : 0
nr_failed_migrations_hot : 0
nr_forced_migrations : 0
nr_wakeups : 49
nr_wakeups_sync : 0
nr_wakeups_migrate : 0
nr_wakeups_local : 49
nr_wakeups_remote : 0
nr_wakeups_affine : 0
nr_wakeups_affine_attempts : 0
nr_wakeups_passive : 0
nr_wakeups_idle : 0
...
The sched:sched_stat_{wait, sleep, iowait, blocked} tracepoints can
be used to trace RT tasks as well. The output of these tracepoints for a
RT tasks as follows,
- runtime
stress-10352 [004] d.h. 1035.382286: sched_stat_runtime: comm=stress pid=10352 runtime=995769 [ns] vruntime=0 [ns]
[vruntime=0 means it is a RT task]
- wait
<idle>-0 [004] dN.. 1227.688544: sched_stat_wait: comm=stress pid=10352 delay=46849882 [ns]
- blocked
kworker/4:1-465 [004] dN.. 1585.676371: sched_stat_blocked: comm=stress pid=17194 delay=189963 [ns]
- iowait
kworker/4:1-465 [004] dN.. 1585.675330: sched_stat_iowait: comm=stress pid=17189 delay=182848 [ns]
- sleep
sleep-18194 [023] dN.. 1780.891840: sched_stat_sleep: comm=sleep.sh pid=17767 delay=1001160770 [ns]
sleep-18196 [023] dN.. 1781.893208: sched_stat_sleep: comm=sleep.sh pid=17767 delay=1001161970 [ns]
sleep-18197 [023] dN.. 1782.894544: sched_stat_sleep: comm=sleep.sh pid=17767 delay=1001128840 [ns]
[ In sleep.sh, it sleeps 1 sec each time. ]
[lkp@intel.com: reported build failure in earlier version]
Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20210905143547.4668-7-laoar.shao@gmail.com
2021-09-05 14:35:45 +00:00
|
|
|
update_stats_enqueue_rt(rt_rq_of_se(rt_se), rt_se, flags);
|
|
|
|
|
2016-01-18 14:27:07 +00:00
|
|
|
dequeue_rt_stack(rt_se, flags);
|
2008-06-19 07:06:57 +00:00
|
|
|
for_each_sched_rt_entity(rt_se)
|
2016-01-18 14:27:07 +00:00
|
|
|
__enqueue_rt_entity(rt_se, flags);
|
2014-03-14 22:15:00 +00:00
|
|
|
enqueue_top_rt_rq(&rq->rt);
|
2008-06-19 07:06:57 +00:00
|
|
|
}
|
|
|
|
|
2016-01-18 14:27:07 +00:00
|
|
|
static void dequeue_rt_entity(struct sched_rt_entity *rt_se, unsigned int flags)
|
2008-06-19 07:06:57 +00:00
|
|
|
{
|
2014-03-14 22:15:00 +00:00
|
|
|
struct rq *rq = rq_of_rt_se(rt_se);
|
|
|
|
|
sched/rt: Support schedstats for RT sched class
We want to measure the latency of RT tasks in our production
environment with schedstats facility, but currently schedstats is only
supported for fair sched class. This patch enable it for RT sched class
as well.
After we make the struct sched_statistics and the helpers of it
independent of fair sched class, we can easily use the schedstats
facility for RT sched class.
The schedstat usage in RT sched class is similar with fair sched class,
for example,
fair RT
enqueue update_stats_enqueue_fair update_stats_enqueue_rt
dequeue update_stats_dequeue_fair update_stats_dequeue_rt
put_prev_task update_stats_wait_start update_stats_wait_start_rt
set_next_task update_stats_wait_end update_stats_wait_end_rt
The user can get the schedstats information in the same way in fair sched
class. For example,
fair RT
/proc/[pid]/sched /proc/[pid]/sched
schedstats is not supported for RT group.
The output of a RT task's schedstats as follows,
$ cat /proc/10349/sched
...
sum_sleep_runtime : 972.434535
sum_block_runtime : 960.433522
wait_start : 188510.871584
sleep_start : 0.000000
block_start : 0.000000
sleep_max : 12.001013
block_max : 952.660622
exec_max : 0.049629
slice_max : 0.000000
wait_max : 0.018538
wait_sum : 0.424340
wait_count : 49
iowait_sum : 956.495640
iowait_count : 24
nr_migrations_cold : 0
nr_failed_migrations_affine : 0
nr_failed_migrations_running : 0
nr_failed_migrations_hot : 0
nr_forced_migrations : 0
nr_wakeups : 49
nr_wakeups_sync : 0
nr_wakeups_migrate : 0
nr_wakeups_local : 49
nr_wakeups_remote : 0
nr_wakeups_affine : 0
nr_wakeups_affine_attempts : 0
nr_wakeups_passive : 0
nr_wakeups_idle : 0
...
The sched:sched_stat_{wait, sleep, iowait, blocked} tracepoints can
be used to trace RT tasks as well. The output of these tracepoints for a
RT tasks as follows,
- runtime
stress-10352 [004] d.h. 1035.382286: sched_stat_runtime: comm=stress pid=10352 runtime=995769 [ns] vruntime=0 [ns]
[vruntime=0 means it is a RT task]
- wait
<idle>-0 [004] dN.. 1227.688544: sched_stat_wait: comm=stress pid=10352 delay=46849882 [ns]
- blocked
kworker/4:1-465 [004] dN.. 1585.676371: sched_stat_blocked: comm=stress pid=17194 delay=189963 [ns]
- iowait
kworker/4:1-465 [004] dN.. 1585.675330: sched_stat_iowait: comm=stress pid=17189 delay=182848 [ns]
- sleep
sleep-18194 [023] dN.. 1780.891840: sched_stat_sleep: comm=sleep.sh pid=17767 delay=1001160770 [ns]
sleep-18196 [023] dN.. 1781.893208: sched_stat_sleep: comm=sleep.sh pid=17767 delay=1001161970 [ns]
sleep-18197 [023] dN.. 1782.894544: sched_stat_sleep: comm=sleep.sh pid=17767 delay=1001128840 [ns]
[ In sleep.sh, it sleeps 1 sec each time. ]
[lkp@intel.com: reported build failure in earlier version]
Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20210905143547.4668-7-laoar.shao@gmail.com
2021-09-05 14:35:45 +00:00
|
|
|
update_stats_dequeue_rt(rt_rq_of_se(rt_se), rt_se, flags);
|
|
|
|
|
2016-01-18 14:27:07 +00:00
|
|
|
dequeue_rt_stack(rt_se, flags);
|
2008-06-19 07:06:57 +00:00
|
|
|
|
|
|
|
for_each_sched_rt_entity(rt_se) {
|
|
|
|
struct rt_rq *rt_rq = group_rt_rq(rt_se);
|
|
|
|
|
|
|
|
if (rt_rq && rt_rq->rt_nr_running)
|
2016-01-18 14:27:07 +00:00
|
|
|
__enqueue_rt_entity(rt_se, flags);
|
2008-04-19 17:45:00 +00:00
|
|
|
}
|
2014-03-14 22:15:00 +00:00
|
|
|
enqueue_top_rt_rq(&rq->rt);
|
2007-07-09 16:51:58 +00:00
|
|
|
}
|
|
|
|
|
|
|
|
/*
|
|
|
|
* Adding/removing a task to/from a priority array:
|
|
|
|
*/
|
2010-01-20 20:58:57 +00:00
|
|
|
static void
|
2010-03-24 15:38:48 +00:00
|
|
|
enqueue_task_rt(struct rq *rq, struct task_struct *p, int flags)
|
2008-01-25 20:08:30 +00:00
|
|
|
{
|
|
|
|
struct sched_rt_entity *rt_se = &p->rt;
|
|
|
|
|
2010-03-24 15:38:48 +00:00
|
|
|
if (flags & ENQUEUE_WAKEUP)
|
2008-01-25 20:08:30 +00:00
|
|
|
rt_se->timeout = 0;
|
|
|
|
|
sched/rt: Support schedstats for RT sched class
We want to measure the latency of RT tasks in our production
environment with schedstats facility, but currently schedstats is only
supported for fair sched class. This patch enable it for RT sched class
as well.
After we make the struct sched_statistics and the helpers of it
independent of fair sched class, we can easily use the schedstats
facility for RT sched class.
The schedstat usage in RT sched class is similar with fair sched class,
for example,
fair RT
enqueue update_stats_enqueue_fair update_stats_enqueue_rt
dequeue update_stats_dequeue_fair update_stats_dequeue_rt
put_prev_task update_stats_wait_start update_stats_wait_start_rt
set_next_task update_stats_wait_end update_stats_wait_end_rt
The user can get the schedstats information in the same way in fair sched
class. For example,
fair RT
/proc/[pid]/sched /proc/[pid]/sched
schedstats is not supported for RT group.
The output of a RT task's schedstats as follows,
$ cat /proc/10349/sched
...
sum_sleep_runtime : 972.434535
sum_block_runtime : 960.433522
wait_start : 188510.871584
sleep_start : 0.000000
block_start : 0.000000
sleep_max : 12.001013
block_max : 952.660622
exec_max : 0.049629
slice_max : 0.000000
wait_max : 0.018538
wait_sum : 0.424340
wait_count : 49
iowait_sum : 956.495640
iowait_count : 24
nr_migrations_cold : 0
nr_failed_migrations_affine : 0
nr_failed_migrations_running : 0
nr_failed_migrations_hot : 0
nr_forced_migrations : 0
nr_wakeups : 49
nr_wakeups_sync : 0
nr_wakeups_migrate : 0
nr_wakeups_local : 49
nr_wakeups_remote : 0
nr_wakeups_affine : 0
nr_wakeups_affine_attempts : 0
nr_wakeups_passive : 0
nr_wakeups_idle : 0
...
The sched:sched_stat_{wait, sleep, iowait, blocked} tracepoints can
be used to trace RT tasks as well. The output of these tracepoints for a
RT tasks as follows,
- runtime
stress-10352 [004] d.h. 1035.382286: sched_stat_runtime: comm=stress pid=10352 runtime=995769 [ns] vruntime=0 [ns]
[vruntime=0 means it is a RT task]
- wait
<idle>-0 [004] dN.. 1227.688544: sched_stat_wait: comm=stress pid=10352 delay=46849882 [ns]
- blocked
kworker/4:1-465 [004] dN.. 1585.676371: sched_stat_blocked: comm=stress pid=17194 delay=189963 [ns]
- iowait
kworker/4:1-465 [004] dN.. 1585.675330: sched_stat_iowait: comm=stress pid=17189 delay=182848 [ns]
- sleep
sleep-18194 [023] dN.. 1780.891840: sched_stat_sleep: comm=sleep.sh pid=17767 delay=1001160770 [ns]
sleep-18196 [023] dN.. 1781.893208: sched_stat_sleep: comm=sleep.sh pid=17767 delay=1001161970 [ns]
sleep-18197 [023] dN.. 1782.894544: sched_stat_sleep: comm=sleep.sh pid=17767 delay=1001128840 [ns]
[ In sleep.sh, it sleeps 1 sec each time. ]
[lkp@intel.com: reported build failure in earlier version]
Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20210905143547.4668-7-laoar.shao@gmail.com
2021-09-05 14:35:45 +00:00
|
|
|
check_schedstat_required();
|
|
|
|
update_stats_wait_start_rt(rt_rq_of_se(rt_se), rt_se);
|
|
|
|
|
2016-01-18 14:27:07 +00:00
|
|
|
enqueue_rt_entity(rt_se, flags);
|
2008-06-27 11:41:14 +00:00
|
|
|
|
2017-02-05 14:41:03 +00:00
|
|
|
if (!task_current(rq, p) && p->nr_cpus_allowed > 1)
|
sched: create "pushable_tasks" list to limit pushing to one attempt
The RT scheduler employs a "push/pull" design to actively balance tasks
within the system (on a per disjoint cpuset basis). When a task is
awoken, it is immediately determined if there are any lower priority
cpus which should be preempted. This is opposed to the way normal
SCHED_OTHER tasks behave, which will wait for a periodic rebalancing
operation to occur before spreading out load.
When a particular RQ has more than 1 active RT task, it is said to
be in an "overloaded" state. Once this occurs, the system enters
the active balancing mode, where it will try to push the task away,
or persuade a different cpu to pull it over. The system will stay
in this state until the system falls back below the <= 1 queued RT
task per RQ.
However, the current implementation suffers from a limitation in the
push logic. Once overloaded, all tasks (other than current) on the
RQ are analyzed on every push operation, even if it was previously
unpushable (due to affinity, etc). Whats more, the operation stops
at the first task that is unpushable and will not look at items
lower in the queue. This causes two problems:
1) We can have the same tasks analyzed over and over again during each
push, which extends out the fast path in the scheduler for no
gain. Consider a RQ that has dozens of tasks that are bound to a
core. Each one of those tasks will be encountered and skipped
for each push operation while they are queued.
2) There may be lower-priority tasks under the unpushable task that
could have been successfully pushed, but will never be considered
until either the unpushable task is cleared, or a pull operation
succeeds. The net result is a potential latency source for mid
priority tasks.
This patch aims to rectify these two conditions by introducing a new
priority sorted list: "pushable_tasks". A task is added to the list
each time a task is activated or preempted. It is removed from the
list any time it is deactivated, made current, or fails to push.
This works because a task only needs to be attempted to push once.
After an initial failure to push, the other cpus will eventually try to
pull the task when the conditions are proper. This also solves the
problem that we don't completely analyze all tasks due to encountering
an unpushable tasks. Now every task will have a push attempted (when
appropriate).
This reduces latency both by shorting the critical section of the
rq->lock for certain workloads, and by making sure the algorithm
considers all eligible tasks in the system.
[ rostedt: added a couple more BUG_ONs ]
Signed-off-by: Gregory Haskins <ghaskins@novell.com>
Acked-by: Steven Rostedt <srostedt@redhat.com>
2008-12-29 14:39:53 +00:00
|
|
|
enqueue_pushable_task(rq, p);
|
2008-01-25 20:08:30 +00:00
|
|
|
}
|
|
|
|
|
2010-03-24 15:38:48 +00:00
|
|
|
static void dequeue_task_rt(struct rq *rq, struct task_struct *p, int flags)
|
2007-07-09 16:51:58 +00:00
|
|
|
{
|
2008-01-25 20:08:30 +00:00
|
|
|
struct sched_rt_entity *rt_se = &p->rt;
|
2007-07-09 16:51:58 +00:00
|
|
|
|
2007-08-09 09:16:48 +00:00
|
|
|
update_curr_rt(rq);
|
2016-01-18 14:27:07 +00:00
|
|
|
dequeue_rt_entity(rt_se, flags);
|
2008-06-27 11:41:14 +00:00
|
|
|
|
sched: create "pushable_tasks" list to limit pushing to one attempt
The RT scheduler employs a "push/pull" design to actively balance tasks
within the system (on a per disjoint cpuset basis). When a task is
awoken, it is immediately determined if there are any lower priority
cpus which should be preempted. This is opposed to the way normal
SCHED_OTHER tasks behave, which will wait for a periodic rebalancing
operation to occur before spreading out load.
When a particular RQ has more than 1 active RT task, it is said to
be in an "overloaded" state. Once this occurs, the system enters
the active balancing mode, where it will try to push the task away,
or persuade a different cpu to pull it over. The system will stay
in this state until the system falls back below the <= 1 queued RT
task per RQ.
However, the current implementation suffers from a limitation in the
push logic. Once overloaded, all tasks (other than current) on the
RQ are analyzed on every push operation, even if it was previously
unpushable (due to affinity, etc). Whats more, the operation stops
at the first task that is unpushable and will not look at items
lower in the queue. This causes two problems:
1) We can have the same tasks analyzed over and over again during each
push, which extends out the fast path in the scheduler for no
gain. Consider a RQ that has dozens of tasks that are bound to a
core. Each one of those tasks will be encountered and skipped
for each push operation while they are queued.
2) There may be lower-priority tasks under the unpushable task that
could have been successfully pushed, but will never be considered
until either the unpushable task is cleared, or a pull operation
succeeds. The net result is a potential latency source for mid
priority tasks.
This patch aims to rectify these two conditions by introducing a new
priority sorted list: "pushable_tasks". A task is added to the list
each time a task is activated or preempted. It is removed from the
list any time it is deactivated, made current, or fails to push.
This works because a task only needs to be attempted to push once.
After an initial failure to push, the other cpus will eventually try to
pull the task when the conditions are proper. This also solves the
problem that we don't completely analyze all tasks due to encountering
an unpushable tasks. Now every task will have a push attempted (when
appropriate).
This reduces latency both by shorting the critical section of the
rq->lock for certain workloads, and by making sure the algorithm
considers all eligible tasks in the system.
[ rostedt: added a couple more BUG_ONs ]
Signed-off-by: Gregory Haskins <ghaskins@novell.com>
Acked-by: Steven Rostedt <srostedt@redhat.com>
2008-12-29 14:39:53 +00:00
|
|
|
dequeue_pushable_task(rq, p);
|
2007-07-09 16:51:58 +00:00
|
|
|
}
|
|
|
|
|
|
|
|
/*
|
2011-11-12 17:07:57 +00:00
|
|
|
* Put task to the head or the end of the run list without the overhead of
|
|
|
|
* dequeue followed by enqueue.
|
2007-07-09 16:51:58 +00:00
|
|
|
*/
|
2008-07-01 21:32:15 +00:00
|
|
|
static void
|
|
|
|
requeue_rt_entity(struct rt_rq *rt_rq, struct sched_rt_entity *rt_se, int head)
|
2008-01-25 20:08:30 +00:00
|
|
|
{
|
2008-06-19 07:09:15 +00:00
|
|
|
if (on_rt_rq(rt_se)) {
|
2008-07-01 21:32:15 +00:00
|
|
|
struct rt_prio_array *array = &rt_rq->active;
|
|
|
|
struct list_head *queue = array->queue + rt_se_prio(rt_se);
|
|
|
|
|
|
|
|
if (head)
|
|
|
|
list_move(&rt_se->run_list, queue);
|
|
|
|
else
|
|
|
|
list_move_tail(&rt_se->run_list, queue);
|
2008-06-19 07:09:15 +00:00
|
|
|
}
|
2008-01-25 20:08:30 +00:00
|
|
|
}
|
|
|
|
|
2008-07-01 21:32:15 +00:00
|
|
|
static void requeue_task_rt(struct rq *rq, struct task_struct *p, int head)
|
2007-07-09 16:51:58 +00:00
|
|
|
{
|
2008-01-25 20:08:30 +00:00
|
|
|
struct sched_rt_entity *rt_se = &p->rt;
|
|
|
|
struct rt_rq *rt_rq;
|
2007-07-09 16:51:58 +00:00
|
|
|
|
2008-01-25 20:08:30 +00:00
|
|
|
for_each_sched_rt_entity(rt_se) {
|
|
|
|
rt_rq = rt_rq_of_se(rt_se);
|
2008-07-01 21:32:15 +00:00
|
|
|
requeue_rt_entity(rt_rq, rt_se, head);
|
2008-01-25 20:08:30 +00:00
|
|
|
}
|
2007-07-09 16:51:58 +00:00
|
|
|
}
|
|
|
|
|
2008-01-25 20:08:30 +00:00
|
|
|
static void yield_task_rt(struct rq *rq)
|
2007-07-09 16:51:58 +00:00
|
|
|
{
|
2008-07-01 21:32:15 +00:00
|
|
|
requeue_task_rt(rq, rq->curr, 0);
|
2007-07-09 16:51:58 +00:00
|
|
|
}
|
|
|
|
|
2008-01-25 20:08:09 +00:00
|
|
|
#ifdef CONFIG_SMP
|
2008-01-25 20:08:10 +00:00
|
|
|
static int find_lowest_rq(struct task_struct *task);
|
|
|
|
|
2010-03-24 17:34:10 +00:00
|
|
|
static int
|
2020-11-02 18:45:13 +00:00
|
|
|
select_task_rq_rt(struct task_struct *p, int cpu, int flags)
|
2008-01-25 20:08:09 +00:00
|
|
|
{
|
2011-04-05 15:23:46 +00:00
|
|
|
struct task_struct *curr;
|
|
|
|
struct rq *rq;
|
2019-10-09 10:46:11 +00:00
|
|
|
bool test;
|
2011-06-17 01:55:22 +00:00
|
|
|
|
|
|
|
/* For anything but wake ups, just return the task_cpu */
|
2020-11-02 18:45:13 +00:00
|
|
|
if (!(flags & (WF_TTWU | WF_FORK)))
|
2011-06-17 01:55:22 +00:00
|
|
|
goto out;
|
|
|
|
|
2011-04-05 15:23:46 +00:00
|
|
|
rq = cpu_rq(cpu);
|
|
|
|
|
|
|
|
rcu_read_lock();
|
2015-04-28 20:00:20 +00:00
|
|
|
curr = READ_ONCE(rq->curr); /* unlocked access */
|
2011-04-05 15:23:46 +00:00
|
|
|
|
2008-01-25 20:08:10 +00:00
|
|
|
/*
|
2011-04-05 15:23:46 +00:00
|
|
|
* If the current task on @p's runqueue is an RT task, then
|
2008-01-25 20:08:12 +00:00
|
|
|
* try to see if we can wake this RT task up on another
|
|
|
|
* runqueue. Otherwise simply start this RT task
|
|
|
|
* on its current runqueue.
|
|
|
|
*
|
sched: Try not to migrate higher priority RT tasks
When first working on the RT scheduler design, we concentrated on
keeping all CPUs running RT tasks instead of having multiple RT
tasks on a single CPU waiting for the migration thread to move
them. Instead we take a more proactive stance and push or pull RT
tasks from one CPU to another on wakeup or scheduling.
When an RT task wakes up on a CPU that is running another RT task,
instead of preempting it and killing the cache of the running RT
task, we look to see if we can migrate the RT task that is waking
up, even if the RT task waking up is of higher priority.
This may sound a bit odd, but RT tasks should be limited in
migration by the user anyway. But in practice, people do not do
this, which causes high prio RT tasks to bounce around the CPUs.
This becomes even worse when we have priority inheritance, because
a high prio task can block on a lower prio task and boost its
priority. When the lower prio task wakes up the high prio task, if
it happens to be on the same CPU it will migrate off of it.
But in reality, the above does not happen much either, because the
wake up of the lower prio task, which has already been boosted, if
it was on the same CPU as the higher prio task, it would then
migrate off of it. But anyway, we do not want to migrate them
either.
To examine the scheduling, I created a test program and examined it
under kernelshark. The test program created CPU * 2 threads, where
each thread had a different priority. The program takes different
options. The options used in this change log was to have priority
inheritance mutexes or not.
All threads did the following loop:
static void grab_lock(long id, int iter, int l)
{
ftrace_write("thread %ld iter %d, taking lock %d\n",
id, iter, l);
pthread_mutex_lock(&locks[l]);
ftrace_write("thread %ld iter %d, took lock %d\n",
id, iter, l);
busy_loop(nr_tasks - id);
ftrace_write("thread %ld iter %d, unlock lock %d\n",
id, iter, l);
pthread_mutex_unlock(&locks[l]);
}
void *start_task(void *id)
{
[...]
while (!done) {
for (l = 0; l < nr_locks; l++) {
grab_lock(id, i, l);
ftrace_write("thread %ld iter %d sleeping\n",
id, i);
ms_sleep(id);
}
i++;
}
[...]
}
The busy_loop(ms) keeps the CPU spinning for ms milliseconds. The
ms_sleep(ms) sleeps for ms milliseconds. The ftrace_write() writes
to the ftrace buffer to help analyze via ftrace.
The higher the id, the higher the prio, the shorter it does the
busy loop, but the longer it spins. This is usually the case with
RT tasks, the lower priority tasks usually run longer than higher
priority tasks.
At the end of the test, it records the number of loops each thread
took, as well as the number of voluntary preemptions, non-voluntary
preemptions, and number of migrations each thread took, taking the
information from /proc/$$/sched and /proc/$$/status.
Running this on a 4 CPU processor, the results without changes to
the kernel looked like this:
Task vol nonvol migrated iterations
---- --- ------ -------- ----------
0: 53 3220 1470 98
1: 562 773 724 98
2: 752 933 1375 98
3: 749 39 697 98
4: 758 5 515 98
5: 764 2 679 99
6: 761 2 535 99
7: 757 3 346 99
total: 5156 4977 6341 787
Each thread regardless of priority migrated a few hundred times.
The higher priority tasks, were a little better but still took
quite an impact.
By letting higher priority tasks bump the lower prio task from the
CPU, things changed a bit:
Task vol nonvol migrated iterations
---- --- ------ -------- ----------
0: 37 2835 1937 98
1: 666 1821 1865 98
2: 654 1003 1385 98
3: 664 635 973 99
4: 698 197 352 99
5: 703 101 159 99
6: 708 1 75 99
7: 713 1 2 99
total: 4843 6594 6748 789
The total # of migrations did not change (several runs showed the
difference all within the noise). But we now see a dramatic
improvement to the higher priority tasks. (kernelshark showed that
the watchdog timer bumped the highest priority task to give it the
2 count. This was actually consistent with every run).
Notice that the # of iterations did not change either.
The above was with priority inheritance mutexes. That is, when the
higher prority task blocked on a lower priority task, the lower
priority task would inherit the higher priority task (which shows
why task 6 was bumped so many times). When not using priority
inheritance mutexes, the current kernel shows this:
Task vol nonvol migrated iterations
---- --- ------ -------- ----------
0: 56 3101 1892 95
1: 594 713 937 95
2: 625 188 618 95
3: 628 4 491 96
4: 640 7 468 96
5: 631 2 501 96
6: 641 1 466 96
7: 643 2 497 96
total: 4458 4018 5870 765
Not much changed with or without priority inheritance mutexes. But
if we let the high priority task bump lower priority tasks on
wakeup we see:
Task vol nonvol migrated iterations
---- --- ------ -------- ----------
0: 115 3439 2782 98
1: 633 1354 1583 99
2: 652 919 1218 99
3: 645 713 934 99
4: 690 3 3 99
5: 694 1 4 99
6: 720 3 4 99
7: 747 0 1 100
Which shows a even bigger change. The big difference between task 3
and task 4 is because we have only 4 CPUs on the machine, causing
the 4 highest prio tasks to always have preference.
Although I did not measure cache misses, and I'm sure there would
be little to measure since the test was not data intensive, I could
imagine large improvements for higher priority tasks when dealing
with lower priority tasks. Thus, I'm satisfied with making the
change and agreeing with what Gregory Haskins argued a few years
ago when we first had this discussion.
One final note. All tasks in the above tests were RT tasks. Any RT
task will always preempt a non RT task that is running on the CPU
the RT task wants to run on.
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Gregory Haskins <ghaskins@novell.com>
LKML-Reference: <20100921024138.605460343@goodmis.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2010-09-21 02:40:03 +00:00
|
|
|
* We want to avoid overloading runqueues. If the woken
|
|
|
|
* task is a higher priority, then it will stay on this CPU
|
|
|
|
* and the lower prio task should be moved to another CPU.
|
|
|
|
* Even though this will probably make the lower prio task
|
|
|
|
* lose its cache, we do not want to bounce a higher task
|
|
|
|
* around just because it gave up its CPU, perhaps for a
|
|
|
|
* lock?
|
|
|
|
*
|
|
|
|
* For equal prio tasks, we just let the scheduler sort it out.
|
2011-04-05 15:23:46 +00:00
|
|
|
*
|
|
|
|
* Otherwise, just let it ride on the affined RQ and the
|
|
|
|
* post-schedule router will push the preempted task away
|
|
|
|
*
|
|
|
|
* This test is optimistic, if we get it wrong the load-balancer
|
|
|
|
* will have to sort it out.
|
2019-10-09 10:46:11 +00:00
|
|
|
*
|
|
|
|
* We take into account the capacity of the CPU to ensure it fits the
|
|
|
|
* requirement of the task - which is only important on heterogeneous
|
|
|
|
* systems like big.LITTLE.
|
2008-01-25 20:08:10 +00:00
|
|
|
*/
|
2019-10-09 10:46:11 +00:00
|
|
|
test = curr &&
|
|
|
|
unlikely(rt_task(curr)) &&
|
|
|
|
(curr->nr_cpus_allowed < 2 || curr->prio <= p->prio);
|
|
|
|
|
|
|
|
if (test || !rt_task_fits_capacity(p, cpu)) {
|
2011-04-05 15:23:46 +00:00
|
|
|
int target = find_lowest_rq(p);
|
2008-01-25 20:08:10 +00:00
|
|
|
|
2020-03-02 13:27:17 +00:00
|
|
|
/*
|
|
|
|
* Bail out if we were forcing a migration to find a better
|
|
|
|
* fitting CPU but our search failed.
|
|
|
|
*/
|
|
|
|
if (!test && target != -1 && !rt_task_fits_capacity(p, target))
|
|
|
|
goto out_unlock;
|
|
|
|
|
2014-12-12 23:38:12 +00:00
|
|
|
/*
|
|
|
|
* Don't bother moving it if the destination CPU is
|
|
|
|
* not running a lower priority task.
|
|
|
|
*/
|
|
|
|
if (target != -1 &&
|
|
|
|
p->prio < cpu_rq(target)->rt.highest_prio.curr)
|
2011-04-05 15:23:46 +00:00
|
|
|
cpu = target;
|
2008-01-25 20:08:10 +00:00
|
|
|
}
|
2020-03-02 13:27:17 +00:00
|
|
|
|
|
|
|
out_unlock:
|
2011-04-05 15:23:46 +00:00
|
|
|
rcu_read_unlock();
|
2008-01-25 20:08:10 +00:00
|
|
|
|
2011-06-17 01:55:22 +00:00
|
|
|
out:
|
2011-04-05 15:23:46 +00:00
|
|
|
return cpu;
|
2008-01-25 20:08:09 +00:00
|
|
|
}
|
2008-07-01 21:32:15 +00:00
|
|
|
|
|
|
|
static void check_preempt_equal_prio(struct rq *rq, struct task_struct *p)
|
|
|
|
{
|
2014-10-30 22:39:31 +00:00
|
|
|
/*
|
|
|
|
* Current can't be migrated, useless to reschedule,
|
|
|
|
* let's hope p can move out.
|
|
|
|
*/
|
2017-02-05 14:41:03 +00:00
|
|
|
if (rq->curr->nr_cpus_allowed == 1 ||
|
2020-03-02 13:27:18 +00:00
|
|
|
!cpupri_find(&rq->rd->cpupri, rq->curr, NULL))
|
2008-07-01 21:32:15 +00:00
|
|
|
return;
|
|
|
|
|
2014-10-30 22:39:31 +00:00
|
|
|
/*
|
|
|
|
* p is migratable, so let's not schedule it and
|
|
|
|
* see if it is pushed or pulled somewhere else.
|
|
|
|
*/
|
2019-10-09 10:46:11 +00:00
|
|
|
if (p->nr_cpus_allowed != 1 &&
|
2020-03-02 13:27:18 +00:00
|
|
|
cpupri_find(&rq->rd->cpupri, p, NULL))
|
2009-03-25 04:31:22 +00:00
|
|
|
return;
|
2008-11-24 16:05:13 +00:00
|
|
|
|
2008-07-01 21:32:15 +00:00
|
|
|
/*
|
sched: Clean up and harmonize the coding style of the scheduler code base
A good number of small style inconsistencies have accumulated
in the scheduler core, so do a pass over them to harmonize
all these details:
- fix speling in comments,
- use curly braces for multi-line statements,
- remove unnecessary parentheses from integer literals,
- capitalize consistently,
- remove stray newlines,
- add comments where necessary,
- remove invalid/unnecessary comments,
- align structure definitions and other data types vertically,
- add missing newlines for increased readability,
- fix vertical tabulation where it's misaligned,
- harmonize preprocessor conditional block labeling
and vertical alignment,
- remove line-breaks where they uglify the code,
- add newline after local variable definitions,
No change in functionality:
md5:
1191fa0a890cfa8132156d2959d7e9e2 built-in.o.before.asm
1191fa0a890cfa8132156d2959d7e9e2 built-in.o.after.asm
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-03-03 13:01:12 +00:00
|
|
|
* There appear to be other CPUs that can accept
|
|
|
|
* the current task but none can run 'p', so lets reschedule
|
|
|
|
* to try and push the current task away:
|
2008-07-01 21:32:15 +00:00
|
|
|
*/
|
|
|
|
requeue_task_rt(rq, p, 1);
|
2014-06-28 20:03:57 +00:00
|
|
|
resched_curr(rq);
|
2008-07-01 21:32:15 +00:00
|
|
|
}
|
|
|
|
|
2019-11-08 10:11:52 +00:00
|
|
|
static int balance_rt(struct rq *rq, struct task_struct *p, struct rq_flags *rf)
|
|
|
|
{
|
|
|
|
if (!on_rt_rq(&p->rt) && need_pull_rt_task(rq, p)) {
|
|
|
|
/*
|
|
|
|
* This is OK, because current is on_cpu, which avoids it being
|
|
|
|
* picked for load-balance and preemption/IRQs are still
|
|
|
|
* disabled avoiding further scheduler activity on it and we've
|
|
|
|
* not yet started the picking loop.
|
|
|
|
*/
|
|
|
|
rq_unpin_lock(rq, rf);
|
|
|
|
pull_rt_task(rq);
|
|
|
|
rq_repin_lock(rq, rf);
|
|
|
|
}
|
|
|
|
|
|
|
|
return sched_stop_runnable(rq) || sched_dl_runnable(rq) || sched_rt_runnable(rq);
|
|
|
|
}
|
2008-01-25 20:08:09 +00:00
|
|
|
#endif /* CONFIG_SMP */
|
|
|
|
|
2007-07-09 16:51:58 +00:00
|
|
|
/*
|
|
|
|
* Preempt the current task with a newly woken task if needed:
|
|
|
|
*/
|
2009-09-14 17:55:44 +00:00
|
|
|
static void check_preempt_curr_rt(struct rq *rq, struct task_struct *p, int flags)
|
2007-07-09 16:51:58 +00:00
|
|
|
{
|
sched: prioritize non-migratable tasks over migratable ones
Dmitry Adamushko pointed out a known flaw in the rt-balancing algorithm
that could allow suboptimal balancing if a non-migratable task gets
queued behind a running migratable one. It is discussed in this thread:
http://lkml.org/lkml/2008/4/22/296
This issue has been further exacerbated by a recent checkin to
sched-devel (git-id 5eee63a5ebc19a870ac40055c0be49457f3a89a3).
>From a pure priority standpoint, the run-queue is doing the "right"
thing. Using Dmitry's nomenclature, if T0 is on cpu1 first, and T1
wakes up at equal or lower priority (affined only to cpu1) later, it
*should* wait for T0 to finish. However, in reality that is likely
suboptimal from a system perspective if there are other cores that
could allow T0 and T1 to run concurrently. Since T1 can not migrate,
the only choice for higher concurrency is to try to move T0. This is
not something we addessed in the recent rt-balancing re-work.
This patch tries to enhance the balancing algorithm by accomodating this
scenario. It accomplishes this by incorporating the migratability of a
task into its priority calculation. Within a numerical tsk->prio, a
non-migratable task is logically higher than a migratable one. We
maintain this by introducing a new per-priority queue (xqueue, or
exclusive-queue) for holding non-migratable tasks. The scheduler will
draw from the xqueue over the standard shared-queue (squeue) when
available.
There are several details for utilizing this properly.
1) During task-wake-up, we not only need to check if the priority
preempts the current task, but we also need to check for this
non-migratable condition. Therefore, if a non-migratable task wakes
up and sees an equal priority migratable task already running, it
will attempt to preempt it *if* there is a likelyhood that the
current task will find an immediate home.
2) Tasks only get this non-migratable "priority boost" on wake-up. Any
requeuing will result in the non-migratable task being queued to the
end of the shared queue. This is an attempt to prevent the system
from being completely unfair to migratable tasks during things like
SCHED_RR timeslicing.
I am sure this patch introduces potentially "odd" behavior if you
concoct a scenario where a bunch of non-migratable threads could starve
migratable ones given the right pattern. I am not yet convinced that
this is a problem since we are talking about tasks of equal RT priority
anyway, and there never is much in the way of guarantees against
starvation under that scenario anyway. (e.g. you could come up with a
similar scenario with a specific timing environment verses an affinity
environment). I can be convinced otherwise, but for now I think this is
"ok".
Signed-off-by: Gregory Haskins <ghaskins@novell.com>
CC: Dmitry Adamushko <dmitry.adamushko@gmail.com>
CC: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
2008-05-12 19:20:41 +00:00
|
|
|
if (p->prio < rq->curr->prio) {
|
2014-06-28 20:03:57 +00:00
|
|
|
resched_curr(rq);
|
sched: prioritize non-migratable tasks over migratable ones
Dmitry Adamushko pointed out a known flaw in the rt-balancing algorithm
that could allow suboptimal balancing if a non-migratable task gets
queued behind a running migratable one. It is discussed in this thread:
http://lkml.org/lkml/2008/4/22/296
This issue has been further exacerbated by a recent checkin to
sched-devel (git-id 5eee63a5ebc19a870ac40055c0be49457f3a89a3).
>From a pure priority standpoint, the run-queue is doing the "right"
thing. Using Dmitry's nomenclature, if T0 is on cpu1 first, and T1
wakes up at equal or lower priority (affined only to cpu1) later, it
*should* wait for T0 to finish. However, in reality that is likely
suboptimal from a system perspective if there are other cores that
could allow T0 and T1 to run concurrently. Since T1 can not migrate,
the only choice for higher concurrency is to try to move T0. This is
not something we addessed in the recent rt-balancing re-work.
This patch tries to enhance the balancing algorithm by accomodating this
scenario. It accomplishes this by incorporating the migratability of a
task into its priority calculation. Within a numerical tsk->prio, a
non-migratable task is logically higher than a migratable one. We
maintain this by introducing a new per-priority queue (xqueue, or
exclusive-queue) for holding non-migratable tasks. The scheduler will
draw from the xqueue over the standard shared-queue (squeue) when
available.
There are several details for utilizing this properly.
1) During task-wake-up, we not only need to check if the priority
preempts the current task, but we also need to check for this
non-migratable condition. Therefore, if a non-migratable task wakes
up and sees an equal priority migratable task already running, it
will attempt to preempt it *if* there is a likelyhood that the
current task will find an immediate home.
2) Tasks only get this non-migratable "priority boost" on wake-up. Any
requeuing will result in the non-migratable task being queued to the
end of the shared queue. This is an attempt to prevent the system
from being completely unfair to migratable tasks during things like
SCHED_RR timeslicing.
I am sure this patch introduces potentially "odd" behavior if you
concoct a scenario where a bunch of non-migratable threads could starve
migratable ones given the right pattern. I am not yet convinced that
this is a problem since we are talking about tasks of equal RT priority
anyway, and there never is much in the way of guarantees against
starvation under that scenario anyway. (e.g. you could come up with a
similar scenario with a specific timing environment verses an affinity
environment). I can be convinced otherwise, but for now I think this is
"ok".
Signed-off-by: Gregory Haskins <ghaskins@novell.com>
CC: Dmitry Adamushko <dmitry.adamushko@gmail.com>
CC: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
2008-05-12 19:20:41 +00:00
|
|
|
return;
|
|
|
|
}
|
|
|
|
|
|
|
|
#ifdef CONFIG_SMP
|
|
|
|
/*
|
|
|
|
* If:
|
|
|
|
*
|
|
|
|
* - the newly woken task is of equal priority to the current task
|
|
|
|
* - the newly woken task is non-migratable while current is migratable
|
|
|
|
* - current will be preempted on the next reschedule
|
|
|
|
*
|
|
|
|
* we should check to see if current can readily move to a different
|
|
|
|
* cpu. If so, we will reschedule to allow the push logic to try
|
|
|
|
* to move current somewhere else, making room for our non-migratable
|
|
|
|
* task.
|
|
|
|
*/
|
2011-06-14 22:36:24 +00:00
|
|
|
if (p->prio == rq->curr->prio && !test_tsk_need_resched(rq->curr))
|
2008-07-01 21:32:15 +00:00
|
|
|
check_preempt_equal_prio(rq, p);
|
sched: prioritize non-migratable tasks over migratable ones
Dmitry Adamushko pointed out a known flaw in the rt-balancing algorithm
that could allow suboptimal balancing if a non-migratable task gets
queued behind a running migratable one. It is discussed in this thread:
http://lkml.org/lkml/2008/4/22/296
This issue has been further exacerbated by a recent checkin to
sched-devel (git-id 5eee63a5ebc19a870ac40055c0be49457f3a89a3).
>From a pure priority standpoint, the run-queue is doing the "right"
thing. Using Dmitry's nomenclature, if T0 is on cpu1 first, and T1
wakes up at equal or lower priority (affined only to cpu1) later, it
*should* wait for T0 to finish. However, in reality that is likely
suboptimal from a system perspective if there are other cores that
could allow T0 and T1 to run concurrently. Since T1 can not migrate,
the only choice for higher concurrency is to try to move T0. This is
not something we addessed in the recent rt-balancing re-work.
This patch tries to enhance the balancing algorithm by accomodating this
scenario. It accomplishes this by incorporating the migratability of a
task into its priority calculation. Within a numerical tsk->prio, a
non-migratable task is logically higher than a migratable one. We
maintain this by introducing a new per-priority queue (xqueue, or
exclusive-queue) for holding non-migratable tasks. The scheduler will
draw from the xqueue over the standard shared-queue (squeue) when
available.
There are several details for utilizing this properly.
1) During task-wake-up, we not only need to check if the priority
preempts the current task, but we also need to check for this
non-migratable condition. Therefore, if a non-migratable task wakes
up and sees an equal priority migratable task already running, it
will attempt to preempt it *if* there is a likelyhood that the
current task will find an immediate home.
2) Tasks only get this non-migratable "priority boost" on wake-up. Any
requeuing will result in the non-migratable task being queued to the
end of the shared queue. This is an attempt to prevent the system
from being completely unfair to migratable tasks during things like
SCHED_RR timeslicing.
I am sure this patch introduces potentially "odd" behavior if you
concoct a scenario where a bunch of non-migratable threads could starve
migratable ones given the right pattern. I am not yet convinced that
this is a problem since we are talking about tasks of equal RT priority
anyway, and there never is much in the way of guarantees against
starvation under that scenario anyway. (e.g. you could come up with a
similar scenario with a specific timing environment verses an affinity
environment). I can be convinced otherwise, but for now I think this is
"ok".
Signed-off-by: Gregory Haskins <ghaskins@novell.com>
CC: Dmitry Adamushko <dmitry.adamushko@gmail.com>
CC: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
2008-05-12 19:20:41 +00:00
|
|
|
#endif
|
2007-07-09 16:51:58 +00:00
|
|
|
}
|
|
|
|
|
2019-11-08 13:16:00 +00:00
|
|
|
static inline void set_next_task_rt(struct rq *rq, struct task_struct *p, bool first)
|
sched/core: Introduce set_next_task() helper for better code readability
When we pick the next task, we will do the following for the task:
1) p->se.exec_start = rq_clock_task(rq);
2) dequeue_pushable(_dl)_task(rq, p);
When we call set_curr_task(), we also need to do the same thing
above. In rt.c, the code at 1) is in the _pick_next_task_rt()
and the code at 2) is in the pick_next_task_rt(). If we put two
operations in one function, maybe better. So, we introduce a new
function set_next_task(), which is responsible for doing the above.
By introducing the function we can get rid of calling the
dequeue_pushable(_dl)_task() directly(We can call set_next_task())
in pick_next_task() and have better code readability and reuse.
In set_curr_task_rt(), we also can call set_next_task().
Do this things such that we end up with:
static struct task_struct *pick_next_task(struct rq *rq,
struct task_struct *prev,
struct rq_flags *rf)
{
/* do something else ... */
put_prev_task(rq, prev);
/* pick next task p */
set_next_task(rq, p);
/* do something else ... */
}
put_prev_task() can match set_next_task(), which can make the
code more readable.
Signed-off-by: Muchun Song <smuchun@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20181026131743.21786-1-smuchun@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-10-26 13:17:43 +00:00
|
|
|
{
|
sched/rt: Support schedstats for RT sched class
We want to measure the latency of RT tasks in our production
environment with schedstats facility, but currently schedstats is only
supported for fair sched class. This patch enable it for RT sched class
as well.
After we make the struct sched_statistics and the helpers of it
independent of fair sched class, we can easily use the schedstats
facility for RT sched class.
The schedstat usage in RT sched class is similar with fair sched class,
for example,
fair RT
enqueue update_stats_enqueue_fair update_stats_enqueue_rt
dequeue update_stats_dequeue_fair update_stats_dequeue_rt
put_prev_task update_stats_wait_start update_stats_wait_start_rt
set_next_task update_stats_wait_end update_stats_wait_end_rt
The user can get the schedstats information in the same way in fair sched
class. For example,
fair RT
/proc/[pid]/sched /proc/[pid]/sched
schedstats is not supported for RT group.
The output of a RT task's schedstats as follows,
$ cat /proc/10349/sched
...
sum_sleep_runtime : 972.434535
sum_block_runtime : 960.433522
wait_start : 188510.871584
sleep_start : 0.000000
block_start : 0.000000
sleep_max : 12.001013
block_max : 952.660622
exec_max : 0.049629
slice_max : 0.000000
wait_max : 0.018538
wait_sum : 0.424340
wait_count : 49
iowait_sum : 956.495640
iowait_count : 24
nr_migrations_cold : 0
nr_failed_migrations_affine : 0
nr_failed_migrations_running : 0
nr_failed_migrations_hot : 0
nr_forced_migrations : 0
nr_wakeups : 49
nr_wakeups_sync : 0
nr_wakeups_migrate : 0
nr_wakeups_local : 49
nr_wakeups_remote : 0
nr_wakeups_affine : 0
nr_wakeups_affine_attempts : 0
nr_wakeups_passive : 0
nr_wakeups_idle : 0
...
The sched:sched_stat_{wait, sleep, iowait, blocked} tracepoints can
be used to trace RT tasks as well. The output of these tracepoints for a
RT tasks as follows,
- runtime
stress-10352 [004] d.h. 1035.382286: sched_stat_runtime: comm=stress pid=10352 runtime=995769 [ns] vruntime=0 [ns]
[vruntime=0 means it is a RT task]
- wait
<idle>-0 [004] dN.. 1227.688544: sched_stat_wait: comm=stress pid=10352 delay=46849882 [ns]
- blocked
kworker/4:1-465 [004] dN.. 1585.676371: sched_stat_blocked: comm=stress pid=17194 delay=189963 [ns]
- iowait
kworker/4:1-465 [004] dN.. 1585.675330: sched_stat_iowait: comm=stress pid=17189 delay=182848 [ns]
- sleep
sleep-18194 [023] dN.. 1780.891840: sched_stat_sleep: comm=sleep.sh pid=17767 delay=1001160770 [ns]
sleep-18196 [023] dN.. 1781.893208: sched_stat_sleep: comm=sleep.sh pid=17767 delay=1001161970 [ns]
sleep-18197 [023] dN.. 1782.894544: sched_stat_sleep: comm=sleep.sh pid=17767 delay=1001128840 [ns]
[ In sleep.sh, it sleeps 1 sec each time. ]
[lkp@intel.com: reported build failure in earlier version]
Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20210905143547.4668-7-laoar.shao@gmail.com
2021-09-05 14:35:45 +00:00
|
|
|
struct sched_rt_entity *rt_se = &p->rt;
|
|
|
|
struct rt_rq *rt_rq = &rq->rt;
|
|
|
|
|
sched/core: Introduce set_next_task() helper for better code readability
When we pick the next task, we will do the following for the task:
1) p->se.exec_start = rq_clock_task(rq);
2) dequeue_pushable(_dl)_task(rq, p);
When we call set_curr_task(), we also need to do the same thing
above. In rt.c, the code at 1) is in the _pick_next_task_rt()
and the code at 2) is in the pick_next_task_rt(). If we put two
operations in one function, maybe better. So, we introduce a new
function set_next_task(), which is responsible for doing the above.
By introducing the function we can get rid of calling the
dequeue_pushable(_dl)_task() directly(We can call set_next_task())
in pick_next_task() and have better code readability and reuse.
In set_curr_task_rt(), we also can call set_next_task().
Do this things such that we end up with:
static struct task_struct *pick_next_task(struct rq *rq,
struct task_struct *prev,
struct rq_flags *rf)
{
/* do something else ... */
put_prev_task(rq, prev);
/* pick next task p */
set_next_task(rq, p);
/* do something else ... */
}
put_prev_task() can match set_next_task(), which can make the
code more readable.
Signed-off-by: Muchun Song <smuchun@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20181026131743.21786-1-smuchun@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-10-26 13:17:43 +00:00
|
|
|
p->se.exec_start = rq_clock_task(rq);
|
sched/rt: Support schedstats for RT sched class
We want to measure the latency of RT tasks in our production
environment with schedstats facility, but currently schedstats is only
supported for fair sched class. This patch enable it for RT sched class
as well.
After we make the struct sched_statistics and the helpers of it
independent of fair sched class, we can easily use the schedstats
facility for RT sched class.
The schedstat usage in RT sched class is similar with fair sched class,
for example,
fair RT
enqueue update_stats_enqueue_fair update_stats_enqueue_rt
dequeue update_stats_dequeue_fair update_stats_dequeue_rt
put_prev_task update_stats_wait_start update_stats_wait_start_rt
set_next_task update_stats_wait_end update_stats_wait_end_rt
The user can get the schedstats information in the same way in fair sched
class. For example,
fair RT
/proc/[pid]/sched /proc/[pid]/sched
schedstats is not supported for RT group.
The output of a RT task's schedstats as follows,
$ cat /proc/10349/sched
...
sum_sleep_runtime : 972.434535
sum_block_runtime : 960.433522
wait_start : 188510.871584
sleep_start : 0.000000
block_start : 0.000000
sleep_max : 12.001013
block_max : 952.660622
exec_max : 0.049629
slice_max : 0.000000
wait_max : 0.018538
wait_sum : 0.424340
wait_count : 49
iowait_sum : 956.495640
iowait_count : 24
nr_migrations_cold : 0
nr_failed_migrations_affine : 0
nr_failed_migrations_running : 0
nr_failed_migrations_hot : 0
nr_forced_migrations : 0
nr_wakeups : 49
nr_wakeups_sync : 0
nr_wakeups_migrate : 0
nr_wakeups_local : 49
nr_wakeups_remote : 0
nr_wakeups_affine : 0
nr_wakeups_affine_attempts : 0
nr_wakeups_passive : 0
nr_wakeups_idle : 0
...
The sched:sched_stat_{wait, sleep, iowait, blocked} tracepoints can
be used to trace RT tasks as well. The output of these tracepoints for a
RT tasks as follows,
- runtime
stress-10352 [004] d.h. 1035.382286: sched_stat_runtime: comm=stress pid=10352 runtime=995769 [ns] vruntime=0 [ns]
[vruntime=0 means it is a RT task]
- wait
<idle>-0 [004] dN.. 1227.688544: sched_stat_wait: comm=stress pid=10352 delay=46849882 [ns]
- blocked
kworker/4:1-465 [004] dN.. 1585.676371: sched_stat_blocked: comm=stress pid=17194 delay=189963 [ns]
- iowait
kworker/4:1-465 [004] dN.. 1585.675330: sched_stat_iowait: comm=stress pid=17189 delay=182848 [ns]
- sleep
sleep-18194 [023] dN.. 1780.891840: sched_stat_sleep: comm=sleep.sh pid=17767 delay=1001160770 [ns]
sleep-18196 [023] dN.. 1781.893208: sched_stat_sleep: comm=sleep.sh pid=17767 delay=1001161970 [ns]
sleep-18197 [023] dN.. 1782.894544: sched_stat_sleep: comm=sleep.sh pid=17767 delay=1001128840 [ns]
[ In sleep.sh, it sleeps 1 sec each time. ]
[lkp@intel.com: reported build failure in earlier version]
Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20210905143547.4668-7-laoar.shao@gmail.com
2021-09-05 14:35:45 +00:00
|
|
|
if (on_rt_rq(&p->rt))
|
|
|
|
update_stats_wait_end_rt(rt_rq, rt_se);
|
sched/core: Introduce set_next_task() helper for better code readability
When we pick the next task, we will do the following for the task:
1) p->se.exec_start = rq_clock_task(rq);
2) dequeue_pushable(_dl)_task(rq, p);
When we call set_curr_task(), we also need to do the same thing
above. In rt.c, the code at 1) is in the _pick_next_task_rt()
and the code at 2) is in the pick_next_task_rt(). If we put two
operations in one function, maybe better. So, we introduce a new
function set_next_task(), which is responsible for doing the above.
By introducing the function we can get rid of calling the
dequeue_pushable(_dl)_task() directly(We can call set_next_task())
in pick_next_task() and have better code readability and reuse.
In set_curr_task_rt(), we also can call set_next_task().
Do this things such that we end up with:
static struct task_struct *pick_next_task(struct rq *rq,
struct task_struct *prev,
struct rq_flags *rf)
{
/* do something else ... */
put_prev_task(rq, prev);
/* pick next task p */
set_next_task(rq, p);
/* do something else ... */
}
put_prev_task() can match set_next_task(), which can make the
code more readable.
Signed-off-by: Muchun Song <smuchun@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20181026131743.21786-1-smuchun@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-10-26 13:17:43 +00:00
|
|
|
|
|
|
|
/* The running task is never eligible for pushing */
|
|
|
|
dequeue_pushable_task(rq, p);
|
2019-05-29 20:36:40 +00:00
|
|
|
|
2019-11-08 13:16:00 +00:00
|
|
|
if (!first)
|
|
|
|
return;
|
|
|
|
|
2019-05-29 20:36:40 +00:00
|
|
|
/*
|
|
|
|
* If prev task was rt, put_prev_task() has already updated the
|
|
|
|
* utilization. We only care of the case where we start to schedule a
|
|
|
|
* rt task
|
|
|
|
*/
|
|
|
|
if (rq->curr->sched_class != &rt_sched_class)
|
|
|
|
update_rt_rq_load_avg(rq_clock_pelt(rq), rq, 0);
|
|
|
|
|
|
|
|
rt_queue_push_tasks(rq);
|
sched/core: Introduce set_next_task() helper for better code readability
When we pick the next task, we will do the following for the task:
1) p->se.exec_start = rq_clock_task(rq);
2) dequeue_pushable(_dl)_task(rq, p);
When we call set_curr_task(), we also need to do the same thing
above. In rt.c, the code at 1) is in the _pick_next_task_rt()
and the code at 2) is in the pick_next_task_rt(). If we put two
operations in one function, maybe better. So, we introduce a new
function set_next_task(), which is responsible for doing the above.
By introducing the function we can get rid of calling the
dequeue_pushable(_dl)_task() directly(We can call set_next_task())
in pick_next_task() and have better code readability and reuse.
In set_curr_task_rt(), we also can call set_next_task().
Do this things such that we end up with:
static struct task_struct *pick_next_task(struct rq *rq,
struct task_struct *prev,
struct rq_flags *rf)
{
/* do something else ... */
put_prev_task(rq, prev);
/* pick next task p */
set_next_task(rq, p);
/* do something else ... */
}
put_prev_task() can match set_next_task(), which can make the
code more readable.
Signed-off-by: Muchun Song <smuchun@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20181026131743.21786-1-smuchun@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-10-26 13:17:43 +00:00
|
|
|
}
|
|
|
|
|
2022-03-02 18:34:33 +00:00
|
|
|
static struct sched_rt_entity *pick_next_rt_entity(struct rt_rq *rt_rq)
|
2007-07-09 16:51:58 +00:00
|
|
|
{
|
2008-01-25 20:08:30 +00:00
|
|
|
struct rt_prio_array *array = &rt_rq->active;
|
|
|
|
struct sched_rt_entity *next = NULL;
|
2007-07-09 16:51:58 +00:00
|
|
|
struct list_head *queue;
|
|
|
|
int idx;
|
|
|
|
|
|
|
|
idx = sched_find_first_bit(array->bitmap);
|
2008-01-25 20:08:30 +00:00
|
|
|
BUG_ON(idx >= MAX_RT_PRIO);
|
2007-07-09 16:51:58 +00:00
|
|
|
|
|
|
|
queue = array->queue + idx;
|
2008-01-25 20:08:30 +00:00
|
|
|
next = list_entry(queue->next, struct sched_rt_entity, run_list);
|
2008-01-25 20:08:34 +00:00
|
|
|
|
2008-01-25 20:08:30 +00:00
|
|
|
return next;
|
|
|
|
}
|
2007-07-09 16:51:58 +00:00
|
|
|
|
sched: create "pushable_tasks" list to limit pushing to one attempt
The RT scheduler employs a "push/pull" design to actively balance tasks
within the system (on a per disjoint cpuset basis). When a task is
awoken, it is immediately determined if there are any lower priority
cpus which should be preempted. This is opposed to the way normal
SCHED_OTHER tasks behave, which will wait for a periodic rebalancing
operation to occur before spreading out load.
When a particular RQ has more than 1 active RT task, it is said to
be in an "overloaded" state. Once this occurs, the system enters
the active balancing mode, where it will try to push the task away,
or persuade a different cpu to pull it over. The system will stay
in this state until the system falls back below the <= 1 queued RT
task per RQ.
However, the current implementation suffers from a limitation in the
push logic. Once overloaded, all tasks (other than current) on the
RQ are analyzed on every push operation, even if it was previously
unpushable (due to affinity, etc). Whats more, the operation stops
at the first task that is unpushable and will not look at items
lower in the queue. This causes two problems:
1) We can have the same tasks analyzed over and over again during each
push, which extends out the fast path in the scheduler for no
gain. Consider a RQ that has dozens of tasks that are bound to a
core. Each one of those tasks will be encountered and skipped
for each push operation while they are queued.
2) There may be lower-priority tasks under the unpushable task that
could have been successfully pushed, but will never be considered
until either the unpushable task is cleared, or a pull operation
succeeds. The net result is a potential latency source for mid
priority tasks.
This patch aims to rectify these two conditions by introducing a new
priority sorted list: "pushable_tasks". A task is added to the list
each time a task is activated or preempted. It is removed from the
list any time it is deactivated, made current, or fails to push.
This works because a task only needs to be attempted to push once.
After an initial failure to push, the other cpus will eventually try to
pull the task when the conditions are proper. This also solves the
problem that we don't completely analyze all tasks due to encountering
an unpushable tasks. Now every task will have a push attempted (when
appropriate).
This reduces latency both by shorting the critical section of the
rq->lock for certain workloads, and by making sure the algorithm
considers all eligible tasks in the system.
[ rostedt: added a couple more BUG_ONs ]
Signed-off-by: Gregory Haskins <ghaskins@novell.com>
Acked-by: Steven Rostedt <srostedt@redhat.com>
2008-12-29 14:39:53 +00:00
|
|
|
static struct task_struct *_pick_next_task_rt(struct rq *rq)
|
2008-01-25 20:08:30 +00:00
|
|
|
{
|
|
|
|
struct sched_rt_entity *rt_se;
|
2012-02-11 05:05:00 +00:00
|
|
|
struct rt_rq *rt_rq = &rq->rt;
|
2008-01-25 20:08:30 +00:00
|
|
|
|
|
|
|
do {
|
2022-03-02 18:34:33 +00:00
|
|
|
rt_se = pick_next_rt_entity(rt_rq);
|
2008-01-25 20:08:34 +00:00
|
|
|
BUG_ON(!rt_se);
|
2008-01-25 20:08:30 +00:00
|
|
|
rt_rq = group_rt_rq(rt_se);
|
|
|
|
} while (rt_rq);
|
|
|
|
|
sched/core: Introduce set_next_task() helper for better code readability
When we pick the next task, we will do the following for the task:
1) p->se.exec_start = rq_clock_task(rq);
2) dequeue_pushable(_dl)_task(rq, p);
When we call set_curr_task(), we also need to do the same thing
above. In rt.c, the code at 1) is in the _pick_next_task_rt()
and the code at 2) is in the pick_next_task_rt(). If we put two
operations in one function, maybe better. So, we introduce a new
function set_next_task(), which is responsible for doing the above.
By introducing the function we can get rid of calling the
dequeue_pushable(_dl)_task() directly(We can call set_next_task())
in pick_next_task() and have better code readability and reuse.
In set_curr_task_rt(), we also can call set_next_task().
Do this things such that we end up with:
static struct task_struct *pick_next_task(struct rq *rq,
struct task_struct *prev,
struct rq_flags *rf)
{
/* do something else ... */
put_prev_task(rq, prev);
/* pick next task p */
set_next_task(rq, p);
/* do something else ... */
}
put_prev_task() can match set_next_task(), which can make the
code more readable.
Signed-off-by: Muchun Song <smuchun@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20181026131743.21786-1-smuchun@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-10-26 13:17:43 +00:00
|
|
|
return rt_task_of(rt_se);
|
sched: create "pushable_tasks" list to limit pushing to one attempt
The RT scheduler employs a "push/pull" design to actively balance tasks
within the system (on a per disjoint cpuset basis). When a task is
awoken, it is immediately determined if there are any lower priority
cpus which should be preempted. This is opposed to the way normal
SCHED_OTHER tasks behave, which will wait for a periodic rebalancing
operation to occur before spreading out load.
When a particular RQ has more than 1 active RT task, it is said to
be in an "overloaded" state. Once this occurs, the system enters
the active balancing mode, where it will try to push the task away,
or persuade a different cpu to pull it over. The system will stay
in this state until the system falls back below the <= 1 queued RT
task per RQ.
However, the current implementation suffers from a limitation in the
push logic. Once overloaded, all tasks (other than current) on the
RQ are analyzed on every push operation, even if it was previously
unpushable (due to affinity, etc). Whats more, the operation stops
at the first task that is unpushable and will not look at items
lower in the queue. This causes two problems:
1) We can have the same tasks analyzed over and over again during each
push, which extends out the fast path in the scheduler for no
gain. Consider a RQ that has dozens of tasks that are bound to a
core. Each one of those tasks will be encountered and skipped
for each push operation while they are queued.
2) There may be lower-priority tasks under the unpushable task that
could have been successfully pushed, but will never be considered
until either the unpushable task is cleared, or a pull operation
succeeds. The net result is a potential latency source for mid
priority tasks.
This patch aims to rectify these two conditions by introducing a new
priority sorted list: "pushable_tasks". A task is added to the list
each time a task is activated or preempted. It is removed from the
list any time it is deactivated, made current, or fails to push.
This works because a task only needs to be attempted to push once.
After an initial failure to push, the other cpus will eventually try to
pull the task when the conditions are proper. This also solves the
problem that we don't completely analyze all tasks due to encountering
an unpushable tasks. Now every task will have a push attempted (when
appropriate).
This reduces latency both by shorting the critical section of the
rq->lock for certain workloads, and by making sure the algorithm
considers all eligible tasks in the system.
[ rostedt: added a couple more BUG_ONs ]
Signed-off-by: Gregory Haskins <ghaskins@novell.com>
Acked-by: Steven Rostedt <srostedt@redhat.com>
2008-12-29 14:39:53 +00:00
|
|
|
}
|
|
|
|
|
2020-11-17 23:19:32 +00:00
|
|
|
static struct task_struct *pick_task_rt(struct rq *rq)
|
sched: create "pushable_tasks" list to limit pushing to one attempt
The RT scheduler employs a "push/pull" design to actively balance tasks
within the system (on a per disjoint cpuset basis). When a task is
awoken, it is immediately determined if there are any lower priority
cpus which should be preempted. This is opposed to the way normal
SCHED_OTHER tasks behave, which will wait for a periodic rebalancing
operation to occur before spreading out load.
When a particular RQ has more than 1 active RT task, it is said to
be in an "overloaded" state. Once this occurs, the system enters
the active balancing mode, where it will try to push the task away,
or persuade a different cpu to pull it over. The system will stay
in this state until the system falls back below the <= 1 queued RT
task per RQ.
However, the current implementation suffers from a limitation in the
push logic. Once overloaded, all tasks (other than current) on the
RQ are analyzed on every push operation, even if it was previously
unpushable (due to affinity, etc). Whats more, the operation stops
at the first task that is unpushable and will not look at items
lower in the queue. This causes two problems:
1) We can have the same tasks analyzed over and over again during each
push, which extends out the fast path in the scheduler for no
gain. Consider a RQ that has dozens of tasks that are bound to a
core. Each one of those tasks will be encountered and skipped
for each push operation while they are queued.
2) There may be lower-priority tasks under the unpushable task that
could have been successfully pushed, but will never be considered
until either the unpushable task is cleared, or a pull operation
succeeds. The net result is a potential latency source for mid
priority tasks.
This patch aims to rectify these two conditions by introducing a new
priority sorted list: "pushable_tasks". A task is added to the list
each time a task is activated or preempted. It is removed from the
list any time it is deactivated, made current, or fails to push.
This works because a task only needs to be attempted to push once.
After an initial failure to push, the other cpus will eventually try to
pull the task when the conditions are proper. This also solves the
problem that we don't completely analyze all tasks due to encountering
an unpushable tasks. Now every task will have a push attempted (when
appropriate).
This reduces latency both by shorting the critical section of the
rq->lock for certain workloads, and by making sure the algorithm
considers all eligible tasks in the system.
[ rostedt: added a couple more BUG_ONs ]
Signed-off-by: Gregory Haskins <ghaskins@novell.com>
Acked-by: Steven Rostedt <srostedt@redhat.com>
2008-12-29 14:39:53 +00:00
|
|
|
{
|
2012-02-11 05:05:00 +00:00
|
|
|
struct task_struct *p;
|
|
|
|
|
2019-11-08 10:11:52 +00:00
|
|
|
if (!sched_rt_runnable(rq))
|
2012-02-11 05:05:00 +00:00
|
|
|
return NULL;
|
|
|
|
|
|
|
|
p = _pick_next_task_rt(rq);
|
2020-11-17 23:19:32 +00:00
|
|
|
|
|
|
|
return p;
|
|
|
|
}
|
|
|
|
|
|
|
|
static struct task_struct *pick_next_task_rt(struct rq *rq)
|
|
|
|
{
|
|
|
|
struct task_struct *p = pick_task_rt(rq);
|
|
|
|
|
|
|
|
if (p)
|
|
|
|
set_next_task_rt(rq, p, true);
|
|
|
|
|
2008-01-25 20:08:30 +00:00
|
|
|
return p;
|
2007-07-09 16:51:58 +00:00
|
|
|
}
|
|
|
|
|
2019-11-08 10:11:52 +00:00
|
|
|
static void put_prev_task_rt(struct rq *rq, struct task_struct *p)
|
2007-07-09 16:51:58 +00:00
|
|
|
{
|
sched/rt: Support schedstats for RT sched class
We want to measure the latency of RT tasks in our production
environment with schedstats facility, but currently schedstats is only
supported for fair sched class. This patch enable it for RT sched class
as well.
After we make the struct sched_statistics and the helpers of it
independent of fair sched class, we can easily use the schedstats
facility for RT sched class.
The schedstat usage in RT sched class is similar with fair sched class,
for example,
fair RT
enqueue update_stats_enqueue_fair update_stats_enqueue_rt
dequeue update_stats_dequeue_fair update_stats_dequeue_rt
put_prev_task update_stats_wait_start update_stats_wait_start_rt
set_next_task update_stats_wait_end update_stats_wait_end_rt
The user can get the schedstats information in the same way in fair sched
class. For example,
fair RT
/proc/[pid]/sched /proc/[pid]/sched
schedstats is not supported for RT group.
The output of a RT task's schedstats as follows,
$ cat /proc/10349/sched
...
sum_sleep_runtime : 972.434535
sum_block_runtime : 960.433522
wait_start : 188510.871584
sleep_start : 0.000000
block_start : 0.000000
sleep_max : 12.001013
block_max : 952.660622
exec_max : 0.049629
slice_max : 0.000000
wait_max : 0.018538
wait_sum : 0.424340
wait_count : 49
iowait_sum : 956.495640
iowait_count : 24
nr_migrations_cold : 0
nr_failed_migrations_affine : 0
nr_failed_migrations_running : 0
nr_failed_migrations_hot : 0
nr_forced_migrations : 0
nr_wakeups : 49
nr_wakeups_sync : 0
nr_wakeups_migrate : 0
nr_wakeups_local : 49
nr_wakeups_remote : 0
nr_wakeups_affine : 0
nr_wakeups_affine_attempts : 0
nr_wakeups_passive : 0
nr_wakeups_idle : 0
...
The sched:sched_stat_{wait, sleep, iowait, blocked} tracepoints can
be used to trace RT tasks as well. The output of these tracepoints for a
RT tasks as follows,
- runtime
stress-10352 [004] d.h. 1035.382286: sched_stat_runtime: comm=stress pid=10352 runtime=995769 [ns] vruntime=0 [ns]
[vruntime=0 means it is a RT task]
- wait
<idle>-0 [004] dN.. 1227.688544: sched_stat_wait: comm=stress pid=10352 delay=46849882 [ns]
- blocked
kworker/4:1-465 [004] dN.. 1585.676371: sched_stat_blocked: comm=stress pid=17194 delay=189963 [ns]
- iowait
kworker/4:1-465 [004] dN.. 1585.675330: sched_stat_iowait: comm=stress pid=17189 delay=182848 [ns]
- sleep
sleep-18194 [023] dN.. 1780.891840: sched_stat_sleep: comm=sleep.sh pid=17767 delay=1001160770 [ns]
sleep-18196 [023] dN.. 1781.893208: sched_stat_sleep: comm=sleep.sh pid=17767 delay=1001161970 [ns]
sleep-18197 [023] dN.. 1782.894544: sched_stat_sleep: comm=sleep.sh pid=17767 delay=1001128840 [ns]
[ In sleep.sh, it sleeps 1 sec each time. ]
[lkp@intel.com: reported build failure in earlier version]
Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20210905143547.4668-7-laoar.shao@gmail.com
2021-09-05 14:35:45 +00:00
|
|
|
struct sched_rt_entity *rt_se = &p->rt;
|
|
|
|
struct rt_rq *rt_rq = &rq->rt;
|
|
|
|
|
|
|
|
if (on_rt_rq(&p->rt))
|
|
|
|
update_stats_wait_start_rt(rt_rq, rt_se);
|
|
|
|
|
2007-08-09 09:16:48 +00:00
|
|
|
update_curr_rt(rq);
|
sched: create "pushable_tasks" list to limit pushing to one attempt
The RT scheduler employs a "push/pull" design to actively balance tasks
within the system (on a per disjoint cpuset basis). When a task is
awoken, it is immediately determined if there are any lower priority
cpus which should be preempted. This is opposed to the way normal
SCHED_OTHER tasks behave, which will wait for a periodic rebalancing
operation to occur before spreading out load.
When a particular RQ has more than 1 active RT task, it is said to
be in an "overloaded" state. Once this occurs, the system enters
the active balancing mode, where it will try to push the task away,
or persuade a different cpu to pull it over. The system will stay
in this state until the system falls back below the <= 1 queued RT
task per RQ.
However, the current implementation suffers from a limitation in the
push logic. Once overloaded, all tasks (other than current) on the
RQ are analyzed on every push operation, even if it was previously
unpushable (due to affinity, etc). Whats more, the operation stops
at the first task that is unpushable and will not look at items
lower in the queue. This causes two problems:
1) We can have the same tasks analyzed over and over again during each
push, which extends out the fast path in the scheduler for no
gain. Consider a RQ that has dozens of tasks that are bound to a
core. Each one of those tasks will be encountered and skipped
for each push operation while they are queued.
2) There may be lower-priority tasks under the unpushable task that
could have been successfully pushed, but will never be considered
until either the unpushable task is cleared, or a pull operation
succeeds. The net result is a potential latency source for mid
priority tasks.
This patch aims to rectify these two conditions by introducing a new
priority sorted list: "pushable_tasks". A task is added to the list
each time a task is activated or preempted. It is removed from the
list any time it is deactivated, made current, or fails to push.
This works because a task only needs to be attempted to push once.
After an initial failure to push, the other cpus will eventually try to
pull the task when the conditions are proper. This also solves the
problem that we don't completely analyze all tasks due to encountering
an unpushable tasks. Now every task will have a push attempted (when
appropriate).
This reduces latency both by shorting the critical section of the
rq->lock for certain workloads, and by making sure the algorithm
considers all eligible tasks in the system.
[ rostedt: added a couple more BUG_ONs ]
Signed-off-by: Gregory Haskins <ghaskins@novell.com>
Acked-by: Steven Rostedt <srostedt@redhat.com>
2008-12-29 14:39:53 +00:00
|
|
|
|
sched/fair: Update scale invariance of PELT
The current implementation of load tracking invariance scales the
contribution with current frequency and uarch performance (only for
utilization) of the CPU. One main result of this formula is that the
figures are capped by current capacity of CPU. Another one is that the
load_avg is not invariant because not scaled with uarch.
The util_avg of a periodic task that runs r time slots every p time slots
varies in the range :
U * (1-y^r)/(1-y^p) * y^i < Utilization < U * (1-y^r)/(1-y^p)
with U is the max util_avg value = SCHED_CAPACITY_SCALE
At a lower capacity, the range becomes:
U * C * (1-y^r')/(1-y^p) * y^i' < Utilization < U * C * (1-y^r')/(1-y^p)
with C reflecting the compute capacity ratio between current capacity and
max capacity.
so C tries to compensate changes in (1-y^r') but it can't be accurate.
Instead of scaling the contribution value of PELT algo, we should scale the
running time. The PELT signal aims to track the amount of computation of
tasks and/or rq so it seems more correct to scale the running time to
reflect the effective amount of computation done since the last update.
In order to be fully invariant, we need to apply the same amount of
running time and idle time whatever the current capacity. Because running
at lower capacity implies that the task will run longer, we have to ensure
that the same amount of idle time will be applied when system becomes idle
and no idle time has been "stolen". But reaching the maximum utilization
value (SCHED_CAPACITY_SCALE) means that the task is seen as an
always-running task whatever the capacity of the CPU (even at max compute
capacity). In this case, we can discard this "stolen" idle times which
becomes meaningless.
In order to achieve this time scaling, a new clock_pelt is created per rq.
The increase of this clock scales with current capacity when something
is running on rq and synchronizes with clock_task when rq is idle. With
this mechanism, we ensure the same running and idle time whatever the
current capacity. This also enables to simplify the pelt algorithm by
removing all references of uarch and frequency and applying the same
contribution to utilization and loads. Furthermore, the scaling is done
only once per update of clock (update_rq_clock_task()) instead of during
each update of sched_entities and cfs/rt/dl_rq of the rq like the current
implementation. This is interesting when cgroup are involved as shown in
the results below:
On a hikey (octo Arm64 platform).
Performance cpufreq governor and only shallowest c-state to remove variance
generated by those power features so we only track the impact of pelt algo.
each test runs 16 times:
./perf bench sched pipe
(higher is better)
kernel tip/sched/core + patch
ops/seconds ops/seconds diff
cgroup
root 59652(+/- 0.18%) 59876(+/- 0.24%) +0.38%
level1 55608(+/- 0.27%) 55923(+/- 0.24%) +0.57%
level2 52115(+/- 0.29%) 52564(+/- 0.22%) +0.86%
hackbench -l 1000
(lower is better)
kernel tip/sched/core + patch
duration(sec) duration(sec) diff
cgroup
root 4.453(+/- 2.37%) 4.383(+/- 2.88%) -1.57%
level1 4.859(+/- 8.50%) 4.830(+/- 7.07%) -0.60%
level2 5.063(+/- 9.83%) 4.928(+/- 9.66%) -2.66%
Then, the responsiveness of PELT is improved when CPU is not running at max
capacity with this new algorithm. I have put below some examples of
duration to reach some typical load values according to the capacity of the
CPU with current implementation and with this patch. These values has been
computed based on the geometric series and the half period value:
Util (%) max capacity half capacity(mainline) half capacity(w/ patch)
972 (95%) 138ms not reachable 276ms
486 (47.5%) 30ms 138ms 60ms
256 (25%) 13ms 32ms 26ms
On my hikey (octo Arm64 platform) with schedutil governor, the time to
reach max OPP when starting from a null utilization, decreases from 223ms
with current scale invariance down to 121ms with the new algorithm.
Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Morten.Rasmussen@arm.com
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: bsegall@google.com
Cc: dietmar.eggemann@arm.com
Cc: patrick.bellasi@arm.com
Cc: pjt@google.com
Cc: pkondeti@codeaurora.org
Cc: quentin.perret@arm.com
Cc: rjw@rjwysocki.net
Cc: srinivas.pandruvada@linux.intel.com
Cc: thara.gopinath@linaro.org
Link: https://lkml.kernel.org/r/1548257214-13745-3-git-send-email-vincent.guittot@linaro.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2019-01-23 15:26:53 +00:00
|
|
|
update_rt_rq_load_avg(rq_clock_pelt(rq), rq, 1);
|
2018-06-28 15:45:05 +00:00
|
|
|
|
sched: create "pushable_tasks" list to limit pushing to one attempt
The RT scheduler employs a "push/pull" design to actively balance tasks
within the system (on a per disjoint cpuset basis). When a task is
awoken, it is immediately determined if there are any lower priority
cpus which should be preempted. This is opposed to the way normal
SCHED_OTHER tasks behave, which will wait for a periodic rebalancing
operation to occur before spreading out load.
When a particular RQ has more than 1 active RT task, it is said to
be in an "overloaded" state. Once this occurs, the system enters
the active balancing mode, where it will try to push the task away,
or persuade a different cpu to pull it over. The system will stay
in this state until the system falls back below the <= 1 queued RT
task per RQ.
However, the current implementation suffers from a limitation in the
push logic. Once overloaded, all tasks (other than current) on the
RQ are analyzed on every push operation, even if it was previously
unpushable (due to affinity, etc). Whats more, the operation stops
at the first task that is unpushable and will not look at items
lower in the queue. This causes two problems:
1) We can have the same tasks analyzed over and over again during each
push, which extends out the fast path in the scheduler for no
gain. Consider a RQ that has dozens of tasks that are bound to a
core. Each one of those tasks will be encountered and skipped
for each push operation while they are queued.
2) There may be lower-priority tasks under the unpushable task that
could have been successfully pushed, but will never be considered
until either the unpushable task is cleared, or a pull operation
succeeds. The net result is a potential latency source for mid
priority tasks.
This patch aims to rectify these two conditions by introducing a new
priority sorted list: "pushable_tasks". A task is added to the list
each time a task is activated or preempted. It is removed from the
list any time it is deactivated, made current, or fails to push.
This works because a task only needs to be attempted to push once.
After an initial failure to push, the other cpus will eventually try to
pull the task when the conditions are proper. This also solves the
problem that we don't completely analyze all tasks due to encountering
an unpushable tasks. Now every task will have a push attempted (when
appropriate).
This reduces latency both by shorting the critical section of the
rq->lock for certain workloads, and by making sure the algorithm
considers all eligible tasks in the system.
[ rostedt: added a couple more BUG_ONs ]
Signed-off-by: Gregory Haskins <ghaskins@novell.com>
Acked-by: Steven Rostedt <srostedt@redhat.com>
2008-12-29 14:39:53 +00:00
|
|
|
/*
|
|
|
|
* The previous task needs to be made eligible for pushing
|
|
|
|
* if it is still active
|
|
|
|
*/
|
2017-02-05 14:41:03 +00:00
|
|
|
if (on_rt_rq(&p->rt) && p->nr_cpus_allowed > 1)
|
sched: create "pushable_tasks" list to limit pushing to one attempt
The RT scheduler employs a "push/pull" design to actively balance tasks
within the system (on a per disjoint cpuset basis). When a task is
awoken, it is immediately determined if there are any lower priority
cpus which should be preempted. This is opposed to the way normal
SCHED_OTHER tasks behave, which will wait for a periodic rebalancing
operation to occur before spreading out load.
When a particular RQ has more than 1 active RT task, it is said to
be in an "overloaded" state. Once this occurs, the system enters
the active balancing mode, where it will try to push the task away,
or persuade a different cpu to pull it over. The system will stay
in this state until the system falls back below the <= 1 queued RT
task per RQ.
However, the current implementation suffers from a limitation in the
push logic. Once overloaded, all tasks (other than current) on the
RQ are analyzed on every push operation, even if it was previously
unpushable (due to affinity, etc). Whats more, the operation stops
at the first task that is unpushable and will not look at items
lower in the queue. This causes two problems:
1) We can have the same tasks analyzed over and over again during each
push, which extends out the fast path in the scheduler for no
gain. Consider a RQ that has dozens of tasks that are bound to a
core. Each one of those tasks will be encountered and skipped
for each push operation while they are queued.
2) There may be lower-priority tasks under the unpushable task that
could have been successfully pushed, but will never be considered
until either the unpushable task is cleared, or a pull operation
succeeds. The net result is a potential latency source for mid
priority tasks.
This patch aims to rectify these two conditions by introducing a new
priority sorted list: "pushable_tasks". A task is added to the list
each time a task is activated or preempted. It is removed from the
list any time it is deactivated, made current, or fails to push.
This works because a task only needs to be attempted to push once.
After an initial failure to push, the other cpus will eventually try to
pull the task when the conditions are proper. This also solves the
problem that we don't completely analyze all tasks due to encountering
an unpushable tasks. Now every task will have a push attempted (when
appropriate).
This reduces latency both by shorting the critical section of the
rq->lock for certain workloads, and by making sure the algorithm
considers all eligible tasks in the system.
[ rostedt: added a couple more BUG_ONs ]
Signed-off-by: Gregory Haskins <ghaskins@novell.com>
Acked-by: Steven Rostedt <srostedt@redhat.com>
2008-12-29 14:39:53 +00:00
|
|
|
enqueue_pushable_task(rq, p);
|
2007-07-09 16:51:58 +00:00
|
|
|
}
|
|
|
|
|
2007-10-24 16:23:51 +00:00
|
|
|
#ifdef CONFIG_SMP
|
2008-01-25 20:08:30 +00:00
|
|
|
|
2008-01-25 20:08:05 +00:00
|
|
|
/* Only try algorithms three times */
|
|
|
|
#define RT_MAX_TRIES 3
|
|
|
|
|
2008-01-25 20:08:07 +00:00
|
|
|
static int pick_rt_task(struct rq *rq, struct task_struct *p, int cpu)
|
|
|
|
{
|
2022-09-06 10:33:04 +00:00
|
|
|
if (!task_on_cpu(rq, p) &&
|
2020-10-01 14:05:39 +00:00
|
|
|
cpumask_test_cpu(cpu, &p->cpus_mask))
|
2008-01-25 20:08:07 +00:00
|
|
|
return 1;
|
sched: Clean up and harmonize the coding style of the scheduler code base
A good number of small style inconsistencies have accumulated
in the scheduler core, so do a pass over them to harmonize
all these details:
- fix speling in comments,
- use curly braces for multi-line statements,
- remove unnecessary parentheses from integer literals,
- capitalize consistently,
- remove stray newlines,
- add comments where necessary,
- remove invalid/unnecessary comments,
- align structure definitions and other data types vertically,
- add missing newlines for increased readability,
- fix vertical tabulation where it's misaligned,
- harmonize preprocessor conditional block labeling
and vertical alignment,
- remove line-breaks where they uglify the code,
- add newline after local variable definitions,
No change in functionality:
md5:
1191fa0a890cfa8132156d2959d7e9e2 built-in.o.before.asm
1191fa0a890cfa8132156d2959d7e9e2 built-in.o.after.asm
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-03-03 13:01:12 +00:00
|
|
|
|
2008-01-25 20:08:07 +00:00
|
|
|
return 0;
|
|
|
|
}
|
|
|
|
|
2013-06-07 19:37:43 +00:00
|
|
|
/*
|
|
|
|
* Return the highest pushable rq's task, which is suitable to be executed
|
sched: Clean up and harmonize the coding style of the scheduler code base
A good number of small style inconsistencies have accumulated
in the scheduler core, so do a pass over them to harmonize
all these details:
- fix speling in comments,
- use curly braces for multi-line statements,
- remove unnecessary parentheses from integer literals,
- capitalize consistently,
- remove stray newlines,
- add comments where necessary,
- remove invalid/unnecessary comments,
- align structure definitions and other data types vertically,
- add missing newlines for increased readability,
- fix vertical tabulation where it's misaligned,
- harmonize preprocessor conditional block labeling
and vertical alignment,
- remove line-breaks where they uglify the code,
- add newline after local variable definitions,
No change in functionality:
md5:
1191fa0a890cfa8132156d2959d7e9e2 built-in.o.before.asm
1191fa0a890cfa8132156d2959d7e9e2 built-in.o.after.asm
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-03-03 13:01:12 +00:00
|
|
|
* on the CPU, NULL otherwise
|
2013-06-07 19:37:43 +00:00
|
|
|
*/
|
|
|
|
static struct task_struct *pick_highest_pushable_task(struct rq *rq, int cpu)
|
2008-01-25 20:08:05 +00:00
|
|
|
{
|
2013-06-07 19:37:43 +00:00
|
|
|
struct plist_head *head = &rq->rt.pushable_tasks;
|
|
|
|
struct task_struct *p;
|
2010-03-10 16:07:24 +00:00
|
|
|
|
2013-06-07 19:37:43 +00:00
|
|
|
if (!has_pushable_tasks(rq))
|
|
|
|
return NULL;
|
2010-03-10 16:07:24 +00:00
|
|
|
|
2013-06-07 19:37:43 +00:00
|
|
|
plist_for_each_entry(p, head, pushable_tasks) {
|
|
|
|
if (pick_rt_task(rq, p, cpu))
|
|
|
|
return p;
|
2008-01-25 20:08:07 +00:00
|
|
|
}
|
|
|
|
|
2013-06-07 19:37:43 +00:00
|
|
|
return NULL;
|
2008-01-25 20:08:05 +00:00
|
|
|
}
|
|
|
|
|
2008-11-24 16:05:13 +00:00
|
|
|
static DEFINE_PER_CPU(cpumask_var_t, local_cpu_mask);
|
2008-01-25 20:08:05 +00:00
|
|
|
|
2008-01-25 20:08:11 +00:00
|
|
|
static int find_lowest_rq(struct task_struct *task)
|
|
|
|
{
|
|
|
|
struct sched_domain *sd;
|
2014-08-27 00:12:21 +00:00
|
|
|
struct cpumask *lowest_mask = this_cpu_cpumask_var_ptr(local_cpu_mask);
|
2008-01-25 20:08:11 +00:00
|
|
|
int this_cpu = smp_processor_id();
|
|
|
|
int cpu = task_cpu(task);
|
2020-03-02 13:27:18 +00:00
|
|
|
int ret;
|
2008-01-25 20:08:13 +00:00
|
|
|
|
2011-06-14 22:36:25 +00:00
|
|
|
/* Make sure the mask is initialized first */
|
|
|
|
if (unlikely(!lowest_mask))
|
|
|
|
return -1;
|
|
|
|
|
2017-02-05 14:41:03 +00:00
|
|
|
if (task->nr_cpus_allowed == 1)
|
2008-05-12 19:21:01 +00:00
|
|
|
return -1; /* No other targets possible */
|
2008-01-25 20:08:11 +00:00
|
|
|
|
2020-03-02 13:27:18 +00:00
|
|
|
/*
|
|
|
|
* If we're on asym system ensure we consider the different capacities
|
|
|
|
* of the CPUs when searching for the lowest_mask.
|
|
|
|
*/
|
2022-07-29 11:13:03 +00:00
|
|
|
if (sched_asym_cpucap_active()) {
|
2020-03-02 13:27:18 +00:00
|
|
|
|
|
|
|
ret = cpupri_find_fitness(&task_rq(task)->rd->cpupri,
|
|
|
|
task, lowest_mask,
|
|
|
|
rt_task_fits_capacity);
|
|
|
|
} else {
|
|
|
|
|
|
|
|
ret = cpupri_find(&task_rq(task)->rd->cpupri,
|
|
|
|
task, lowest_mask);
|
|
|
|
}
|
|
|
|
|
|
|
|
if (!ret)
|
2008-05-12 19:21:01 +00:00
|
|
|
return -1; /* No targets found */
|
2008-01-25 20:08:11 +00:00
|
|
|
|
|
|
|
/*
|
sched: Clean up and harmonize the coding style of the scheduler code base
A good number of small style inconsistencies have accumulated
in the scheduler core, so do a pass over them to harmonize
all these details:
- fix speling in comments,
- use curly braces for multi-line statements,
- remove unnecessary parentheses from integer literals,
- capitalize consistently,
- remove stray newlines,
- add comments where necessary,
- remove invalid/unnecessary comments,
- align structure definitions and other data types vertically,
- add missing newlines for increased readability,
- fix vertical tabulation where it's misaligned,
- harmonize preprocessor conditional block labeling
and vertical alignment,
- remove line-breaks where they uglify the code,
- add newline after local variable definitions,
No change in functionality:
md5:
1191fa0a890cfa8132156d2959d7e9e2 built-in.o.before.asm
1191fa0a890cfa8132156d2959d7e9e2 built-in.o.after.asm
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-03-03 13:01:12 +00:00
|
|
|
* At this point we have built a mask of CPUs representing the
|
2008-01-25 20:08:11 +00:00
|
|
|
* lowest priority tasks in the system. Now we want to elect
|
|
|
|
* the best one based on our affinity and topology.
|
|
|
|
*
|
sched: Clean up and harmonize the coding style of the scheduler code base
A good number of small style inconsistencies have accumulated
in the scheduler core, so do a pass over them to harmonize
all these details:
- fix speling in comments,
- use curly braces for multi-line statements,
- remove unnecessary parentheses from integer literals,
- capitalize consistently,
- remove stray newlines,
- add comments where necessary,
- remove invalid/unnecessary comments,
- align structure definitions and other data types vertically,
- add missing newlines for increased readability,
- fix vertical tabulation where it's misaligned,
- harmonize preprocessor conditional block labeling
and vertical alignment,
- remove line-breaks where they uglify the code,
- add newline after local variable definitions,
No change in functionality:
md5:
1191fa0a890cfa8132156d2959d7e9e2 built-in.o.before.asm
1191fa0a890cfa8132156d2959d7e9e2 built-in.o.after.asm
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-03-03 13:01:12 +00:00
|
|
|
* We prioritize the last CPU that the task executed on since
|
2008-01-25 20:08:11 +00:00
|
|
|
* it is most likely cache-hot in that location.
|
|
|
|
*/
|
2008-11-24 16:05:14 +00:00
|
|
|
if (cpumask_test_cpu(cpu, lowest_mask))
|
2008-01-25 20:08:11 +00:00
|
|
|
return cpu;
|
|
|
|
|
|
|
|
/*
|
|
|
|
* Otherwise, we consult the sched_domains span maps to figure
|
sched: Clean up and harmonize the coding style of the scheduler code base
A good number of small style inconsistencies have accumulated
in the scheduler core, so do a pass over them to harmonize
all these details:
- fix speling in comments,
- use curly braces for multi-line statements,
- remove unnecessary parentheses from integer literals,
- capitalize consistently,
- remove stray newlines,
- add comments where necessary,
- remove invalid/unnecessary comments,
- align structure definitions and other data types vertically,
- add missing newlines for increased readability,
- fix vertical tabulation where it's misaligned,
- harmonize preprocessor conditional block labeling
and vertical alignment,
- remove line-breaks where they uglify the code,
- add newline after local variable definitions,
No change in functionality:
md5:
1191fa0a890cfa8132156d2959d7e9e2 built-in.o.before.asm
1191fa0a890cfa8132156d2959d7e9e2 built-in.o.after.asm
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-03-03 13:01:12 +00:00
|
|
|
* out which CPU is logically closest to our hot cache data.
|
2008-01-25 20:08:11 +00:00
|
|
|
*/
|
2009-11-03 04:23:15 +00:00
|
|
|
if (!cpumask_test_cpu(this_cpu, lowest_mask))
|
|
|
|
this_cpu = -1; /* Skip this_cpu opt if not among lowest */
|
2008-01-25 20:08:11 +00:00
|
|
|
|
2011-04-22 10:53:54 +00:00
|
|
|
rcu_read_lock();
|
2009-11-03 04:23:15 +00:00
|
|
|
for_each_domain(cpu, sd) {
|
|
|
|
if (sd->flags & SD_WAKE_AFFINE) {
|
|
|
|
int best_cpu;
|
2008-01-25 20:08:11 +00:00
|
|
|
|
2009-11-03 04:23:15 +00:00
|
|
|
/*
|
|
|
|
* "this_cpu" is cheaper to preempt than a
|
|
|
|
* remote processor.
|
|
|
|
*/
|
|
|
|
if (this_cpu != -1 &&
|
2011-04-22 10:53:54 +00:00
|
|
|
cpumask_test_cpu(this_cpu, sched_domain_span(sd))) {
|
|
|
|
rcu_read_unlock();
|
2009-11-03 04:23:15 +00:00
|
|
|
return this_cpu;
|
2011-04-22 10:53:54 +00:00
|
|
|
}
|
2009-11-03 04:23:15 +00:00
|
|
|
|
2020-10-01 13:54:14 +00:00
|
|
|
best_cpu = cpumask_any_and_distribute(lowest_mask,
|
|
|
|
sched_domain_span(sd));
|
2011-04-22 10:53:54 +00:00
|
|
|
if (best_cpu < nr_cpu_ids) {
|
|
|
|
rcu_read_unlock();
|
2009-11-03 04:23:15 +00:00
|
|
|
return best_cpu;
|
2011-04-22 10:53:54 +00:00
|
|
|
}
|
2008-01-25 20:08:11 +00:00
|
|
|
}
|
|
|
|
}
|
2011-04-22 10:53:54 +00:00
|
|
|
rcu_read_unlock();
|
2008-01-25 20:08:11 +00:00
|
|
|
|
|
|
|
/*
|
|
|
|
* And finally, if there were no matches within the domains
|
|
|
|
* just give the caller *something* to work with from the compatible
|
|
|
|
* locations.
|
|
|
|
*/
|
2009-11-03 04:23:15 +00:00
|
|
|
if (this_cpu != -1)
|
|
|
|
return this_cpu;
|
|
|
|
|
2020-10-01 13:54:14 +00:00
|
|
|
cpu = cpumask_any_distribute(lowest_mask);
|
2009-11-03 04:23:15 +00:00
|
|
|
if (cpu < nr_cpu_ids)
|
|
|
|
return cpu;
|
sched: Clean up and harmonize the coding style of the scheduler code base
A good number of small style inconsistencies have accumulated
in the scheduler core, so do a pass over them to harmonize
all these details:
- fix speling in comments,
- use curly braces for multi-line statements,
- remove unnecessary parentheses from integer literals,
- capitalize consistently,
- remove stray newlines,
- add comments where necessary,
- remove invalid/unnecessary comments,
- align structure definitions and other data types vertically,
- add missing newlines for increased readability,
- fix vertical tabulation where it's misaligned,
- harmonize preprocessor conditional block labeling
and vertical alignment,
- remove line-breaks where they uglify the code,
- add newline after local variable definitions,
No change in functionality:
md5:
1191fa0a890cfa8132156d2959d7e9e2 built-in.o.before.asm
1191fa0a890cfa8132156d2959d7e9e2 built-in.o.after.asm
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-03-03 13:01:12 +00:00
|
|
|
|
2009-11-03 04:23:15 +00:00
|
|
|
return -1;
|
2008-01-25 20:08:10 +00:00
|
|
|
}
|
|
|
|
|
|
|
|
/* Will lock the rq it finds */
|
2008-01-25 20:08:15 +00:00
|
|
|
static struct rq *find_lock_lowest_rq(struct task_struct *task, struct rq *rq)
|
2008-01-25 20:08:10 +00:00
|
|
|
{
|
|
|
|
struct rq *lowest_rq = NULL;
|
|
|
|
int tries;
|
2008-01-25 20:08:15 +00:00
|
|
|
int cpu;
|
2008-01-25 20:08:05 +00:00
|
|
|
|
2008-01-25 20:08:10 +00:00
|
|
|
for (tries = 0; tries < RT_MAX_TRIES; tries++) {
|
|
|
|
cpu = find_lowest_rq(task);
|
|
|
|
|
2008-01-25 20:08:10 +00:00
|
|
|
if ((cpu == -1) || (cpu == rq->cpu))
|
2008-01-25 20:08:05 +00:00
|
|
|
break;
|
|
|
|
|
2008-01-25 20:08:10 +00:00
|
|
|
lowest_rq = cpu_rq(cpu);
|
|
|
|
|
2014-12-12 23:38:12 +00:00
|
|
|
if (lowest_rq->rt.highest_prio.curr <= task->prio) {
|
|
|
|
/*
|
|
|
|
* Target rq has tasks of equal or higher priority,
|
|
|
|
* retrying does not release any lock and is unlikely
|
|
|
|
* to yield a different result.
|
|
|
|
*/
|
|
|
|
lowest_rq = NULL;
|
|
|
|
break;
|
|
|
|
}
|
|
|
|
|
2008-01-25 20:08:05 +00:00
|
|
|
/* if the prio of this runqueue changed, try again */
|
2008-01-25 20:08:10 +00:00
|
|
|
if (double_lock_balance(rq, lowest_rq)) {
|
2008-01-25 20:08:05 +00:00
|
|
|
/*
|
|
|
|
* We had to unlock the run queue. In
|
|
|
|
* the mean time, task could have
|
|
|
|
* migrated already or had its affinity changed.
|
|
|
|
* Also make sure that it wasn't scheduled on its rq.
|
|
|
|
*/
|
2008-01-25 20:08:10 +00:00
|
|
|
if (unlikely(task_rq(task) != rq ||
|
2020-10-01 14:05:39 +00:00
|
|
|
!cpumask_test_cpu(lowest_rq->cpu, &task->cpus_mask) ||
|
2022-09-06 10:33:04 +00:00
|
|
|
task_on_cpu(rq, task) ||
|
2016-05-09 04:11:31 +00:00
|
|
|
!rt_task(task) ||
|
2014-08-20 09:47:32 +00:00
|
|
|
!task_on_rq_queued(task))) {
|
2008-01-25 20:08:15 +00:00
|
|
|
|
2012-05-17 19:19:46 +00:00
|
|
|
double_unlock_balance(rq, lowest_rq);
|
2008-01-25 20:08:05 +00:00
|
|
|
lowest_rq = NULL;
|
|
|
|
break;
|
|
|
|
}
|
|
|
|
}
|
|
|
|
|
|
|
|
/* If this rq is still suitable use it. */
|
2008-12-29 14:39:49 +00:00
|
|
|
if (lowest_rq->rt.highest_prio.curr > task->prio)
|
2008-01-25 20:08:05 +00:00
|
|
|
break;
|
|
|
|
|
|
|
|
/* try again */
|
2008-08-11 07:30:22 +00:00
|
|
|
double_unlock_balance(rq, lowest_rq);
|
2008-01-25 20:08:05 +00:00
|
|
|
lowest_rq = NULL;
|
|
|
|
}
|
|
|
|
|
|
|
|
return lowest_rq;
|
|
|
|
}
|
|
|
|
|
sched: create "pushable_tasks" list to limit pushing to one attempt
The RT scheduler employs a "push/pull" design to actively balance tasks
within the system (on a per disjoint cpuset basis). When a task is
awoken, it is immediately determined if there are any lower priority
cpus which should be preempted. This is opposed to the way normal
SCHED_OTHER tasks behave, which will wait for a periodic rebalancing
operation to occur before spreading out load.
When a particular RQ has more than 1 active RT task, it is said to
be in an "overloaded" state. Once this occurs, the system enters
the active balancing mode, where it will try to push the task away,
or persuade a different cpu to pull it over. The system will stay
in this state until the system falls back below the <= 1 queued RT
task per RQ.
However, the current implementation suffers from a limitation in the
push logic. Once overloaded, all tasks (other than current) on the
RQ are analyzed on every push operation, even if it was previously
unpushable (due to affinity, etc). Whats more, the operation stops
at the first task that is unpushable and will not look at items
lower in the queue. This causes two problems:
1) We can have the same tasks analyzed over and over again during each
push, which extends out the fast path in the scheduler for no
gain. Consider a RQ that has dozens of tasks that are bound to a
core. Each one of those tasks will be encountered and skipped
for each push operation while they are queued.
2) There may be lower-priority tasks under the unpushable task that
could have been successfully pushed, but will never be considered
until either the unpushable task is cleared, or a pull operation
succeeds. The net result is a potential latency source for mid
priority tasks.
This patch aims to rectify these two conditions by introducing a new
priority sorted list: "pushable_tasks". A task is added to the list
each time a task is activated or preempted. It is removed from the
list any time it is deactivated, made current, or fails to push.
This works because a task only needs to be attempted to push once.
After an initial failure to push, the other cpus will eventually try to
pull the task when the conditions are proper. This also solves the
problem that we don't completely analyze all tasks due to encountering
an unpushable tasks. Now every task will have a push attempted (when
appropriate).
This reduces latency both by shorting the critical section of the
rq->lock for certain workloads, and by making sure the algorithm
considers all eligible tasks in the system.
[ rostedt: added a couple more BUG_ONs ]
Signed-off-by: Gregory Haskins <ghaskins@novell.com>
Acked-by: Steven Rostedt <srostedt@redhat.com>
2008-12-29 14:39:53 +00:00
|
|
|
static struct task_struct *pick_next_pushable_task(struct rq *rq)
|
|
|
|
{
|
|
|
|
struct task_struct *p;
|
|
|
|
|
|
|
|
if (!has_pushable_tasks(rq))
|
|
|
|
return NULL;
|
|
|
|
|
|
|
|
p = plist_first_entry(&rq->rt.pushable_tasks,
|
|
|
|
struct task_struct, pushable_tasks);
|
|
|
|
|
|
|
|
BUG_ON(rq->cpu != task_cpu(p));
|
|
|
|
BUG_ON(task_current(rq, p));
|
2017-02-05 14:41:03 +00:00
|
|
|
BUG_ON(p->nr_cpus_allowed <= 1);
|
sched: create "pushable_tasks" list to limit pushing to one attempt
The RT scheduler employs a "push/pull" design to actively balance tasks
within the system (on a per disjoint cpuset basis). When a task is
awoken, it is immediately determined if there are any lower priority
cpus which should be preempted. This is opposed to the way normal
SCHED_OTHER tasks behave, which will wait for a periodic rebalancing
operation to occur before spreading out load.
When a particular RQ has more than 1 active RT task, it is said to
be in an "overloaded" state. Once this occurs, the system enters
the active balancing mode, where it will try to push the task away,
or persuade a different cpu to pull it over. The system will stay
in this state until the system falls back below the <= 1 queued RT
task per RQ.
However, the current implementation suffers from a limitation in the
push logic. Once overloaded, all tasks (other than current) on the
RQ are analyzed on every push operation, even if it was previously
unpushable (due to affinity, etc). Whats more, the operation stops
at the first task that is unpushable and will not look at items
lower in the queue. This causes two problems:
1) We can have the same tasks analyzed over and over again during each
push, which extends out the fast path in the scheduler for no
gain. Consider a RQ that has dozens of tasks that are bound to a
core. Each one of those tasks will be encountered and skipped
for each push operation while they are queued.
2) There may be lower-priority tasks under the unpushable task that
could have been successfully pushed, but will never be considered
until either the unpushable task is cleared, or a pull operation
succeeds. The net result is a potential latency source for mid
priority tasks.
This patch aims to rectify these two conditions by introducing a new
priority sorted list: "pushable_tasks". A task is added to the list
each time a task is activated or preempted. It is removed from the
list any time it is deactivated, made current, or fails to push.
This works because a task only needs to be attempted to push once.
After an initial failure to push, the other cpus will eventually try to
pull the task when the conditions are proper. This also solves the
problem that we don't completely analyze all tasks due to encountering
an unpushable tasks. Now every task will have a push attempted (when
appropriate).
This reduces latency both by shorting the critical section of the
rq->lock for certain workloads, and by making sure the algorithm
considers all eligible tasks in the system.
[ rostedt: added a couple more BUG_ONs ]
Signed-off-by: Gregory Haskins <ghaskins@novell.com>
Acked-by: Steven Rostedt <srostedt@redhat.com>
2008-12-29 14:39:53 +00:00
|
|
|
|
2014-08-20 09:47:32 +00:00
|
|
|
BUG_ON(!task_on_rq_queued(p));
|
sched: create "pushable_tasks" list to limit pushing to one attempt
The RT scheduler employs a "push/pull" design to actively balance tasks
within the system (on a per disjoint cpuset basis). When a task is
awoken, it is immediately determined if there are any lower priority
cpus which should be preempted. This is opposed to the way normal
SCHED_OTHER tasks behave, which will wait for a periodic rebalancing
operation to occur before spreading out load.
When a particular RQ has more than 1 active RT task, it is said to
be in an "overloaded" state. Once this occurs, the system enters
the active balancing mode, where it will try to push the task away,
or persuade a different cpu to pull it over. The system will stay
in this state until the system falls back below the <= 1 queued RT
task per RQ.
However, the current implementation suffers from a limitation in the
push logic. Once overloaded, all tasks (other than current) on the
RQ are analyzed on every push operation, even if it was previously
unpushable (due to affinity, etc). Whats more, the operation stops
at the first task that is unpushable and will not look at items
lower in the queue. This causes two problems:
1) We can have the same tasks analyzed over and over again during each
push, which extends out the fast path in the scheduler for no
gain. Consider a RQ that has dozens of tasks that are bound to a
core. Each one of those tasks will be encountered and skipped
for each push operation while they are queued.
2) There may be lower-priority tasks under the unpushable task that
could have been successfully pushed, but will never be considered
until either the unpushable task is cleared, or a pull operation
succeeds. The net result is a potential latency source for mid
priority tasks.
This patch aims to rectify these two conditions by introducing a new
priority sorted list: "pushable_tasks". A task is added to the list
each time a task is activated or preempted. It is removed from the
list any time it is deactivated, made current, or fails to push.
This works because a task only needs to be attempted to push once.
After an initial failure to push, the other cpus will eventually try to
pull the task when the conditions are proper. This also solves the
problem that we don't completely analyze all tasks due to encountering
an unpushable tasks. Now every task will have a push attempted (when
appropriate).
This reduces latency both by shorting the critical section of the
rq->lock for certain workloads, and by making sure the algorithm
considers all eligible tasks in the system.
[ rostedt: added a couple more BUG_ONs ]
Signed-off-by: Gregory Haskins <ghaskins@novell.com>
Acked-by: Steven Rostedt <srostedt@redhat.com>
2008-12-29 14:39:53 +00:00
|
|
|
BUG_ON(!rt_task(p));
|
|
|
|
|
|
|
|
return p;
|
|
|
|
}
|
|
|
|
|
2008-01-25 20:08:05 +00:00
|
|
|
/*
|
|
|
|
* If the current CPU has more than one RT task, see if the non
|
|
|
|
* running task can migrate over to a CPU that is running a task
|
|
|
|
* of lesser priority.
|
|
|
|
*/
|
2020-09-28 15:06:07 +00:00
|
|
|
static int push_rt_task(struct rq *rq, bool pull)
|
2008-01-25 20:08:05 +00:00
|
|
|
{
|
|
|
|
struct task_struct *next_task;
|
|
|
|
struct rq *lowest_rq;
|
2011-06-17 01:55:20 +00:00
|
|
|
int ret = 0;
|
2008-01-25 20:08:05 +00:00
|
|
|
|
2008-01-25 20:08:12 +00:00
|
|
|
if (!rq->rt.overloaded)
|
|
|
|
return 0;
|
|
|
|
|
sched: create "pushable_tasks" list to limit pushing to one attempt
The RT scheduler employs a "push/pull" design to actively balance tasks
within the system (on a per disjoint cpuset basis). When a task is
awoken, it is immediately determined if there are any lower priority
cpus which should be preempted. This is opposed to the way normal
SCHED_OTHER tasks behave, which will wait for a periodic rebalancing
operation to occur before spreading out load.
When a particular RQ has more than 1 active RT task, it is said to
be in an "overloaded" state. Once this occurs, the system enters
the active balancing mode, where it will try to push the task away,
or persuade a different cpu to pull it over. The system will stay
in this state until the system falls back below the <= 1 queued RT
task per RQ.
However, the current implementation suffers from a limitation in the
push logic. Once overloaded, all tasks (other than current) on the
RQ are analyzed on every push operation, even if it was previously
unpushable (due to affinity, etc). Whats more, the operation stops
at the first task that is unpushable and will not look at items
lower in the queue. This causes two problems:
1) We can have the same tasks analyzed over and over again during each
push, which extends out the fast path in the scheduler for no
gain. Consider a RQ that has dozens of tasks that are bound to a
core. Each one of those tasks will be encountered and skipped
for each push operation while they are queued.
2) There may be lower-priority tasks under the unpushable task that
could have been successfully pushed, but will never be considered
until either the unpushable task is cleared, or a pull operation
succeeds. The net result is a potential latency source for mid
priority tasks.
This patch aims to rectify these two conditions by introducing a new
priority sorted list: "pushable_tasks". A task is added to the list
each time a task is activated or preempted. It is removed from the
list any time it is deactivated, made current, or fails to push.
This works because a task only needs to be attempted to push once.
After an initial failure to push, the other cpus will eventually try to
pull the task when the conditions are proper. This also solves the
problem that we don't completely analyze all tasks due to encountering
an unpushable tasks. Now every task will have a push attempted (when
appropriate).
This reduces latency both by shorting the critical section of the
rq->lock for certain workloads, and by making sure the algorithm
considers all eligible tasks in the system.
[ rostedt: added a couple more BUG_ONs ]
Signed-off-by: Gregory Haskins <ghaskins@novell.com>
Acked-by: Steven Rostedt <srostedt@redhat.com>
2008-12-29 14:39:53 +00:00
|
|
|
next_task = pick_next_pushable_task(rq);
|
2008-01-25 20:08:05 +00:00
|
|
|
if (!next_task)
|
|
|
|
return 0;
|
|
|
|
|
2010-10-17 19:46:10 +00:00
|
|
|
retry:
|
2022-01-27 15:40:59 +00:00
|
|
|
/*
|
|
|
|
* It's possible that the next_task slipped in of
|
|
|
|
* higher priority than current. If that's the case
|
|
|
|
* just reschedule current.
|
|
|
|
*/
|
|
|
|
if (unlikely(next_task->prio < rq->curr->prio)) {
|
|
|
|
resched_curr(rq);
|
|
|
|
return 0;
|
|
|
|
}
|
|
|
|
|
2020-09-28 15:06:07 +00:00
|
|
|
if (is_migration_disabled(next_task)) {
|
|
|
|
struct task_struct *push_task = NULL;
|
|
|
|
int cpu;
|
|
|
|
|
|
|
|
if (!pull || rq->push_busy)
|
|
|
|
return 0;
|
|
|
|
|
2022-01-27 15:40:59 +00:00
|
|
|
/*
|
|
|
|
* Invoking find_lowest_rq() on anything but an RT task doesn't
|
|
|
|
* make sense. Per the above priority check, curr has to
|
|
|
|
* be of higher priority than next_task, so no need to
|
|
|
|
* reschedule when bailing out.
|
|
|
|
*
|
|
|
|
* Note that the stoppers are masqueraded as SCHED_FIFO
|
|
|
|
* (cf. sched_set_stop_task()), so we can't rely on rt_task().
|
|
|
|
*/
|
|
|
|
if (rq->curr->sched_class != &rt_sched_class)
|
|
|
|
return 0;
|
|
|
|
|
2020-09-28 15:06:07 +00:00
|
|
|
cpu = find_lowest_rq(rq->curr);
|
|
|
|
if (cpu == -1 || cpu == rq->cpu)
|
|
|
|
return 0;
|
|
|
|
|
|
|
|
/*
|
|
|
|
* Given we found a CPU with lower priority than @next_task,
|
|
|
|
* therefore it should be running. However we cannot migrate it
|
|
|
|
* to this other CPU, instead attempt to push the current
|
|
|
|
* running task on this CPU away.
|
|
|
|
*/
|
|
|
|
push_task = get_push_task(rq);
|
|
|
|
if (push_task) {
|
2020-11-17 23:19:31 +00:00
|
|
|
raw_spin_rq_unlock(rq);
|
2020-09-28 15:06:07 +00:00
|
|
|
stop_one_cpu_nowait(rq->cpu, push_cpu_stop,
|
|
|
|
push_task, &rq->push_work);
|
2020-11-17 23:19:31 +00:00
|
|
|
raw_spin_rq_lock(rq);
|
2020-09-28 15:06:07 +00:00
|
|
|
}
|
|
|
|
|
|
|
|
return 0;
|
|
|
|
}
|
|
|
|
|
2018-11-03 17:26:02 +00:00
|
|
|
if (WARN_ON(next_task == rq->curr))
|
2008-01-25 20:08:05 +00:00
|
|
|
return 0;
|
|
|
|
|
2008-01-25 20:08:09 +00:00
|
|
|
/* We might release rq lock */
|
2008-01-25 20:08:05 +00:00
|
|
|
get_task_struct(next_task);
|
|
|
|
|
|
|
|
/* find_lock_lowest_rq locks the rq if found */
|
2008-01-25 20:08:09 +00:00
|
|
|
lowest_rq = find_lock_lowest_rq(next_task, rq);
|
2008-01-25 20:08:05 +00:00
|
|
|
if (!lowest_rq) {
|
|
|
|
struct task_struct *task;
|
|
|
|
/*
|
2011-06-17 01:55:20 +00:00
|
|
|
* find_lock_lowest_rq releases rq->lock
|
2008-12-29 14:39:53 +00:00
|
|
|
* so it is possible that next_task has migrated.
|
|
|
|
*
|
|
|
|
* We need to make sure that the task is still on the same
|
|
|
|
* run-queue and is also still the next task eligible for
|
|
|
|
* pushing.
|
2008-01-25 20:08:05 +00:00
|
|
|
*/
|
sched: create "pushable_tasks" list to limit pushing to one attempt
The RT scheduler employs a "push/pull" design to actively balance tasks
within the system (on a per disjoint cpuset basis). When a task is
awoken, it is immediately determined if there are any lower priority
cpus which should be preempted. This is opposed to the way normal
SCHED_OTHER tasks behave, which will wait for a periodic rebalancing
operation to occur before spreading out load.
When a particular RQ has more than 1 active RT task, it is said to
be in an "overloaded" state. Once this occurs, the system enters
the active balancing mode, where it will try to push the task away,
or persuade a different cpu to pull it over. The system will stay
in this state until the system falls back below the <= 1 queued RT
task per RQ.
However, the current implementation suffers from a limitation in the
push logic. Once overloaded, all tasks (other than current) on the
RQ are analyzed on every push operation, even if it was previously
unpushable (due to affinity, etc). Whats more, the operation stops
at the first task that is unpushable and will not look at items
lower in the queue. This causes two problems:
1) We can have the same tasks analyzed over and over again during each
push, which extends out the fast path in the scheduler for no
gain. Consider a RQ that has dozens of tasks that are bound to a
core. Each one of those tasks will be encountered and skipped
for each push operation while they are queued.
2) There may be lower-priority tasks under the unpushable task that
could have been successfully pushed, but will never be considered
until either the unpushable task is cleared, or a pull operation
succeeds. The net result is a potential latency source for mid
priority tasks.
This patch aims to rectify these two conditions by introducing a new
priority sorted list: "pushable_tasks". A task is added to the list
each time a task is activated or preempted. It is removed from the
list any time it is deactivated, made current, or fails to push.
This works because a task only needs to be attempted to push once.
After an initial failure to push, the other cpus will eventually try to
pull the task when the conditions are proper. This also solves the
problem that we don't completely analyze all tasks due to encountering
an unpushable tasks. Now every task will have a push attempted (when
appropriate).
This reduces latency both by shorting the critical section of the
rq->lock for certain workloads, and by making sure the algorithm
considers all eligible tasks in the system.
[ rostedt: added a couple more BUG_ONs ]
Signed-off-by: Gregory Haskins <ghaskins@novell.com>
Acked-by: Steven Rostedt <srostedt@redhat.com>
2008-12-29 14:39:53 +00:00
|
|
|
task = pick_next_pushable_task(rq);
|
2017-05-12 01:05:43 +00:00
|
|
|
if (task == next_task) {
|
2008-12-29 14:39:53 +00:00
|
|
|
/*
|
2011-06-17 01:55:20 +00:00
|
|
|
* The task hasn't migrated, and is still the next
|
|
|
|
* eligible task, but we failed to find a run-queue
|
|
|
|
* to push it to. Do not retry in this case, since
|
sched: Clean up and harmonize the coding style of the scheduler code base
A good number of small style inconsistencies have accumulated
in the scheduler core, so do a pass over them to harmonize
all these details:
- fix speling in comments,
- use curly braces for multi-line statements,
- remove unnecessary parentheses from integer literals,
- capitalize consistently,
- remove stray newlines,
- add comments where necessary,
- remove invalid/unnecessary comments,
- align structure definitions and other data types vertically,
- add missing newlines for increased readability,
- fix vertical tabulation where it's misaligned,
- harmonize preprocessor conditional block labeling
and vertical alignment,
- remove line-breaks where they uglify the code,
- add newline after local variable definitions,
No change in functionality:
md5:
1191fa0a890cfa8132156d2959d7e9e2 built-in.o.before.asm
1191fa0a890cfa8132156d2959d7e9e2 built-in.o.after.asm
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-03-03 13:01:12 +00:00
|
|
|
* other CPUs will pull from us when ready.
|
2008-12-29 14:39:53 +00:00
|
|
|
*/
|
|
|
|
goto out;
|
2008-01-25 20:08:05 +00:00
|
|
|
}
|
sched: create "pushable_tasks" list to limit pushing to one attempt
The RT scheduler employs a "push/pull" design to actively balance tasks
within the system (on a per disjoint cpuset basis). When a task is
awoken, it is immediately determined if there are any lower priority
cpus which should be preempted. This is opposed to the way normal
SCHED_OTHER tasks behave, which will wait for a periodic rebalancing
operation to occur before spreading out load.
When a particular RQ has more than 1 active RT task, it is said to
be in an "overloaded" state. Once this occurs, the system enters
the active balancing mode, where it will try to push the task away,
or persuade a different cpu to pull it over. The system will stay
in this state until the system falls back below the <= 1 queued RT
task per RQ.
However, the current implementation suffers from a limitation in the
push logic. Once overloaded, all tasks (other than current) on the
RQ are analyzed on every push operation, even if it was previously
unpushable (due to affinity, etc). Whats more, the operation stops
at the first task that is unpushable and will not look at items
lower in the queue. This causes two problems:
1) We can have the same tasks analyzed over and over again during each
push, which extends out the fast path in the scheduler for no
gain. Consider a RQ that has dozens of tasks that are bound to a
core. Each one of those tasks will be encountered and skipped
for each push operation while they are queued.
2) There may be lower-priority tasks under the unpushable task that
could have been successfully pushed, but will never be considered
until either the unpushable task is cleared, or a pull operation
succeeds. The net result is a potential latency source for mid
priority tasks.
This patch aims to rectify these two conditions by introducing a new
priority sorted list: "pushable_tasks". A task is added to the list
each time a task is activated or preempted. It is removed from the
list any time it is deactivated, made current, or fails to push.
This works because a task only needs to be attempted to push once.
After an initial failure to push, the other cpus will eventually try to
pull the task when the conditions are proper. This also solves the
problem that we don't completely analyze all tasks due to encountering
an unpushable tasks. Now every task will have a push attempted (when
appropriate).
This reduces latency both by shorting the critical section of the
rq->lock for certain workloads, and by making sure the algorithm
considers all eligible tasks in the system.
[ rostedt: added a couple more BUG_ONs ]
Signed-off-by: Gregory Haskins <ghaskins@novell.com>
Acked-by: Steven Rostedt <srostedt@redhat.com>
2008-12-29 14:39:53 +00:00
|
|
|
|
2008-12-29 14:39:53 +00:00
|
|
|
if (!task)
|
|
|
|
/* No more tasks, just exit */
|
|
|
|
goto out;
|
|
|
|
|
sched: create "pushable_tasks" list to limit pushing to one attempt
The RT scheduler employs a "push/pull" design to actively balance tasks
within the system (on a per disjoint cpuset basis). When a task is
awoken, it is immediately determined if there are any lower priority
cpus which should be preempted. This is opposed to the way normal
SCHED_OTHER tasks behave, which will wait for a periodic rebalancing
operation to occur before spreading out load.
When a particular RQ has more than 1 active RT task, it is said to
be in an "overloaded" state. Once this occurs, the system enters
the active balancing mode, where it will try to push the task away,
or persuade a different cpu to pull it over. The system will stay
in this state until the system falls back below the <= 1 queued RT
task per RQ.
However, the current implementation suffers from a limitation in the
push logic. Once overloaded, all tasks (other than current) on the
RQ are analyzed on every push operation, even if it was previously
unpushable (due to affinity, etc). Whats more, the operation stops
at the first task that is unpushable and will not look at items
lower in the queue. This causes two problems:
1) We can have the same tasks analyzed over and over again during each
push, which extends out the fast path in the scheduler for no
gain. Consider a RQ that has dozens of tasks that are bound to a
core. Each one of those tasks will be encountered and skipped
for each push operation while they are queued.
2) There may be lower-priority tasks under the unpushable task that
could have been successfully pushed, but will never be considered
until either the unpushable task is cleared, or a pull operation
succeeds. The net result is a potential latency source for mid
priority tasks.
This patch aims to rectify these two conditions by introducing a new
priority sorted list: "pushable_tasks". A task is added to the list
each time a task is activated or preempted. It is removed from the
list any time it is deactivated, made current, or fails to push.
This works because a task only needs to be attempted to push once.
After an initial failure to push, the other cpus will eventually try to
pull the task when the conditions are proper. This also solves the
problem that we don't completely analyze all tasks due to encountering
an unpushable tasks. Now every task will have a push attempted (when
appropriate).
This reduces latency both by shorting the critical section of the
rq->lock for certain workloads, and by making sure the algorithm
considers all eligible tasks in the system.
[ rostedt: added a couple more BUG_ONs ]
Signed-off-by: Gregory Haskins <ghaskins@novell.com>
Acked-by: Steven Rostedt <srostedt@redhat.com>
2008-12-29 14:39:53 +00:00
|
|
|
/*
|
2008-12-29 14:39:53 +00:00
|
|
|
* Something has shifted, try again.
|
sched: create "pushable_tasks" list to limit pushing to one attempt
The RT scheduler employs a "push/pull" design to actively balance tasks
within the system (on a per disjoint cpuset basis). When a task is
awoken, it is immediately determined if there are any lower priority
cpus which should be preempted. This is opposed to the way normal
SCHED_OTHER tasks behave, which will wait for a periodic rebalancing
operation to occur before spreading out load.
When a particular RQ has more than 1 active RT task, it is said to
be in an "overloaded" state. Once this occurs, the system enters
the active balancing mode, where it will try to push the task away,
or persuade a different cpu to pull it over. The system will stay
in this state until the system falls back below the <= 1 queued RT
task per RQ.
However, the current implementation suffers from a limitation in the
push logic. Once overloaded, all tasks (other than current) on the
RQ are analyzed on every push operation, even if it was previously
unpushable (due to affinity, etc). Whats more, the operation stops
at the first task that is unpushable and will not look at items
lower in the queue. This causes two problems:
1) We can have the same tasks analyzed over and over again during each
push, which extends out the fast path in the scheduler for no
gain. Consider a RQ that has dozens of tasks that are bound to a
core. Each one of those tasks will be encountered and skipped
for each push operation while they are queued.
2) There may be lower-priority tasks under the unpushable task that
could have been successfully pushed, but will never be considered
until either the unpushable task is cleared, or a pull operation
succeeds. The net result is a potential latency source for mid
priority tasks.
This patch aims to rectify these two conditions by introducing a new
priority sorted list: "pushable_tasks". A task is added to the list
each time a task is activated or preempted. It is removed from the
list any time it is deactivated, made current, or fails to push.
This works because a task only needs to be attempted to push once.
After an initial failure to push, the other cpus will eventually try to
pull the task when the conditions are proper. This also solves the
problem that we don't completely analyze all tasks due to encountering
an unpushable tasks. Now every task will have a push attempted (when
appropriate).
This reduces latency both by shorting the critical section of the
rq->lock for certain workloads, and by making sure the algorithm
considers all eligible tasks in the system.
[ rostedt: added a couple more BUG_ONs ]
Signed-off-by: Gregory Haskins <ghaskins@novell.com>
Acked-by: Steven Rostedt <srostedt@redhat.com>
2008-12-29 14:39:53 +00:00
|
|
|
*/
|
2008-12-29 14:39:53 +00:00
|
|
|
put_task_struct(next_task);
|
|
|
|
next_task = task;
|
|
|
|
goto retry;
|
2008-01-25 20:08:05 +00:00
|
|
|
}
|
|
|
|
|
2008-01-25 20:08:09 +00:00
|
|
|
deactivate_task(rq, next_task, 0);
|
2008-01-25 20:08:05 +00:00
|
|
|
set_task_cpu(next_task, lowest_rq->cpu);
|
|
|
|
activate_task(lowest_rq, next_task, 0);
|
2014-06-28 20:03:57 +00:00
|
|
|
resched_curr(lowest_rq);
|
2020-09-28 15:06:07 +00:00
|
|
|
ret = 1;
|
2008-01-25 20:08:05 +00:00
|
|
|
|
2008-08-11 07:30:22 +00:00
|
|
|
double_unlock_balance(rq, lowest_rq);
|
2008-01-25 20:08:05 +00:00
|
|
|
out:
|
|
|
|
put_task_struct(next_task);
|
|
|
|
|
2011-06-17 01:55:20 +00:00
|
|
|
return ret;
|
2008-01-25 20:08:05 +00:00
|
|
|
}
|
|
|
|
|
|
|
|
static void push_rt_tasks(struct rq *rq)
|
|
|
|
{
|
|
|
|
/* push_rt_task will return true if it moved an RT */
|
2020-09-28 15:06:07 +00:00
|
|
|
while (push_rt_task(rq, false))
|
2008-01-25 20:08:05 +00:00
|
|
|
;
|
|
|
|
}
|
|
|
|
|
sched/rt: Use IPI to trigger RT task push migration instead of pulling
When debugging the latencies on a 40 core box, where we hit 300 to
500 microsecond latencies, I found there was a huge contention on the
runqueue locks.
Investigating it further, running ftrace, I found that it was due to
the pulling of RT tasks.
The test that was run was the following:
cyclictest --numa -p95 -m -d0 -i100
This created a thread on each CPU, that would set its wakeup in iterations
of 100 microseconds. The -d0 means that all the threads had the same
interval (100us). Each thread sleeps for 100us and wakes up and measures
its latencies.
cyclictest is maintained at:
git://git.kernel.org/pub/scm/linux/kernel/git/clrkwllms/rt-tests.git
What happened was another RT task would be scheduled on one of the CPUs
that was running our test, when the other CPU tests went to sleep and
scheduled idle. This caused the "pull" operation to execute on all
these CPUs. Each one of these saw the RT task that was overloaded on
the CPU of the test that was still running, and each one tried
to grab that task in a thundering herd way.
To grab the task, each thread would do a double rq lock grab, grabbing
its own lock as well as the rq of the overloaded CPU. As the sched
domains on this box was rather flat for its size, I saw up to 12 CPUs
block on this lock at once. This caused a ripple affect with the
rq locks especially since the taking was done via a double rq lock, which
means that several of the CPUs had their own rq locks held while trying
to take this rq lock. As these locks were blocked, any wakeups or load
balanceing on these CPUs would also block on these locks, and the wait
time escalated.
I've tried various methods to lessen the load, but things like an
atomic counter to only let one CPU grab the task wont work, because
the task may have a limited affinity, and we may pick the wrong
CPU to take that lock and do the pull, to only find out that the
CPU we picked isn't in the task's affinity.
Instead of doing the PULL, I now have the CPUs that want the pull to
send over an IPI to the overloaded CPU, and let that CPU pick what
CPU to push the task to. No more need to grab the rq lock, and the
push/pull algorithm still works fine.
With this patch, the latency dropped to just 150us over a 20 hour run.
Without the patch, the huge latencies would trigger in seconds.
I've created a new sched feature called RT_PUSH_IPI, which is enabled
by default.
When RT_PUSH_IPI is not enabled, the old method of grabbing the rq locks
and having the pulling CPU do the work is implemented. When RT_PUSH_IPI
is enabled, the IPI is sent to the overloaded CPU to do a push.
To enabled or disable this at run time:
# mount -t debugfs nodev /sys/kernel/debug
# echo RT_PUSH_IPI > /sys/kernel/debug/sched_features
or
# echo NO_RT_PUSH_IPI > /sys/kernel/debug/sched_features
Update: This original patch would send an IPI to all CPUs in the RT overload
list. But that could theoretically cause the reverse issue. That is, there
could be lots of overloaded RT queues and one CPU lowers its priority. It would
then send an IPI to all the overloaded RT queues and they could then all try
to grab the rq lock of the CPU lowering its priority, and then we have the
same problem.
The latest design sends out only one IPI to the first overloaded CPU. It tries to
push any tasks that it can, and then looks for the next overloaded CPU that can
push to the source CPU. The IPIs stop when all overloaded CPUs that have pushable
tasks that have priorities greater than the source CPU are covered. In case the
source CPU lowers its priority again, a flag is set to tell the IPI traversal to
restart with the first RT overloaded CPU after the source CPU.
Parts-suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Joern Engel <joern@purestorage.com>
Cc: Clark Williams <williams@redhat.com>
Cc: Mike Galbraith <umgwanakikbuti@gmail.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20150318144946.2f3cc982@gandalf.local.home
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2015-03-18 18:49:46 +00:00
|
|
|
#ifdef HAVE_RT_PUSH_IPI
|
sched/rt: Simplify the IPI based RT balancing logic
When a CPU lowers its priority (schedules out a high priority task for a
lower priority one), a check is made to see if any other CPU has overloaded
RT tasks (more than one). It checks the rto_mask to determine this and if so
it will request to pull one of those tasks to itself if the non running RT
task is of higher priority than the new priority of the next task to run on
the current CPU.
When we deal with large number of CPUs, the original pull logic suffered
from large lock contention on a single CPU run queue, which caused a huge
latency across all CPUs. This was caused by only having one CPU having
overloaded RT tasks and a bunch of other CPUs lowering their priority. To
solve this issue, commit:
b6366f048e0c ("sched/rt: Use IPI to trigger RT task push migration instead of pulling")
changed the way to request a pull. Instead of grabbing the lock of the
overloaded CPU's runqueue, it simply sent an IPI to that CPU to do the work.
Although the IPI logic worked very well in removing the large latency build
up, it still could suffer from a large number of IPIs being sent to a single
CPU. On a 80 CPU box, I measured over 200us of processing IPIs. Worse yet,
when I tested this on a 120 CPU box, with a stress test that had lots of
RT tasks scheduling on all CPUs, it actually triggered the hard lockup
detector! One CPU had so many IPIs sent to it, and due to the restart
mechanism that is triggered when the source run queue has a priority status
change, the CPU spent minutes! processing the IPIs.
Thinking about this further, I realized there's no reason for each run queue
to send its own IPI. As all CPUs with overloaded tasks must be scanned
regardless if there's one or many CPUs lowering their priority, because
there's no current way to find the CPU with the highest priority task that
can schedule to one of these CPUs, there really only needs to be one IPI
being sent around at a time.
This greatly simplifies the code!
The new approach is to have each root domain have its own irq work, as the
rto_mask is per root domain. The root domain has the following fields
attached to it:
rto_push_work - the irq work to process each CPU set in rto_mask
rto_lock - the lock to protect some of the other rto fields
rto_loop_start - an atomic that keeps contention down on rto_lock
the first CPU scheduling in a lower priority task
is the one to kick off the process.
rto_loop_next - an atomic that gets incremented for each CPU that
schedules in a lower priority task.
rto_loop - a variable protected by rto_lock that is used to
compare against rto_loop_next
rto_cpu - The cpu to send the next IPI to, also protected by
the rto_lock.
When a CPU schedules in a lower priority task and wants to make sure
overloaded CPUs know about it. It increments the rto_loop_next. Then it
atomically sets rto_loop_start with a cmpxchg. If the old value is not "0",
then it is done, as another CPU is kicking off the IPI loop. If the old
value is "0", then it will take the rto_lock to synchronize with a possible
IPI being sent around to the overloaded CPUs.
If rto_cpu is greater than or equal to nr_cpu_ids, then there's either no
IPI being sent around, or one is about to finish. Then rto_cpu is set to the
first CPU in rto_mask and an IPI is sent to that CPU. If there's no CPUs set
in rto_mask, then there's nothing to be done.
When the CPU receives the IPI, it will first try to push any RT tasks that is
queued on the CPU but can't run because a higher priority RT task is
currently running on that CPU.
Then it takes the rto_lock and looks for the next CPU in the rto_mask. If it
finds one, it simply sends an IPI to that CPU and the process continues.
If there's no more CPUs in the rto_mask, then rto_loop is compared with
rto_loop_next. If they match, everything is done and the process is over. If
they do not match, then a CPU scheduled in a lower priority task as the IPI
was being passed around, and the process needs to start again. The first CPU
in rto_mask is sent the IPI.
This change removes this duplication of work in the IPI logic, and greatly
lowers the latency caused by the IPIs. This removed the lockup happening on
the 120 CPU machine. It also simplifies the code tremendously. What else
could anyone ask for?
Thanks to Peter Zijlstra for simplifying the rto_loop_start atomic logic and
supplying me with the rto_start_trylock() and rto_start_unlock() helper
functions.
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Clark Williams <williams@redhat.com>
Cc: Daniel Bristot de Oliveira <bristot@redhat.com>
Cc: John Kacur <jkacur@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Scott Wood <swood@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20170424114732.1aac6dc4@gandalf.local.home
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-10-06 18:05:04 +00:00
|
|
|
|
sched/rt: Use IPI to trigger RT task push migration instead of pulling
When debugging the latencies on a 40 core box, where we hit 300 to
500 microsecond latencies, I found there was a huge contention on the
runqueue locks.
Investigating it further, running ftrace, I found that it was due to
the pulling of RT tasks.
The test that was run was the following:
cyclictest --numa -p95 -m -d0 -i100
This created a thread on each CPU, that would set its wakeup in iterations
of 100 microseconds. The -d0 means that all the threads had the same
interval (100us). Each thread sleeps for 100us and wakes up and measures
its latencies.
cyclictest is maintained at:
git://git.kernel.org/pub/scm/linux/kernel/git/clrkwllms/rt-tests.git
What happened was another RT task would be scheduled on one of the CPUs
that was running our test, when the other CPU tests went to sleep and
scheduled idle. This caused the "pull" operation to execute on all
these CPUs. Each one of these saw the RT task that was overloaded on
the CPU of the test that was still running, and each one tried
to grab that task in a thundering herd way.
To grab the task, each thread would do a double rq lock grab, grabbing
its own lock as well as the rq of the overloaded CPU. As the sched
domains on this box was rather flat for its size, I saw up to 12 CPUs
block on this lock at once. This caused a ripple affect with the
rq locks especially since the taking was done via a double rq lock, which
means that several of the CPUs had their own rq locks held while trying
to take this rq lock. As these locks were blocked, any wakeups or load
balanceing on these CPUs would also block on these locks, and the wait
time escalated.
I've tried various methods to lessen the load, but things like an
atomic counter to only let one CPU grab the task wont work, because
the task may have a limited affinity, and we may pick the wrong
CPU to take that lock and do the pull, to only find out that the
CPU we picked isn't in the task's affinity.
Instead of doing the PULL, I now have the CPUs that want the pull to
send over an IPI to the overloaded CPU, and let that CPU pick what
CPU to push the task to. No more need to grab the rq lock, and the
push/pull algorithm still works fine.
With this patch, the latency dropped to just 150us over a 20 hour run.
Without the patch, the huge latencies would trigger in seconds.
I've created a new sched feature called RT_PUSH_IPI, which is enabled
by default.
When RT_PUSH_IPI is not enabled, the old method of grabbing the rq locks
and having the pulling CPU do the work is implemented. When RT_PUSH_IPI
is enabled, the IPI is sent to the overloaded CPU to do a push.
To enabled or disable this at run time:
# mount -t debugfs nodev /sys/kernel/debug
# echo RT_PUSH_IPI > /sys/kernel/debug/sched_features
or
# echo NO_RT_PUSH_IPI > /sys/kernel/debug/sched_features
Update: This original patch would send an IPI to all CPUs in the RT overload
list. But that could theoretically cause the reverse issue. That is, there
could be lots of overloaded RT queues and one CPU lowers its priority. It would
then send an IPI to all the overloaded RT queues and they could then all try
to grab the rq lock of the CPU lowering its priority, and then we have the
same problem.
The latest design sends out only one IPI to the first overloaded CPU. It tries to
push any tasks that it can, and then looks for the next overloaded CPU that can
push to the source CPU. The IPIs stop when all overloaded CPUs that have pushable
tasks that have priorities greater than the source CPU are covered. In case the
source CPU lowers its priority again, a flag is set to tell the IPI traversal to
restart with the first RT overloaded CPU after the source CPU.
Parts-suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Joern Engel <joern@purestorage.com>
Cc: Clark Williams <williams@redhat.com>
Cc: Mike Galbraith <umgwanakikbuti@gmail.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20150318144946.2f3cc982@gandalf.local.home
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2015-03-18 18:49:46 +00:00
|
|
|
/*
|
sched/rt: Simplify the IPI based RT balancing logic
When a CPU lowers its priority (schedules out a high priority task for a
lower priority one), a check is made to see if any other CPU has overloaded
RT tasks (more than one). It checks the rto_mask to determine this and if so
it will request to pull one of those tasks to itself if the non running RT
task is of higher priority than the new priority of the next task to run on
the current CPU.
When we deal with large number of CPUs, the original pull logic suffered
from large lock contention on a single CPU run queue, which caused a huge
latency across all CPUs. This was caused by only having one CPU having
overloaded RT tasks and a bunch of other CPUs lowering their priority. To
solve this issue, commit:
b6366f048e0c ("sched/rt: Use IPI to trigger RT task push migration instead of pulling")
changed the way to request a pull. Instead of grabbing the lock of the
overloaded CPU's runqueue, it simply sent an IPI to that CPU to do the work.
Although the IPI logic worked very well in removing the large latency build
up, it still could suffer from a large number of IPIs being sent to a single
CPU. On a 80 CPU box, I measured over 200us of processing IPIs. Worse yet,
when I tested this on a 120 CPU box, with a stress test that had lots of
RT tasks scheduling on all CPUs, it actually triggered the hard lockup
detector! One CPU had so many IPIs sent to it, and due to the restart
mechanism that is triggered when the source run queue has a priority status
change, the CPU spent minutes! processing the IPIs.
Thinking about this further, I realized there's no reason for each run queue
to send its own IPI. As all CPUs with overloaded tasks must be scanned
regardless if there's one or many CPUs lowering their priority, because
there's no current way to find the CPU with the highest priority task that
can schedule to one of these CPUs, there really only needs to be one IPI
being sent around at a time.
This greatly simplifies the code!
The new approach is to have each root domain have its own irq work, as the
rto_mask is per root domain. The root domain has the following fields
attached to it:
rto_push_work - the irq work to process each CPU set in rto_mask
rto_lock - the lock to protect some of the other rto fields
rto_loop_start - an atomic that keeps contention down on rto_lock
the first CPU scheduling in a lower priority task
is the one to kick off the process.
rto_loop_next - an atomic that gets incremented for each CPU that
schedules in a lower priority task.
rto_loop - a variable protected by rto_lock that is used to
compare against rto_loop_next
rto_cpu - The cpu to send the next IPI to, also protected by
the rto_lock.
When a CPU schedules in a lower priority task and wants to make sure
overloaded CPUs know about it. It increments the rto_loop_next. Then it
atomically sets rto_loop_start with a cmpxchg. If the old value is not "0",
then it is done, as another CPU is kicking off the IPI loop. If the old
value is "0", then it will take the rto_lock to synchronize with a possible
IPI being sent around to the overloaded CPUs.
If rto_cpu is greater than or equal to nr_cpu_ids, then there's either no
IPI being sent around, or one is about to finish. Then rto_cpu is set to the
first CPU in rto_mask and an IPI is sent to that CPU. If there's no CPUs set
in rto_mask, then there's nothing to be done.
When the CPU receives the IPI, it will first try to push any RT tasks that is
queued on the CPU but can't run because a higher priority RT task is
currently running on that CPU.
Then it takes the rto_lock and looks for the next CPU in the rto_mask. If it
finds one, it simply sends an IPI to that CPU and the process continues.
If there's no more CPUs in the rto_mask, then rto_loop is compared with
rto_loop_next. If they match, everything is done and the process is over. If
they do not match, then a CPU scheduled in a lower priority task as the IPI
was being passed around, and the process needs to start again. The first CPU
in rto_mask is sent the IPI.
This change removes this duplication of work in the IPI logic, and greatly
lowers the latency caused by the IPIs. This removed the lockup happening on
the 120 CPU machine. It also simplifies the code tremendously. What else
could anyone ask for?
Thanks to Peter Zijlstra for simplifying the rto_loop_start atomic logic and
supplying me with the rto_start_trylock() and rto_start_unlock() helper
functions.
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Clark Williams <williams@redhat.com>
Cc: Daniel Bristot de Oliveira <bristot@redhat.com>
Cc: John Kacur <jkacur@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Scott Wood <swood@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20170424114732.1aac6dc4@gandalf.local.home
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-10-06 18:05:04 +00:00
|
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* When a high priority task schedules out from a CPU and a lower priority
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* task is scheduled in, a check is made to see if there's any RT tasks
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* on other CPUs that are waiting to run because a higher priority RT task
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* is currently running on its CPU. In this case, the CPU with multiple RT
|
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* tasks queued on it (overloaded) needs to be notified that a CPU has opened
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* up that may be able to run one of its non-running queued RT tasks.
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*
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* All CPUs with overloaded RT tasks need to be notified as there is currently
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* no way to know which of these CPUs have the highest priority task waiting
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* to run. Instead of trying to take a spinlock on each of these CPUs,
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* which has shown to cause large latency when done on machines with many
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* CPUs, sending an IPI to the CPUs to have them push off the overloaded
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* RT tasks waiting to run.
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*
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* Just sending an IPI to each of the CPUs is also an issue, as on large
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* count CPU machines, this can cause an IPI storm on a CPU, especially
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* if its the only CPU with multiple RT tasks queued, and a large number
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* of CPUs scheduling a lower priority task at the same time.
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*
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* Each root domain has its own irq work function that can iterate over
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* all CPUs with RT overloaded tasks. Since all CPUs with overloaded RT
|
2021-03-18 12:38:50 +00:00
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* task must be checked if there's one or many CPUs that are lowering
|
sched/rt: Simplify the IPI based RT balancing logic
When a CPU lowers its priority (schedules out a high priority task for a
lower priority one), a check is made to see if any other CPU has overloaded
RT tasks (more than one). It checks the rto_mask to determine this and if so
it will request to pull one of those tasks to itself if the non running RT
task is of higher priority than the new priority of the next task to run on
the current CPU.
When we deal with large number of CPUs, the original pull logic suffered
from large lock contention on a single CPU run queue, which caused a huge
latency across all CPUs. This was caused by only having one CPU having
overloaded RT tasks and a bunch of other CPUs lowering their priority. To
solve this issue, commit:
b6366f048e0c ("sched/rt: Use IPI to trigger RT task push migration instead of pulling")
changed the way to request a pull. Instead of grabbing the lock of the
overloaded CPU's runqueue, it simply sent an IPI to that CPU to do the work.
Although the IPI logic worked very well in removing the large latency build
up, it still could suffer from a large number of IPIs being sent to a single
CPU. On a 80 CPU box, I measured over 200us of processing IPIs. Worse yet,
when I tested this on a 120 CPU box, with a stress test that had lots of
RT tasks scheduling on all CPUs, it actually triggered the hard lockup
detector! One CPU had so many IPIs sent to it, and due to the restart
mechanism that is triggered when the source run queue has a priority status
change, the CPU spent minutes! processing the IPIs.
Thinking about this further, I realized there's no reason for each run queue
to send its own IPI. As all CPUs with overloaded tasks must be scanned
regardless if there's one or many CPUs lowering their priority, because
there's no current way to find the CPU with the highest priority task that
can schedule to one of these CPUs, there really only needs to be one IPI
being sent around at a time.
This greatly simplifies the code!
The new approach is to have each root domain have its own irq work, as the
rto_mask is per root domain. The root domain has the following fields
attached to it:
rto_push_work - the irq work to process each CPU set in rto_mask
rto_lock - the lock to protect some of the other rto fields
rto_loop_start - an atomic that keeps contention down on rto_lock
the first CPU scheduling in a lower priority task
is the one to kick off the process.
rto_loop_next - an atomic that gets incremented for each CPU that
schedules in a lower priority task.
rto_loop - a variable protected by rto_lock that is used to
compare against rto_loop_next
rto_cpu - The cpu to send the next IPI to, also protected by
the rto_lock.
When a CPU schedules in a lower priority task and wants to make sure
overloaded CPUs know about it. It increments the rto_loop_next. Then it
atomically sets rto_loop_start with a cmpxchg. If the old value is not "0",
then it is done, as another CPU is kicking off the IPI loop. If the old
value is "0", then it will take the rto_lock to synchronize with a possible
IPI being sent around to the overloaded CPUs.
If rto_cpu is greater than or equal to nr_cpu_ids, then there's either no
IPI being sent around, or one is about to finish. Then rto_cpu is set to the
first CPU in rto_mask and an IPI is sent to that CPU. If there's no CPUs set
in rto_mask, then there's nothing to be done.
When the CPU receives the IPI, it will first try to push any RT tasks that is
queued on the CPU but can't run because a higher priority RT task is
currently running on that CPU.
Then it takes the rto_lock and looks for the next CPU in the rto_mask. If it
finds one, it simply sends an IPI to that CPU and the process continues.
If there's no more CPUs in the rto_mask, then rto_loop is compared with
rto_loop_next. If they match, everything is done and the process is over. If
they do not match, then a CPU scheduled in a lower priority task as the IPI
was being passed around, and the process needs to start again. The first CPU
in rto_mask is sent the IPI.
This change removes this duplication of work in the IPI logic, and greatly
lowers the latency caused by the IPIs. This removed the lockup happening on
the 120 CPU machine. It also simplifies the code tremendously. What else
could anyone ask for?
Thanks to Peter Zijlstra for simplifying the rto_loop_start atomic logic and
supplying me with the rto_start_trylock() and rto_start_unlock() helper
functions.
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Clark Williams <williams@redhat.com>
Cc: Daniel Bristot de Oliveira <bristot@redhat.com>
Cc: John Kacur <jkacur@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Scott Wood <swood@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20170424114732.1aac6dc4@gandalf.local.home
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-10-06 18:05:04 +00:00
|
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* their priority, there's a single irq work iterator that will try to
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* push off RT tasks that are waiting to run.
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*
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* When a CPU schedules a lower priority task, it will kick off the
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* irq work iterator that will jump to each CPU with overloaded RT tasks.
|
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* As it only takes the first CPU that schedules a lower priority task
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* to start the process, the rto_start variable is incremented and if
|
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* the atomic result is one, then that CPU will try to take the rto_lock.
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* This prevents high contention on the lock as the process handles all
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* CPUs scheduling lower priority tasks.
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*
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* All CPUs that are scheduling a lower priority task will increment the
|
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* rt_loop_next variable. This will make sure that the irq work iterator
|
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* checks all RT overloaded CPUs whenever a CPU schedules a new lower
|
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* priority task, even if the iterator is in the middle of a scan. Incrementing
|
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* the rt_loop_next will cause the iterator to perform another scan.
|
sched/rt: Use IPI to trigger RT task push migration instead of pulling
When debugging the latencies on a 40 core box, where we hit 300 to
500 microsecond latencies, I found there was a huge contention on the
runqueue locks.
Investigating it further, running ftrace, I found that it was due to
the pulling of RT tasks.
The test that was run was the following:
cyclictest --numa -p95 -m -d0 -i100
This created a thread on each CPU, that would set its wakeup in iterations
of 100 microseconds. The -d0 means that all the threads had the same
interval (100us). Each thread sleeps for 100us and wakes up and measures
its latencies.
cyclictest is maintained at:
git://git.kernel.org/pub/scm/linux/kernel/git/clrkwllms/rt-tests.git
What happened was another RT task would be scheduled on one of the CPUs
that was running our test, when the other CPU tests went to sleep and
scheduled idle. This caused the "pull" operation to execute on all
these CPUs. Each one of these saw the RT task that was overloaded on
the CPU of the test that was still running, and each one tried
to grab that task in a thundering herd way.
To grab the task, each thread would do a double rq lock grab, grabbing
its own lock as well as the rq of the overloaded CPU. As the sched
domains on this box was rather flat for its size, I saw up to 12 CPUs
block on this lock at once. This caused a ripple affect with the
rq locks especially since the taking was done via a double rq lock, which
means that several of the CPUs had their own rq locks held while trying
to take this rq lock. As these locks were blocked, any wakeups or load
balanceing on these CPUs would also block on these locks, and the wait
time escalated.
I've tried various methods to lessen the load, but things like an
atomic counter to only let one CPU grab the task wont work, because
the task may have a limited affinity, and we may pick the wrong
CPU to take that lock and do the pull, to only find out that the
CPU we picked isn't in the task's affinity.
Instead of doing the PULL, I now have the CPUs that want the pull to
send over an IPI to the overloaded CPU, and let that CPU pick what
CPU to push the task to. No more need to grab the rq lock, and the
push/pull algorithm still works fine.
With this patch, the latency dropped to just 150us over a 20 hour run.
Without the patch, the huge latencies would trigger in seconds.
I've created a new sched feature called RT_PUSH_IPI, which is enabled
by default.
When RT_PUSH_IPI is not enabled, the old method of grabbing the rq locks
and having the pulling CPU do the work is implemented. When RT_PUSH_IPI
is enabled, the IPI is sent to the overloaded CPU to do a push.
To enabled or disable this at run time:
# mount -t debugfs nodev /sys/kernel/debug
# echo RT_PUSH_IPI > /sys/kernel/debug/sched_features
or
# echo NO_RT_PUSH_IPI > /sys/kernel/debug/sched_features
Update: This original patch would send an IPI to all CPUs in the RT overload
list. But that could theoretically cause the reverse issue. That is, there
could be lots of overloaded RT queues and one CPU lowers its priority. It would
then send an IPI to all the overloaded RT queues and they could then all try
to grab the rq lock of the CPU lowering its priority, and then we have the
same problem.
The latest design sends out only one IPI to the first overloaded CPU. It tries to
push any tasks that it can, and then looks for the next overloaded CPU that can
push to the source CPU. The IPIs stop when all overloaded CPUs that have pushable
tasks that have priorities greater than the source CPU are covered. In case the
source CPU lowers its priority again, a flag is set to tell the IPI traversal to
restart with the first RT overloaded CPU after the source CPU.
Parts-suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Joern Engel <joern@purestorage.com>
Cc: Clark Williams <williams@redhat.com>
Cc: Mike Galbraith <umgwanakikbuti@gmail.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20150318144946.2f3cc982@gandalf.local.home
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2015-03-18 18:49:46 +00:00
|
|
|
*
|
|
|
|
*/
|
2018-01-24 01:45:37 +00:00
|
|
|
static int rto_next_cpu(struct root_domain *rd)
|
sched/rt: Use IPI to trigger RT task push migration instead of pulling
When debugging the latencies on a 40 core box, where we hit 300 to
500 microsecond latencies, I found there was a huge contention on the
runqueue locks.
Investigating it further, running ftrace, I found that it was due to
the pulling of RT tasks.
The test that was run was the following:
cyclictest --numa -p95 -m -d0 -i100
This created a thread on each CPU, that would set its wakeup in iterations
of 100 microseconds. The -d0 means that all the threads had the same
interval (100us). Each thread sleeps for 100us and wakes up and measures
its latencies.
cyclictest is maintained at:
git://git.kernel.org/pub/scm/linux/kernel/git/clrkwllms/rt-tests.git
What happened was another RT task would be scheduled on one of the CPUs
that was running our test, when the other CPU tests went to sleep and
scheduled idle. This caused the "pull" operation to execute on all
these CPUs. Each one of these saw the RT task that was overloaded on
the CPU of the test that was still running, and each one tried
to grab that task in a thundering herd way.
To grab the task, each thread would do a double rq lock grab, grabbing
its own lock as well as the rq of the overloaded CPU. As the sched
domains on this box was rather flat for its size, I saw up to 12 CPUs
block on this lock at once. This caused a ripple affect with the
rq locks especially since the taking was done via a double rq lock, which
means that several of the CPUs had their own rq locks held while trying
to take this rq lock. As these locks were blocked, any wakeups or load
balanceing on these CPUs would also block on these locks, and the wait
time escalated.
I've tried various methods to lessen the load, but things like an
atomic counter to only let one CPU grab the task wont work, because
the task may have a limited affinity, and we may pick the wrong
CPU to take that lock and do the pull, to only find out that the
CPU we picked isn't in the task's affinity.
Instead of doing the PULL, I now have the CPUs that want the pull to
send over an IPI to the overloaded CPU, and let that CPU pick what
CPU to push the task to. No more need to grab the rq lock, and the
push/pull algorithm still works fine.
With this patch, the latency dropped to just 150us over a 20 hour run.
Without the patch, the huge latencies would trigger in seconds.
I've created a new sched feature called RT_PUSH_IPI, which is enabled
by default.
When RT_PUSH_IPI is not enabled, the old method of grabbing the rq locks
and having the pulling CPU do the work is implemented. When RT_PUSH_IPI
is enabled, the IPI is sent to the overloaded CPU to do a push.
To enabled or disable this at run time:
# mount -t debugfs nodev /sys/kernel/debug
# echo RT_PUSH_IPI > /sys/kernel/debug/sched_features
or
# echo NO_RT_PUSH_IPI > /sys/kernel/debug/sched_features
Update: This original patch would send an IPI to all CPUs in the RT overload
list. But that could theoretically cause the reverse issue. That is, there
could be lots of overloaded RT queues and one CPU lowers its priority. It would
then send an IPI to all the overloaded RT queues and they could then all try
to grab the rq lock of the CPU lowering its priority, and then we have the
same problem.
The latest design sends out only one IPI to the first overloaded CPU. It tries to
push any tasks that it can, and then looks for the next overloaded CPU that can
push to the source CPU. The IPIs stop when all overloaded CPUs that have pushable
tasks that have priorities greater than the source CPU are covered. In case the
source CPU lowers its priority again, a flag is set to tell the IPI traversal to
restart with the first RT overloaded CPU after the source CPU.
Parts-suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Joern Engel <joern@purestorage.com>
Cc: Clark Williams <williams@redhat.com>
Cc: Mike Galbraith <umgwanakikbuti@gmail.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20150318144946.2f3cc982@gandalf.local.home
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2015-03-18 18:49:46 +00:00
|
|
|
{
|
sched/rt: Simplify the IPI based RT balancing logic
When a CPU lowers its priority (schedules out a high priority task for a
lower priority one), a check is made to see if any other CPU has overloaded
RT tasks (more than one). It checks the rto_mask to determine this and if so
it will request to pull one of those tasks to itself if the non running RT
task is of higher priority than the new priority of the next task to run on
the current CPU.
When we deal with large number of CPUs, the original pull logic suffered
from large lock contention on a single CPU run queue, which caused a huge
latency across all CPUs. This was caused by only having one CPU having
overloaded RT tasks and a bunch of other CPUs lowering their priority. To
solve this issue, commit:
b6366f048e0c ("sched/rt: Use IPI to trigger RT task push migration instead of pulling")
changed the way to request a pull. Instead of grabbing the lock of the
overloaded CPU's runqueue, it simply sent an IPI to that CPU to do the work.
Although the IPI logic worked very well in removing the large latency build
up, it still could suffer from a large number of IPIs being sent to a single
CPU. On a 80 CPU box, I measured over 200us of processing IPIs. Worse yet,
when I tested this on a 120 CPU box, with a stress test that had lots of
RT tasks scheduling on all CPUs, it actually triggered the hard lockup
detector! One CPU had so many IPIs sent to it, and due to the restart
mechanism that is triggered when the source run queue has a priority status
change, the CPU spent minutes! processing the IPIs.
Thinking about this further, I realized there's no reason for each run queue
to send its own IPI. As all CPUs with overloaded tasks must be scanned
regardless if there's one or many CPUs lowering their priority, because
there's no current way to find the CPU with the highest priority task that
can schedule to one of these CPUs, there really only needs to be one IPI
being sent around at a time.
This greatly simplifies the code!
The new approach is to have each root domain have its own irq work, as the
rto_mask is per root domain. The root domain has the following fields
attached to it:
rto_push_work - the irq work to process each CPU set in rto_mask
rto_lock - the lock to protect some of the other rto fields
rto_loop_start - an atomic that keeps contention down on rto_lock
the first CPU scheduling in a lower priority task
is the one to kick off the process.
rto_loop_next - an atomic that gets incremented for each CPU that
schedules in a lower priority task.
rto_loop - a variable protected by rto_lock that is used to
compare against rto_loop_next
rto_cpu - The cpu to send the next IPI to, also protected by
the rto_lock.
When a CPU schedules in a lower priority task and wants to make sure
overloaded CPUs know about it. It increments the rto_loop_next. Then it
atomically sets rto_loop_start with a cmpxchg. If the old value is not "0",
then it is done, as another CPU is kicking off the IPI loop. If the old
value is "0", then it will take the rto_lock to synchronize with a possible
IPI being sent around to the overloaded CPUs.
If rto_cpu is greater than or equal to nr_cpu_ids, then there's either no
IPI being sent around, or one is about to finish. Then rto_cpu is set to the
first CPU in rto_mask and an IPI is sent to that CPU. If there's no CPUs set
in rto_mask, then there's nothing to be done.
When the CPU receives the IPI, it will first try to push any RT tasks that is
queued on the CPU but can't run because a higher priority RT task is
currently running on that CPU.
Then it takes the rto_lock and looks for the next CPU in the rto_mask. If it
finds one, it simply sends an IPI to that CPU and the process continues.
If there's no more CPUs in the rto_mask, then rto_loop is compared with
rto_loop_next. If they match, everything is done and the process is over. If
they do not match, then a CPU scheduled in a lower priority task as the IPI
was being passed around, and the process needs to start again. The first CPU
in rto_mask is sent the IPI.
This change removes this duplication of work in the IPI logic, and greatly
lowers the latency caused by the IPIs. This removed the lockup happening on
the 120 CPU machine. It also simplifies the code tremendously. What else
could anyone ask for?
Thanks to Peter Zijlstra for simplifying the rto_loop_start atomic logic and
supplying me with the rto_start_trylock() and rto_start_unlock() helper
functions.
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Clark Williams <williams@redhat.com>
Cc: Daniel Bristot de Oliveira <bristot@redhat.com>
Cc: John Kacur <jkacur@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Scott Wood <swood@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20170424114732.1aac6dc4@gandalf.local.home
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-10-06 18:05:04 +00:00
|
|
|
int next;
|
sched/rt: Use IPI to trigger RT task push migration instead of pulling
When debugging the latencies on a 40 core box, where we hit 300 to
500 microsecond latencies, I found there was a huge contention on the
runqueue locks.
Investigating it further, running ftrace, I found that it was due to
the pulling of RT tasks.
The test that was run was the following:
cyclictest --numa -p95 -m -d0 -i100
This created a thread on each CPU, that would set its wakeup in iterations
of 100 microseconds. The -d0 means that all the threads had the same
interval (100us). Each thread sleeps for 100us and wakes up and measures
its latencies.
cyclictest is maintained at:
git://git.kernel.org/pub/scm/linux/kernel/git/clrkwllms/rt-tests.git
What happened was another RT task would be scheduled on one of the CPUs
that was running our test, when the other CPU tests went to sleep and
scheduled idle. This caused the "pull" operation to execute on all
these CPUs. Each one of these saw the RT task that was overloaded on
the CPU of the test that was still running, and each one tried
to grab that task in a thundering herd way.
To grab the task, each thread would do a double rq lock grab, grabbing
its own lock as well as the rq of the overloaded CPU. As the sched
domains on this box was rather flat for its size, I saw up to 12 CPUs
block on this lock at once. This caused a ripple affect with the
rq locks especially since the taking was done via a double rq lock, which
means that several of the CPUs had their own rq locks held while trying
to take this rq lock. As these locks were blocked, any wakeups or load
balanceing on these CPUs would also block on these locks, and the wait
time escalated.
I've tried various methods to lessen the load, but things like an
atomic counter to only let one CPU grab the task wont work, because
the task may have a limited affinity, and we may pick the wrong
CPU to take that lock and do the pull, to only find out that the
CPU we picked isn't in the task's affinity.
Instead of doing the PULL, I now have the CPUs that want the pull to
send over an IPI to the overloaded CPU, and let that CPU pick what
CPU to push the task to. No more need to grab the rq lock, and the
push/pull algorithm still works fine.
With this patch, the latency dropped to just 150us over a 20 hour run.
Without the patch, the huge latencies would trigger in seconds.
I've created a new sched feature called RT_PUSH_IPI, which is enabled
by default.
When RT_PUSH_IPI is not enabled, the old method of grabbing the rq locks
and having the pulling CPU do the work is implemented. When RT_PUSH_IPI
is enabled, the IPI is sent to the overloaded CPU to do a push.
To enabled or disable this at run time:
# mount -t debugfs nodev /sys/kernel/debug
# echo RT_PUSH_IPI > /sys/kernel/debug/sched_features
or
# echo NO_RT_PUSH_IPI > /sys/kernel/debug/sched_features
Update: This original patch would send an IPI to all CPUs in the RT overload
list. But that could theoretically cause the reverse issue. That is, there
could be lots of overloaded RT queues and one CPU lowers its priority. It would
then send an IPI to all the overloaded RT queues and they could then all try
to grab the rq lock of the CPU lowering its priority, and then we have the
same problem.
The latest design sends out only one IPI to the first overloaded CPU. It tries to
push any tasks that it can, and then looks for the next overloaded CPU that can
push to the source CPU. The IPIs stop when all overloaded CPUs that have pushable
tasks that have priorities greater than the source CPU are covered. In case the
source CPU lowers its priority again, a flag is set to tell the IPI traversal to
restart with the first RT overloaded CPU after the source CPU.
Parts-suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Joern Engel <joern@purestorage.com>
Cc: Clark Williams <williams@redhat.com>
Cc: Mike Galbraith <umgwanakikbuti@gmail.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20150318144946.2f3cc982@gandalf.local.home
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2015-03-18 18:49:46 +00:00
|
|
|
int cpu;
|
|
|
|
|
|
|
|
/*
|
sched/rt: Simplify the IPI based RT balancing logic
When a CPU lowers its priority (schedules out a high priority task for a
lower priority one), a check is made to see if any other CPU has overloaded
RT tasks (more than one). It checks the rto_mask to determine this and if so
it will request to pull one of those tasks to itself if the non running RT
task is of higher priority than the new priority of the next task to run on
the current CPU.
When we deal with large number of CPUs, the original pull logic suffered
from large lock contention on a single CPU run queue, which caused a huge
latency across all CPUs. This was caused by only having one CPU having
overloaded RT tasks and a bunch of other CPUs lowering their priority. To
solve this issue, commit:
b6366f048e0c ("sched/rt: Use IPI to trigger RT task push migration instead of pulling")
changed the way to request a pull. Instead of grabbing the lock of the
overloaded CPU's runqueue, it simply sent an IPI to that CPU to do the work.
Although the IPI logic worked very well in removing the large latency build
up, it still could suffer from a large number of IPIs being sent to a single
CPU. On a 80 CPU box, I measured over 200us of processing IPIs. Worse yet,
when I tested this on a 120 CPU box, with a stress test that had lots of
RT tasks scheduling on all CPUs, it actually triggered the hard lockup
detector! One CPU had so many IPIs sent to it, and due to the restart
mechanism that is triggered when the source run queue has a priority status
change, the CPU spent minutes! processing the IPIs.
Thinking about this further, I realized there's no reason for each run queue
to send its own IPI. As all CPUs with overloaded tasks must be scanned
regardless if there's one or many CPUs lowering their priority, because
there's no current way to find the CPU with the highest priority task that
can schedule to one of these CPUs, there really only needs to be one IPI
being sent around at a time.
This greatly simplifies the code!
The new approach is to have each root domain have its own irq work, as the
rto_mask is per root domain. The root domain has the following fields
attached to it:
rto_push_work - the irq work to process each CPU set in rto_mask
rto_lock - the lock to protect some of the other rto fields
rto_loop_start - an atomic that keeps contention down on rto_lock
the first CPU scheduling in a lower priority task
is the one to kick off the process.
rto_loop_next - an atomic that gets incremented for each CPU that
schedules in a lower priority task.
rto_loop - a variable protected by rto_lock that is used to
compare against rto_loop_next
rto_cpu - The cpu to send the next IPI to, also protected by
the rto_lock.
When a CPU schedules in a lower priority task and wants to make sure
overloaded CPUs know about it. It increments the rto_loop_next. Then it
atomically sets rto_loop_start with a cmpxchg. If the old value is not "0",
then it is done, as another CPU is kicking off the IPI loop. If the old
value is "0", then it will take the rto_lock to synchronize with a possible
IPI being sent around to the overloaded CPUs.
If rto_cpu is greater than or equal to nr_cpu_ids, then there's either no
IPI being sent around, or one is about to finish. Then rto_cpu is set to the
first CPU in rto_mask and an IPI is sent to that CPU. If there's no CPUs set
in rto_mask, then there's nothing to be done.
When the CPU receives the IPI, it will first try to push any RT tasks that is
queued on the CPU but can't run because a higher priority RT task is
currently running on that CPU.
Then it takes the rto_lock and looks for the next CPU in the rto_mask. If it
finds one, it simply sends an IPI to that CPU and the process continues.
If there's no more CPUs in the rto_mask, then rto_loop is compared with
rto_loop_next. If they match, everything is done and the process is over. If
they do not match, then a CPU scheduled in a lower priority task as the IPI
was being passed around, and the process needs to start again. The first CPU
in rto_mask is sent the IPI.
This change removes this duplication of work in the IPI logic, and greatly
lowers the latency caused by the IPIs. This removed the lockup happening on
the 120 CPU machine. It also simplifies the code tremendously. What else
could anyone ask for?
Thanks to Peter Zijlstra for simplifying the rto_loop_start atomic logic and
supplying me with the rto_start_trylock() and rto_start_unlock() helper
functions.
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Clark Williams <williams@redhat.com>
Cc: Daniel Bristot de Oliveira <bristot@redhat.com>
Cc: John Kacur <jkacur@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Scott Wood <swood@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20170424114732.1aac6dc4@gandalf.local.home
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-10-06 18:05:04 +00:00
|
|
|
* When starting the IPI RT pushing, the rto_cpu is set to -1,
|
|
|
|
* rt_next_cpu() will simply return the first CPU found in
|
|
|
|
* the rto_mask.
|
|
|
|
*
|
sched: Clean up and harmonize the coding style of the scheduler code base
A good number of small style inconsistencies have accumulated
in the scheduler core, so do a pass over them to harmonize
all these details:
- fix speling in comments,
- use curly braces for multi-line statements,
- remove unnecessary parentheses from integer literals,
- capitalize consistently,
- remove stray newlines,
- add comments where necessary,
- remove invalid/unnecessary comments,
- align structure definitions and other data types vertically,
- add missing newlines for increased readability,
- fix vertical tabulation where it's misaligned,
- harmonize preprocessor conditional block labeling
and vertical alignment,
- remove line-breaks where they uglify the code,
- add newline after local variable definitions,
No change in functionality:
md5:
1191fa0a890cfa8132156d2959d7e9e2 built-in.o.before.asm
1191fa0a890cfa8132156d2959d7e9e2 built-in.o.after.asm
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-03-03 13:01:12 +00:00
|
|
|
* If rto_next_cpu() is called with rto_cpu is a valid CPU, it
|
sched/rt: Simplify the IPI based RT balancing logic
When a CPU lowers its priority (schedules out a high priority task for a
lower priority one), a check is made to see if any other CPU has overloaded
RT tasks (more than one). It checks the rto_mask to determine this and if so
it will request to pull one of those tasks to itself if the non running RT
task is of higher priority than the new priority of the next task to run on
the current CPU.
When we deal with large number of CPUs, the original pull logic suffered
from large lock contention on a single CPU run queue, which caused a huge
latency across all CPUs. This was caused by only having one CPU having
overloaded RT tasks and a bunch of other CPUs lowering their priority. To
solve this issue, commit:
b6366f048e0c ("sched/rt: Use IPI to trigger RT task push migration instead of pulling")
changed the way to request a pull. Instead of grabbing the lock of the
overloaded CPU's runqueue, it simply sent an IPI to that CPU to do the work.
Although the IPI logic worked very well in removing the large latency build
up, it still could suffer from a large number of IPIs being sent to a single
CPU. On a 80 CPU box, I measured over 200us of processing IPIs. Worse yet,
when I tested this on a 120 CPU box, with a stress test that had lots of
RT tasks scheduling on all CPUs, it actually triggered the hard lockup
detector! One CPU had so many IPIs sent to it, and due to the restart
mechanism that is triggered when the source run queue has a priority status
change, the CPU spent minutes! processing the IPIs.
Thinking about this further, I realized there's no reason for each run queue
to send its own IPI. As all CPUs with overloaded tasks must be scanned
regardless if there's one or many CPUs lowering their priority, because
there's no current way to find the CPU with the highest priority task that
can schedule to one of these CPUs, there really only needs to be one IPI
being sent around at a time.
This greatly simplifies the code!
The new approach is to have each root domain have its own irq work, as the
rto_mask is per root domain. The root domain has the following fields
attached to it:
rto_push_work - the irq work to process each CPU set in rto_mask
rto_lock - the lock to protect some of the other rto fields
rto_loop_start - an atomic that keeps contention down on rto_lock
the first CPU scheduling in a lower priority task
is the one to kick off the process.
rto_loop_next - an atomic that gets incremented for each CPU that
schedules in a lower priority task.
rto_loop - a variable protected by rto_lock that is used to
compare against rto_loop_next
rto_cpu - The cpu to send the next IPI to, also protected by
the rto_lock.
When a CPU schedules in a lower priority task and wants to make sure
overloaded CPUs know about it. It increments the rto_loop_next. Then it
atomically sets rto_loop_start with a cmpxchg. If the old value is not "0",
then it is done, as another CPU is kicking off the IPI loop. If the old
value is "0", then it will take the rto_lock to synchronize with a possible
IPI being sent around to the overloaded CPUs.
If rto_cpu is greater than or equal to nr_cpu_ids, then there's either no
IPI being sent around, or one is about to finish. Then rto_cpu is set to the
first CPU in rto_mask and an IPI is sent to that CPU. If there's no CPUs set
in rto_mask, then there's nothing to be done.
When the CPU receives the IPI, it will first try to push any RT tasks that is
queued on the CPU but can't run because a higher priority RT task is
currently running on that CPU.
Then it takes the rto_lock and looks for the next CPU in the rto_mask. If it
finds one, it simply sends an IPI to that CPU and the process continues.
If there's no more CPUs in the rto_mask, then rto_loop is compared with
rto_loop_next. If they match, everything is done and the process is over. If
they do not match, then a CPU scheduled in a lower priority task as the IPI
was being passed around, and the process needs to start again. The first CPU
in rto_mask is sent the IPI.
This change removes this duplication of work in the IPI logic, and greatly
lowers the latency caused by the IPIs. This removed the lockup happening on
the 120 CPU machine. It also simplifies the code tremendously. What else
could anyone ask for?
Thanks to Peter Zijlstra for simplifying the rto_loop_start atomic logic and
supplying me with the rto_start_trylock() and rto_start_unlock() helper
functions.
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Clark Williams <williams@redhat.com>
Cc: Daniel Bristot de Oliveira <bristot@redhat.com>
Cc: John Kacur <jkacur@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Scott Wood <swood@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20170424114732.1aac6dc4@gandalf.local.home
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-10-06 18:05:04 +00:00
|
|
|
* will return the next CPU found in the rto_mask.
|
|
|
|
*
|
|
|
|
* If there are no more CPUs left in the rto_mask, then a check is made
|
|
|
|
* against rto_loop and rto_loop_next. rto_loop is only updated with
|
|
|
|
* the rto_lock held, but any CPU may increment the rto_loop_next
|
|
|
|
* without any locking.
|
sched/rt: Use IPI to trigger RT task push migration instead of pulling
When debugging the latencies on a 40 core box, where we hit 300 to
500 microsecond latencies, I found there was a huge contention on the
runqueue locks.
Investigating it further, running ftrace, I found that it was due to
the pulling of RT tasks.
The test that was run was the following:
cyclictest --numa -p95 -m -d0 -i100
This created a thread on each CPU, that would set its wakeup in iterations
of 100 microseconds. The -d0 means that all the threads had the same
interval (100us). Each thread sleeps for 100us and wakes up and measures
its latencies.
cyclictest is maintained at:
git://git.kernel.org/pub/scm/linux/kernel/git/clrkwllms/rt-tests.git
What happened was another RT task would be scheduled on one of the CPUs
that was running our test, when the other CPU tests went to sleep and
scheduled idle. This caused the "pull" operation to execute on all
these CPUs. Each one of these saw the RT task that was overloaded on
the CPU of the test that was still running, and each one tried
to grab that task in a thundering herd way.
To grab the task, each thread would do a double rq lock grab, grabbing
its own lock as well as the rq of the overloaded CPU. As the sched
domains on this box was rather flat for its size, I saw up to 12 CPUs
block on this lock at once. This caused a ripple affect with the
rq locks especially since the taking was done via a double rq lock, which
means that several of the CPUs had their own rq locks held while trying
to take this rq lock. As these locks were blocked, any wakeups or load
balanceing on these CPUs would also block on these locks, and the wait
time escalated.
I've tried various methods to lessen the load, but things like an
atomic counter to only let one CPU grab the task wont work, because
the task may have a limited affinity, and we may pick the wrong
CPU to take that lock and do the pull, to only find out that the
CPU we picked isn't in the task's affinity.
Instead of doing the PULL, I now have the CPUs that want the pull to
send over an IPI to the overloaded CPU, and let that CPU pick what
CPU to push the task to. No more need to grab the rq lock, and the
push/pull algorithm still works fine.
With this patch, the latency dropped to just 150us over a 20 hour run.
Without the patch, the huge latencies would trigger in seconds.
I've created a new sched feature called RT_PUSH_IPI, which is enabled
by default.
When RT_PUSH_IPI is not enabled, the old method of grabbing the rq locks
and having the pulling CPU do the work is implemented. When RT_PUSH_IPI
is enabled, the IPI is sent to the overloaded CPU to do a push.
To enabled or disable this at run time:
# mount -t debugfs nodev /sys/kernel/debug
# echo RT_PUSH_IPI > /sys/kernel/debug/sched_features
or
# echo NO_RT_PUSH_IPI > /sys/kernel/debug/sched_features
Update: This original patch would send an IPI to all CPUs in the RT overload
list. But that could theoretically cause the reverse issue. That is, there
could be lots of overloaded RT queues and one CPU lowers its priority. It would
then send an IPI to all the overloaded RT queues and they could then all try
to grab the rq lock of the CPU lowering its priority, and then we have the
same problem.
The latest design sends out only one IPI to the first overloaded CPU. It tries to
push any tasks that it can, and then looks for the next overloaded CPU that can
push to the source CPU. The IPIs stop when all overloaded CPUs that have pushable
tasks that have priorities greater than the source CPU are covered. In case the
source CPU lowers its priority again, a flag is set to tell the IPI traversal to
restart with the first RT overloaded CPU after the source CPU.
Parts-suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Joern Engel <joern@purestorage.com>
Cc: Clark Williams <williams@redhat.com>
Cc: Mike Galbraith <umgwanakikbuti@gmail.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20150318144946.2f3cc982@gandalf.local.home
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2015-03-18 18:49:46 +00:00
|
|
|
*/
|
sched/rt: Simplify the IPI based RT balancing logic
When a CPU lowers its priority (schedules out a high priority task for a
lower priority one), a check is made to see if any other CPU has overloaded
RT tasks (more than one). It checks the rto_mask to determine this and if so
it will request to pull one of those tasks to itself if the non running RT
task is of higher priority than the new priority of the next task to run on
the current CPU.
When we deal with large number of CPUs, the original pull logic suffered
from large lock contention on a single CPU run queue, which caused a huge
latency across all CPUs. This was caused by only having one CPU having
overloaded RT tasks and a bunch of other CPUs lowering their priority. To
solve this issue, commit:
b6366f048e0c ("sched/rt: Use IPI to trigger RT task push migration instead of pulling")
changed the way to request a pull. Instead of grabbing the lock of the
overloaded CPU's runqueue, it simply sent an IPI to that CPU to do the work.
Although the IPI logic worked very well in removing the large latency build
up, it still could suffer from a large number of IPIs being sent to a single
CPU. On a 80 CPU box, I measured over 200us of processing IPIs. Worse yet,
when I tested this on a 120 CPU box, with a stress test that had lots of
RT tasks scheduling on all CPUs, it actually triggered the hard lockup
detector! One CPU had so many IPIs sent to it, and due to the restart
mechanism that is triggered when the source run queue has a priority status
change, the CPU spent minutes! processing the IPIs.
Thinking about this further, I realized there's no reason for each run queue
to send its own IPI. As all CPUs with overloaded tasks must be scanned
regardless if there's one or many CPUs lowering their priority, because
there's no current way to find the CPU with the highest priority task that
can schedule to one of these CPUs, there really only needs to be one IPI
being sent around at a time.
This greatly simplifies the code!
The new approach is to have each root domain have its own irq work, as the
rto_mask is per root domain. The root domain has the following fields
attached to it:
rto_push_work - the irq work to process each CPU set in rto_mask
rto_lock - the lock to protect some of the other rto fields
rto_loop_start - an atomic that keeps contention down on rto_lock
the first CPU scheduling in a lower priority task
is the one to kick off the process.
rto_loop_next - an atomic that gets incremented for each CPU that
schedules in a lower priority task.
rto_loop - a variable protected by rto_lock that is used to
compare against rto_loop_next
rto_cpu - The cpu to send the next IPI to, also protected by
the rto_lock.
When a CPU schedules in a lower priority task and wants to make sure
overloaded CPUs know about it. It increments the rto_loop_next. Then it
atomically sets rto_loop_start with a cmpxchg. If the old value is not "0",
then it is done, as another CPU is kicking off the IPI loop. If the old
value is "0", then it will take the rto_lock to synchronize with a possible
IPI being sent around to the overloaded CPUs.
If rto_cpu is greater than or equal to nr_cpu_ids, then there's either no
IPI being sent around, or one is about to finish. Then rto_cpu is set to the
first CPU in rto_mask and an IPI is sent to that CPU. If there's no CPUs set
in rto_mask, then there's nothing to be done.
When the CPU receives the IPI, it will first try to push any RT tasks that is
queued on the CPU but can't run because a higher priority RT task is
currently running on that CPU.
Then it takes the rto_lock and looks for the next CPU in the rto_mask. If it
finds one, it simply sends an IPI to that CPU and the process continues.
If there's no more CPUs in the rto_mask, then rto_loop is compared with
rto_loop_next. If they match, everything is done and the process is over. If
they do not match, then a CPU scheduled in a lower priority task as the IPI
was being passed around, and the process needs to start again. The first CPU
in rto_mask is sent the IPI.
This change removes this duplication of work in the IPI logic, and greatly
lowers the latency caused by the IPIs. This removed the lockup happening on
the 120 CPU machine. It also simplifies the code tremendously. What else
could anyone ask for?
Thanks to Peter Zijlstra for simplifying the rto_loop_start atomic logic and
supplying me with the rto_start_trylock() and rto_start_unlock() helper
functions.
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Clark Williams <williams@redhat.com>
Cc: Daniel Bristot de Oliveira <bristot@redhat.com>
Cc: John Kacur <jkacur@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Scott Wood <swood@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20170424114732.1aac6dc4@gandalf.local.home
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-10-06 18:05:04 +00:00
|
|
|
for (;;) {
|
sched/rt: Use IPI to trigger RT task push migration instead of pulling
When debugging the latencies on a 40 core box, where we hit 300 to
500 microsecond latencies, I found there was a huge contention on the
runqueue locks.
Investigating it further, running ftrace, I found that it was due to
the pulling of RT tasks.
The test that was run was the following:
cyclictest --numa -p95 -m -d0 -i100
This created a thread on each CPU, that would set its wakeup in iterations
of 100 microseconds. The -d0 means that all the threads had the same
interval (100us). Each thread sleeps for 100us and wakes up and measures
its latencies.
cyclictest is maintained at:
git://git.kernel.org/pub/scm/linux/kernel/git/clrkwllms/rt-tests.git
What happened was another RT task would be scheduled on one of the CPUs
that was running our test, when the other CPU tests went to sleep and
scheduled idle. This caused the "pull" operation to execute on all
these CPUs. Each one of these saw the RT task that was overloaded on
the CPU of the test that was still running, and each one tried
to grab that task in a thundering herd way.
To grab the task, each thread would do a double rq lock grab, grabbing
its own lock as well as the rq of the overloaded CPU. As the sched
domains on this box was rather flat for its size, I saw up to 12 CPUs
block on this lock at once. This caused a ripple affect with the
rq locks especially since the taking was done via a double rq lock, which
means that several of the CPUs had their own rq locks held while trying
to take this rq lock. As these locks were blocked, any wakeups or load
balanceing on these CPUs would also block on these locks, and the wait
time escalated.
I've tried various methods to lessen the load, but things like an
atomic counter to only let one CPU grab the task wont work, because
the task may have a limited affinity, and we may pick the wrong
CPU to take that lock and do the pull, to only find out that the
CPU we picked isn't in the task's affinity.
Instead of doing the PULL, I now have the CPUs that want the pull to
send over an IPI to the overloaded CPU, and let that CPU pick what
CPU to push the task to. No more need to grab the rq lock, and the
push/pull algorithm still works fine.
With this patch, the latency dropped to just 150us over a 20 hour run.
Without the patch, the huge latencies would trigger in seconds.
I've created a new sched feature called RT_PUSH_IPI, which is enabled
by default.
When RT_PUSH_IPI is not enabled, the old method of grabbing the rq locks
and having the pulling CPU do the work is implemented. When RT_PUSH_IPI
is enabled, the IPI is sent to the overloaded CPU to do a push.
To enabled or disable this at run time:
# mount -t debugfs nodev /sys/kernel/debug
# echo RT_PUSH_IPI > /sys/kernel/debug/sched_features
or
# echo NO_RT_PUSH_IPI > /sys/kernel/debug/sched_features
Update: This original patch would send an IPI to all CPUs in the RT overload
list. But that could theoretically cause the reverse issue. That is, there
could be lots of overloaded RT queues and one CPU lowers its priority. It would
then send an IPI to all the overloaded RT queues and they could then all try
to grab the rq lock of the CPU lowering its priority, and then we have the
same problem.
The latest design sends out only one IPI to the first overloaded CPU. It tries to
push any tasks that it can, and then looks for the next overloaded CPU that can
push to the source CPU. The IPIs stop when all overloaded CPUs that have pushable
tasks that have priorities greater than the source CPU are covered. In case the
source CPU lowers its priority again, a flag is set to tell the IPI traversal to
restart with the first RT overloaded CPU after the source CPU.
Parts-suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Joern Engel <joern@purestorage.com>
Cc: Clark Williams <williams@redhat.com>
Cc: Mike Galbraith <umgwanakikbuti@gmail.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20150318144946.2f3cc982@gandalf.local.home
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2015-03-18 18:49:46 +00:00
|
|
|
|
sched/rt: Simplify the IPI based RT balancing logic
When a CPU lowers its priority (schedules out a high priority task for a
lower priority one), a check is made to see if any other CPU has overloaded
RT tasks (more than one). It checks the rto_mask to determine this and if so
it will request to pull one of those tasks to itself if the non running RT
task is of higher priority than the new priority of the next task to run on
the current CPU.
When we deal with large number of CPUs, the original pull logic suffered
from large lock contention on a single CPU run queue, which caused a huge
latency across all CPUs. This was caused by only having one CPU having
overloaded RT tasks and a bunch of other CPUs lowering their priority. To
solve this issue, commit:
b6366f048e0c ("sched/rt: Use IPI to trigger RT task push migration instead of pulling")
changed the way to request a pull. Instead of grabbing the lock of the
overloaded CPU's runqueue, it simply sent an IPI to that CPU to do the work.
Although the IPI logic worked very well in removing the large latency build
up, it still could suffer from a large number of IPIs being sent to a single
CPU. On a 80 CPU box, I measured over 200us of processing IPIs. Worse yet,
when I tested this on a 120 CPU box, with a stress test that had lots of
RT tasks scheduling on all CPUs, it actually triggered the hard lockup
detector! One CPU had so many IPIs sent to it, and due to the restart
mechanism that is triggered when the source run queue has a priority status
change, the CPU spent minutes! processing the IPIs.
Thinking about this further, I realized there's no reason for each run queue
to send its own IPI. As all CPUs with overloaded tasks must be scanned
regardless if there's one or many CPUs lowering their priority, because
there's no current way to find the CPU with the highest priority task that
can schedule to one of these CPUs, there really only needs to be one IPI
being sent around at a time.
This greatly simplifies the code!
The new approach is to have each root domain have its own irq work, as the
rto_mask is per root domain. The root domain has the following fields
attached to it:
rto_push_work - the irq work to process each CPU set in rto_mask
rto_lock - the lock to protect some of the other rto fields
rto_loop_start - an atomic that keeps contention down on rto_lock
the first CPU scheduling in a lower priority task
is the one to kick off the process.
rto_loop_next - an atomic that gets incremented for each CPU that
schedules in a lower priority task.
rto_loop - a variable protected by rto_lock that is used to
compare against rto_loop_next
rto_cpu - The cpu to send the next IPI to, also protected by
the rto_lock.
When a CPU schedules in a lower priority task and wants to make sure
overloaded CPUs know about it. It increments the rto_loop_next. Then it
atomically sets rto_loop_start with a cmpxchg. If the old value is not "0",
then it is done, as another CPU is kicking off the IPI loop. If the old
value is "0", then it will take the rto_lock to synchronize with a possible
IPI being sent around to the overloaded CPUs.
If rto_cpu is greater than or equal to nr_cpu_ids, then there's either no
IPI being sent around, or one is about to finish. Then rto_cpu is set to the
first CPU in rto_mask and an IPI is sent to that CPU. If there's no CPUs set
in rto_mask, then there's nothing to be done.
When the CPU receives the IPI, it will first try to push any RT tasks that is
queued on the CPU but can't run because a higher priority RT task is
currently running on that CPU.
Then it takes the rto_lock and looks for the next CPU in the rto_mask. If it
finds one, it simply sends an IPI to that CPU and the process continues.
If there's no more CPUs in the rto_mask, then rto_loop is compared with
rto_loop_next. If they match, everything is done and the process is over. If
they do not match, then a CPU scheduled in a lower priority task as the IPI
was being passed around, and the process needs to start again. The first CPU
in rto_mask is sent the IPI.
This change removes this duplication of work in the IPI logic, and greatly
lowers the latency caused by the IPIs. This removed the lockup happening on
the 120 CPU machine. It also simplifies the code tremendously. What else
could anyone ask for?
Thanks to Peter Zijlstra for simplifying the rto_loop_start atomic logic and
supplying me with the rto_start_trylock() and rto_start_unlock() helper
functions.
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Clark Williams <williams@redhat.com>
Cc: Daniel Bristot de Oliveira <bristot@redhat.com>
Cc: John Kacur <jkacur@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Scott Wood <swood@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20170424114732.1aac6dc4@gandalf.local.home
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-10-06 18:05:04 +00:00
|
|
|
/* When rto_cpu is -1 this acts like cpumask_first() */
|
|
|
|
cpu = cpumask_next(rd->rto_cpu, rd->rto_mask);
|
sched/rt: Use IPI to trigger RT task push migration instead of pulling
When debugging the latencies on a 40 core box, where we hit 300 to
500 microsecond latencies, I found there was a huge contention on the
runqueue locks.
Investigating it further, running ftrace, I found that it was due to
the pulling of RT tasks.
The test that was run was the following:
cyclictest --numa -p95 -m -d0 -i100
This created a thread on each CPU, that would set its wakeup in iterations
of 100 microseconds. The -d0 means that all the threads had the same
interval (100us). Each thread sleeps for 100us and wakes up and measures
its latencies.
cyclictest is maintained at:
git://git.kernel.org/pub/scm/linux/kernel/git/clrkwllms/rt-tests.git
What happened was another RT task would be scheduled on one of the CPUs
that was running our test, when the other CPU tests went to sleep and
scheduled idle. This caused the "pull" operation to execute on all
these CPUs. Each one of these saw the RT task that was overloaded on
the CPU of the test that was still running, and each one tried
to grab that task in a thundering herd way.
To grab the task, each thread would do a double rq lock grab, grabbing
its own lock as well as the rq of the overloaded CPU. As the sched
domains on this box was rather flat for its size, I saw up to 12 CPUs
block on this lock at once. This caused a ripple affect with the
rq locks especially since the taking was done via a double rq lock, which
means that several of the CPUs had their own rq locks held while trying
to take this rq lock. As these locks were blocked, any wakeups or load
balanceing on these CPUs would also block on these locks, and the wait
time escalated.
I've tried various methods to lessen the load, but things like an
atomic counter to only let one CPU grab the task wont work, because
the task may have a limited affinity, and we may pick the wrong
CPU to take that lock and do the pull, to only find out that the
CPU we picked isn't in the task's affinity.
Instead of doing the PULL, I now have the CPUs that want the pull to
send over an IPI to the overloaded CPU, and let that CPU pick what
CPU to push the task to. No more need to grab the rq lock, and the
push/pull algorithm still works fine.
With this patch, the latency dropped to just 150us over a 20 hour run.
Without the patch, the huge latencies would trigger in seconds.
I've created a new sched feature called RT_PUSH_IPI, which is enabled
by default.
When RT_PUSH_IPI is not enabled, the old method of grabbing the rq locks
and having the pulling CPU do the work is implemented. When RT_PUSH_IPI
is enabled, the IPI is sent to the overloaded CPU to do a push.
To enabled or disable this at run time:
# mount -t debugfs nodev /sys/kernel/debug
# echo RT_PUSH_IPI > /sys/kernel/debug/sched_features
or
# echo NO_RT_PUSH_IPI > /sys/kernel/debug/sched_features
Update: This original patch would send an IPI to all CPUs in the RT overload
list. But that could theoretically cause the reverse issue. That is, there
could be lots of overloaded RT queues and one CPU lowers its priority. It would
then send an IPI to all the overloaded RT queues and they could then all try
to grab the rq lock of the CPU lowering its priority, and then we have the
same problem.
The latest design sends out only one IPI to the first overloaded CPU. It tries to
push any tasks that it can, and then looks for the next overloaded CPU that can
push to the source CPU. The IPIs stop when all overloaded CPUs that have pushable
tasks that have priorities greater than the source CPU are covered. In case the
source CPU lowers its priority again, a flag is set to tell the IPI traversal to
restart with the first RT overloaded CPU after the source CPU.
Parts-suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Joern Engel <joern@purestorage.com>
Cc: Clark Williams <williams@redhat.com>
Cc: Mike Galbraith <umgwanakikbuti@gmail.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20150318144946.2f3cc982@gandalf.local.home
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2015-03-18 18:49:46 +00:00
|
|
|
|
sched/rt: Simplify the IPI based RT balancing logic
When a CPU lowers its priority (schedules out a high priority task for a
lower priority one), a check is made to see if any other CPU has overloaded
RT tasks (more than one). It checks the rto_mask to determine this and if so
it will request to pull one of those tasks to itself if the non running RT
task is of higher priority than the new priority of the next task to run on
the current CPU.
When we deal with large number of CPUs, the original pull logic suffered
from large lock contention on a single CPU run queue, which caused a huge
latency across all CPUs. This was caused by only having one CPU having
overloaded RT tasks and a bunch of other CPUs lowering their priority. To
solve this issue, commit:
b6366f048e0c ("sched/rt: Use IPI to trigger RT task push migration instead of pulling")
changed the way to request a pull. Instead of grabbing the lock of the
overloaded CPU's runqueue, it simply sent an IPI to that CPU to do the work.
Although the IPI logic worked very well in removing the large latency build
up, it still could suffer from a large number of IPIs being sent to a single
CPU. On a 80 CPU box, I measured over 200us of processing IPIs. Worse yet,
when I tested this on a 120 CPU box, with a stress test that had lots of
RT tasks scheduling on all CPUs, it actually triggered the hard lockup
detector! One CPU had so many IPIs sent to it, and due to the restart
mechanism that is triggered when the source run queue has a priority status
change, the CPU spent minutes! processing the IPIs.
Thinking about this further, I realized there's no reason for each run queue
to send its own IPI. As all CPUs with overloaded tasks must be scanned
regardless if there's one or many CPUs lowering their priority, because
there's no current way to find the CPU with the highest priority task that
can schedule to one of these CPUs, there really only needs to be one IPI
being sent around at a time.
This greatly simplifies the code!
The new approach is to have each root domain have its own irq work, as the
rto_mask is per root domain. The root domain has the following fields
attached to it:
rto_push_work - the irq work to process each CPU set in rto_mask
rto_lock - the lock to protect some of the other rto fields
rto_loop_start - an atomic that keeps contention down on rto_lock
the first CPU scheduling in a lower priority task
is the one to kick off the process.
rto_loop_next - an atomic that gets incremented for each CPU that
schedules in a lower priority task.
rto_loop - a variable protected by rto_lock that is used to
compare against rto_loop_next
rto_cpu - The cpu to send the next IPI to, also protected by
the rto_lock.
When a CPU schedules in a lower priority task and wants to make sure
overloaded CPUs know about it. It increments the rto_loop_next. Then it
atomically sets rto_loop_start with a cmpxchg. If the old value is not "0",
then it is done, as another CPU is kicking off the IPI loop. If the old
value is "0", then it will take the rto_lock to synchronize with a possible
IPI being sent around to the overloaded CPUs.
If rto_cpu is greater than or equal to nr_cpu_ids, then there's either no
IPI being sent around, or one is about to finish. Then rto_cpu is set to the
first CPU in rto_mask and an IPI is sent to that CPU. If there's no CPUs set
in rto_mask, then there's nothing to be done.
When the CPU receives the IPI, it will first try to push any RT tasks that is
queued on the CPU but can't run because a higher priority RT task is
currently running on that CPU.
Then it takes the rto_lock and looks for the next CPU in the rto_mask. If it
finds one, it simply sends an IPI to that CPU and the process continues.
If there's no more CPUs in the rto_mask, then rto_loop is compared with
rto_loop_next. If they match, everything is done and the process is over. If
they do not match, then a CPU scheduled in a lower priority task as the IPI
was being passed around, and the process needs to start again. The first CPU
in rto_mask is sent the IPI.
This change removes this duplication of work in the IPI logic, and greatly
lowers the latency caused by the IPIs. This removed the lockup happening on
the 120 CPU machine. It also simplifies the code tremendously. What else
could anyone ask for?
Thanks to Peter Zijlstra for simplifying the rto_loop_start atomic logic and
supplying me with the rto_start_trylock() and rto_start_unlock() helper
functions.
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Clark Williams <williams@redhat.com>
Cc: Daniel Bristot de Oliveira <bristot@redhat.com>
Cc: John Kacur <jkacur@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Scott Wood <swood@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20170424114732.1aac6dc4@gandalf.local.home
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-10-06 18:05:04 +00:00
|
|
|
rd->rto_cpu = cpu;
|
sched/rt: Use IPI to trigger RT task push migration instead of pulling
When debugging the latencies on a 40 core box, where we hit 300 to
500 microsecond latencies, I found there was a huge contention on the
runqueue locks.
Investigating it further, running ftrace, I found that it was due to
the pulling of RT tasks.
The test that was run was the following:
cyclictest --numa -p95 -m -d0 -i100
This created a thread on each CPU, that would set its wakeup in iterations
of 100 microseconds. The -d0 means that all the threads had the same
interval (100us). Each thread sleeps for 100us and wakes up and measures
its latencies.
cyclictest is maintained at:
git://git.kernel.org/pub/scm/linux/kernel/git/clrkwllms/rt-tests.git
What happened was another RT task would be scheduled on one of the CPUs
that was running our test, when the other CPU tests went to sleep and
scheduled idle. This caused the "pull" operation to execute on all
these CPUs. Each one of these saw the RT task that was overloaded on
the CPU of the test that was still running, and each one tried
to grab that task in a thundering herd way.
To grab the task, each thread would do a double rq lock grab, grabbing
its own lock as well as the rq of the overloaded CPU. As the sched
domains on this box was rather flat for its size, I saw up to 12 CPUs
block on this lock at once. This caused a ripple affect with the
rq locks especially since the taking was done via a double rq lock, which
means that several of the CPUs had their own rq locks held while trying
to take this rq lock. As these locks were blocked, any wakeups or load
balanceing on these CPUs would also block on these locks, and the wait
time escalated.
I've tried various methods to lessen the load, but things like an
atomic counter to only let one CPU grab the task wont work, because
the task may have a limited affinity, and we may pick the wrong
CPU to take that lock and do the pull, to only find out that the
CPU we picked isn't in the task's affinity.
Instead of doing the PULL, I now have the CPUs that want the pull to
send over an IPI to the overloaded CPU, and let that CPU pick what
CPU to push the task to. No more need to grab the rq lock, and the
push/pull algorithm still works fine.
With this patch, the latency dropped to just 150us over a 20 hour run.
Without the patch, the huge latencies would trigger in seconds.
I've created a new sched feature called RT_PUSH_IPI, which is enabled
by default.
When RT_PUSH_IPI is not enabled, the old method of grabbing the rq locks
and having the pulling CPU do the work is implemented. When RT_PUSH_IPI
is enabled, the IPI is sent to the overloaded CPU to do a push.
To enabled or disable this at run time:
# mount -t debugfs nodev /sys/kernel/debug
# echo RT_PUSH_IPI > /sys/kernel/debug/sched_features
or
# echo NO_RT_PUSH_IPI > /sys/kernel/debug/sched_features
Update: This original patch would send an IPI to all CPUs in the RT overload
list. But that could theoretically cause the reverse issue. That is, there
could be lots of overloaded RT queues and one CPU lowers its priority. It would
then send an IPI to all the overloaded RT queues and they could then all try
to grab the rq lock of the CPU lowering its priority, and then we have the
same problem.
The latest design sends out only one IPI to the first overloaded CPU. It tries to
push any tasks that it can, and then looks for the next overloaded CPU that can
push to the source CPU. The IPIs stop when all overloaded CPUs that have pushable
tasks that have priorities greater than the source CPU are covered. In case the
source CPU lowers its priority again, a flag is set to tell the IPI traversal to
restart with the first RT overloaded CPU after the source CPU.
Parts-suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Joern Engel <joern@purestorage.com>
Cc: Clark Williams <williams@redhat.com>
Cc: Mike Galbraith <umgwanakikbuti@gmail.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20150318144946.2f3cc982@gandalf.local.home
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2015-03-18 18:49:46 +00:00
|
|
|
|
sched/rt: Simplify the IPI based RT balancing logic
When a CPU lowers its priority (schedules out a high priority task for a
lower priority one), a check is made to see if any other CPU has overloaded
RT tasks (more than one). It checks the rto_mask to determine this and if so
it will request to pull one of those tasks to itself if the non running RT
task is of higher priority than the new priority of the next task to run on
the current CPU.
When we deal with large number of CPUs, the original pull logic suffered
from large lock contention on a single CPU run queue, which caused a huge
latency across all CPUs. This was caused by only having one CPU having
overloaded RT tasks and a bunch of other CPUs lowering their priority. To
solve this issue, commit:
b6366f048e0c ("sched/rt: Use IPI to trigger RT task push migration instead of pulling")
changed the way to request a pull. Instead of grabbing the lock of the
overloaded CPU's runqueue, it simply sent an IPI to that CPU to do the work.
Although the IPI logic worked very well in removing the large latency build
up, it still could suffer from a large number of IPIs being sent to a single
CPU. On a 80 CPU box, I measured over 200us of processing IPIs. Worse yet,
when I tested this on a 120 CPU box, with a stress test that had lots of
RT tasks scheduling on all CPUs, it actually triggered the hard lockup
detector! One CPU had so many IPIs sent to it, and due to the restart
mechanism that is triggered when the source run queue has a priority status
change, the CPU spent minutes! processing the IPIs.
Thinking about this further, I realized there's no reason for each run queue
to send its own IPI. As all CPUs with overloaded tasks must be scanned
regardless if there's one or many CPUs lowering their priority, because
there's no current way to find the CPU with the highest priority task that
can schedule to one of these CPUs, there really only needs to be one IPI
being sent around at a time.
This greatly simplifies the code!
The new approach is to have each root domain have its own irq work, as the
rto_mask is per root domain. The root domain has the following fields
attached to it:
rto_push_work - the irq work to process each CPU set in rto_mask
rto_lock - the lock to protect some of the other rto fields
rto_loop_start - an atomic that keeps contention down on rto_lock
the first CPU scheduling in a lower priority task
is the one to kick off the process.
rto_loop_next - an atomic that gets incremented for each CPU that
schedules in a lower priority task.
rto_loop - a variable protected by rto_lock that is used to
compare against rto_loop_next
rto_cpu - The cpu to send the next IPI to, also protected by
the rto_lock.
When a CPU schedules in a lower priority task and wants to make sure
overloaded CPUs know about it. It increments the rto_loop_next. Then it
atomically sets rto_loop_start with a cmpxchg. If the old value is not "0",
then it is done, as another CPU is kicking off the IPI loop. If the old
value is "0", then it will take the rto_lock to synchronize with a possible
IPI being sent around to the overloaded CPUs.
If rto_cpu is greater than or equal to nr_cpu_ids, then there's either no
IPI being sent around, or one is about to finish. Then rto_cpu is set to the
first CPU in rto_mask and an IPI is sent to that CPU. If there's no CPUs set
in rto_mask, then there's nothing to be done.
When the CPU receives the IPI, it will first try to push any RT tasks that is
queued on the CPU but can't run because a higher priority RT task is
currently running on that CPU.
Then it takes the rto_lock and looks for the next CPU in the rto_mask. If it
finds one, it simply sends an IPI to that CPU and the process continues.
If there's no more CPUs in the rto_mask, then rto_loop is compared with
rto_loop_next. If they match, everything is done and the process is over. If
they do not match, then a CPU scheduled in a lower priority task as the IPI
was being passed around, and the process needs to start again. The first CPU
in rto_mask is sent the IPI.
This change removes this duplication of work in the IPI logic, and greatly
lowers the latency caused by the IPIs. This removed the lockup happening on
the 120 CPU machine. It also simplifies the code tremendously. What else
could anyone ask for?
Thanks to Peter Zijlstra for simplifying the rto_loop_start atomic logic and
supplying me with the rto_start_trylock() and rto_start_unlock() helper
functions.
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Clark Williams <williams@redhat.com>
Cc: Daniel Bristot de Oliveira <bristot@redhat.com>
Cc: John Kacur <jkacur@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Scott Wood <swood@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20170424114732.1aac6dc4@gandalf.local.home
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-10-06 18:05:04 +00:00
|
|
|
if (cpu < nr_cpu_ids)
|
|
|
|
return cpu;
|
sched/rt: Use IPI to trigger RT task push migration instead of pulling
When debugging the latencies on a 40 core box, where we hit 300 to
500 microsecond latencies, I found there was a huge contention on the
runqueue locks.
Investigating it further, running ftrace, I found that it was due to
the pulling of RT tasks.
The test that was run was the following:
cyclictest --numa -p95 -m -d0 -i100
This created a thread on each CPU, that would set its wakeup in iterations
of 100 microseconds. The -d0 means that all the threads had the same
interval (100us). Each thread sleeps for 100us and wakes up and measures
its latencies.
cyclictest is maintained at:
git://git.kernel.org/pub/scm/linux/kernel/git/clrkwllms/rt-tests.git
What happened was another RT task would be scheduled on one of the CPUs
that was running our test, when the other CPU tests went to sleep and
scheduled idle. This caused the "pull" operation to execute on all
these CPUs. Each one of these saw the RT task that was overloaded on
the CPU of the test that was still running, and each one tried
to grab that task in a thundering herd way.
To grab the task, each thread would do a double rq lock grab, grabbing
its own lock as well as the rq of the overloaded CPU. As the sched
domains on this box was rather flat for its size, I saw up to 12 CPUs
block on this lock at once. This caused a ripple affect with the
rq locks especially since the taking was done via a double rq lock, which
means that several of the CPUs had their own rq locks held while trying
to take this rq lock. As these locks were blocked, any wakeups or load
balanceing on these CPUs would also block on these locks, and the wait
time escalated.
I've tried various methods to lessen the load, but things like an
atomic counter to only let one CPU grab the task wont work, because
the task may have a limited affinity, and we may pick the wrong
CPU to take that lock and do the pull, to only find out that the
CPU we picked isn't in the task's affinity.
Instead of doing the PULL, I now have the CPUs that want the pull to
send over an IPI to the overloaded CPU, and let that CPU pick what
CPU to push the task to. No more need to grab the rq lock, and the
push/pull algorithm still works fine.
With this patch, the latency dropped to just 150us over a 20 hour run.
Without the patch, the huge latencies would trigger in seconds.
I've created a new sched feature called RT_PUSH_IPI, which is enabled
by default.
When RT_PUSH_IPI is not enabled, the old method of grabbing the rq locks
and having the pulling CPU do the work is implemented. When RT_PUSH_IPI
is enabled, the IPI is sent to the overloaded CPU to do a push.
To enabled or disable this at run time:
# mount -t debugfs nodev /sys/kernel/debug
# echo RT_PUSH_IPI > /sys/kernel/debug/sched_features
or
# echo NO_RT_PUSH_IPI > /sys/kernel/debug/sched_features
Update: This original patch would send an IPI to all CPUs in the RT overload
list. But that could theoretically cause the reverse issue. That is, there
could be lots of overloaded RT queues and one CPU lowers its priority. It would
then send an IPI to all the overloaded RT queues and they could then all try
to grab the rq lock of the CPU lowering its priority, and then we have the
same problem.
The latest design sends out only one IPI to the first overloaded CPU. It tries to
push any tasks that it can, and then looks for the next overloaded CPU that can
push to the source CPU. The IPIs stop when all overloaded CPUs that have pushable
tasks that have priorities greater than the source CPU are covered. In case the
source CPU lowers its priority again, a flag is set to tell the IPI traversal to
restart with the first RT overloaded CPU after the source CPU.
Parts-suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Joern Engel <joern@purestorage.com>
Cc: Clark Williams <williams@redhat.com>
Cc: Mike Galbraith <umgwanakikbuti@gmail.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20150318144946.2f3cc982@gandalf.local.home
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2015-03-18 18:49:46 +00:00
|
|
|
|
sched/rt: Simplify the IPI based RT balancing logic
When a CPU lowers its priority (schedules out a high priority task for a
lower priority one), a check is made to see if any other CPU has overloaded
RT tasks (more than one). It checks the rto_mask to determine this and if so
it will request to pull one of those tasks to itself if the non running RT
task is of higher priority than the new priority of the next task to run on
the current CPU.
When we deal with large number of CPUs, the original pull logic suffered
from large lock contention on a single CPU run queue, which caused a huge
latency across all CPUs. This was caused by only having one CPU having
overloaded RT tasks and a bunch of other CPUs lowering their priority. To
solve this issue, commit:
b6366f048e0c ("sched/rt: Use IPI to trigger RT task push migration instead of pulling")
changed the way to request a pull. Instead of grabbing the lock of the
overloaded CPU's runqueue, it simply sent an IPI to that CPU to do the work.
Although the IPI logic worked very well in removing the large latency build
up, it still could suffer from a large number of IPIs being sent to a single
CPU. On a 80 CPU box, I measured over 200us of processing IPIs. Worse yet,
when I tested this on a 120 CPU box, with a stress test that had lots of
RT tasks scheduling on all CPUs, it actually triggered the hard lockup
detector! One CPU had so many IPIs sent to it, and due to the restart
mechanism that is triggered when the source run queue has a priority status
change, the CPU spent minutes! processing the IPIs.
Thinking about this further, I realized there's no reason for each run queue
to send its own IPI. As all CPUs with overloaded tasks must be scanned
regardless if there's one or many CPUs lowering their priority, because
there's no current way to find the CPU with the highest priority task that
can schedule to one of these CPUs, there really only needs to be one IPI
being sent around at a time.
This greatly simplifies the code!
The new approach is to have each root domain have its own irq work, as the
rto_mask is per root domain. The root domain has the following fields
attached to it:
rto_push_work - the irq work to process each CPU set in rto_mask
rto_lock - the lock to protect some of the other rto fields
rto_loop_start - an atomic that keeps contention down on rto_lock
the first CPU scheduling in a lower priority task
is the one to kick off the process.
rto_loop_next - an atomic that gets incremented for each CPU that
schedules in a lower priority task.
rto_loop - a variable protected by rto_lock that is used to
compare against rto_loop_next
rto_cpu - The cpu to send the next IPI to, also protected by
the rto_lock.
When a CPU schedules in a lower priority task and wants to make sure
overloaded CPUs know about it. It increments the rto_loop_next. Then it
atomically sets rto_loop_start with a cmpxchg. If the old value is not "0",
then it is done, as another CPU is kicking off the IPI loop. If the old
value is "0", then it will take the rto_lock to synchronize with a possible
IPI being sent around to the overloaded CPUs.
If rto_cpu is greater than or equal to nr_cpu_ids, then there's either no
IPI being sent around, or one is about to finish. Then rto_cpu is set to the
first CPU in rto_mask and an IPI is sent to that CPU. If there's no CPUs set
in rto_mask, then there's nothing to be done.
When the CPU receives the IPI, it will first try to push any RT tasks that is
queued on the CPU but can't run because a higher priority RT task is
currently running on that CPU.
Then it takes the rto_lock and looks for the next CPU in the rto_mask. If it
finds one, it simply sends an IPI to that CPU and the process continues.
If there's no more CPUs in the rto_mask, then rto_loop is compared with
rto_loop_next. If they match, everything is done and the process is over. If
they do not match, then a CPU scheduled in a lower priority task as the IPI
was being passed around, and the process needs to start again. The first CPU
in rto_mask is sent the IPI.
This change removes this duplication of work in the IPI logic, and greatly
lowers the latency caused by the IPIs. This removed the lockup happening on
the 120 CPU machine. It also simplifies the code tremendously. What else
could anyone ask for?
Thanks to Peter Zijlstra for simplifying the rto_loop_start atomic logic and
supplying me with the rto_start_trylock() and rto_start_unlock() helper
functions.
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Clark Williams <williams@redhat.com>
Cc: Daniel Bristot de Oliveira <bristot@redhat.com>
Cc: John Kacur <jkacur@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Scott Wood <swood@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20170424114732.1aac6dc4@gandalf.local.home
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-10-06 18:05:04 +00:00
|
|
|
rd->rto_cpu = -1;
|
|
|
|
|
|
|
|
/*
|
|
|
|
* ACQUIRE ensures we see the @rto_mask changes
|
|
|
|
* made prior to the @next value observed.
|
|
|
|
*
|
|
|
|
* Matches WMB in rt_set_overload().
|
|
|
|
*/
|
|
|
|
next = atomic_read_acquire(&rd->rto_loop_next);
|
sched/rt: Use IPI to trigger RT task push migration instead of pulling
When debugging the latencies on a 40 core box, where we hit 300 to
500 microsecond latencies, I found there was a huge contention on the
runqueue locks.
Investigating it further, running ftrace, I found that it was due to
the pulling of RT tasks.
The test that was run was the following:
cyclictest --numa -p95 -m -d0 -i100
This created a thread on each CPU, that would set its wakeup in iterations
of 100 microseconds. The -d0 means that all the threads had the same
interval (100us). Each thread sleeps for 100us and wakes up and measures
its latencies.
cyclictest is maintained at:
git://git.kernel.org/pub/scm/linux/kernel/git/clrkwllms/rt-tests.git
What happened was another RT task would be scheduled on one of the CPUs
that was running our test, when the other CPU tests went to sleep and
scheduled idle. This caused the "pull" operation to execute on all
these CPUs. Each one of these saw the RT task that was overloaded on
the CPU of the test that was still running, and each one tried
to grab that task in a thundering herd way.
To grab the task, each thread would do a double rq lock grab, grabbing
its own lock as well as the rq of the overloaded CPU. As the sched
domains on this box was rather flat for its size, I saw up to 12 CPUs
block on this lock at once. This caused a ripple affect with the
rq locks especially since the taking was done via a double rq lock, which
means that several of the CPUs had their own rq locks held while trying
to take this rq lock. As these locks were blocked, any wakeups or load
balanceing on these CPUs would also block on these locks, and the wait
time escalated.
I've tried various methods to lessen the load, but things like an
atomic counter to only let one CPU grab the task wont work, because
the task may have a limited affinity, and we may pick the wrong
CPU to take that lock and do the pull, to only find out that the
CPU we picked isn't in the task's affinity.
Instead of doing the PULL, I now have the CPUs that want the pull to
send over an IPI to the overloaded CPU, and let that CPU pick what
CPU to push the task to. No more need to grab the rq lock, and the
push/pull algorithm still works fine.
With this patch, the latency dropped to just 150us over a 20 hour run.
Without the patch, the huge latencies would trigger in seconds.
I've created a new sched feature called RT_PUSH_IPI, which is enabled
by default.
When RT_PUSH_IPI is not enabled, the old method of grabbing the rq locks
and having the pulling CPU do the work is implemented. When RT_PUSH_IPI
is enabled, the IPI is sent to the overloaded CPU to do a push.
To enabled or disable this at run time:
# mount -t debugfs nodev /sys/kernel/debug
# echo RT_PUSH_IPI > /sys/kernel/debug/sched_features
or
# echo NO_RT_PUSH_IPI > /sys/kernel/debug/sched_features
Update: This original patch would send an IPI to all CPUs in the RT overload
list. But that could theoretically cause the reverse issue. That is, there
could be lots of overloaded RT queues and one CPU lowers its priority. It would
then send an IPI to all the overloaded RT queues and they could then all try
to grab the rq lock of the CPU lowering its priority, and then we have the
same problem.
The latest design sends out only one IPI to the first overloaded CPU. It tries to
push any tasks that it can, and then looks for the next overloaded CPU that can
push to the source CPU. The IPIs stop when all overloaded CPUs that have pushable
tasks that have priorities greater than the source CPU are covered. In case the
source CPU lowers its priority again, a flag is set to tell the IPI traversal to
restart with the first RT overloaded CPU after the source CPU.
Parts-suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Joern Engel <joern@purestorage.com>
Cc: Clark Williams <williams@redhat.com>
Cc: Mike Galbraith <umgwanakikbuti@gmail.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20150318144946.2f3cc982@gandalf.local.home
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2015-03-18 18:49:46 +00:00
|
|
|
|
sched/rt: Simplify the IPI based RT balancing logic
When a CPU lowers its priority (schedules out a high priority task for a
lower priority one), a check is made to see if any other CPU has overloaded
RT tasks (more than one). It checks the rto_mask to determine this and if so
it will request to pull one of those tasks to itself if the non running RT
task is of higher priority than the new priority of the next task to run on
the current CPU.
When we deal with large number of CPUs, the original pull logic suffered
from large lock contention on a single CPU run queue, which caused a huge
latency across all CPUs. This was caused by only having one CPU having
overloaded RT tasks and a bunch of other CPUs lowering their priority. To
solve this issue, commit:
b6366f048e0c ("sched/rt: Use IPI to trigger RT task push migration instead of pulling")
changed the way to request a pull. Instead of grabbing the lock of the
overloaded CPU's runqueue, it simply sent an IPI to that CPU to do the work.
Although the IPI logic worked very well in removing the large latency build
up, it still could suffer from a large number of IPIs being sent to a single
CPU. On a 80 CPU box, I measured over 200us of processing IPIs. Worse yet,
when I tested this on a 120 CPU box, with a stress test that had lots of
RT tasks scheduling on all CPUs, it actually triggered the hard lockup
detector! One CPU had so many IPIs sent to it, and due to the restart
mechanism that is triggered when the source run queue has a priority status
change, the CPU spent minutes! processing the IPIs.
Thinking about this further, I realized there's no reason for each run queue
to send its own IPI. As all CPUs with overloaded tasks must be scanned
regardless if there's one or many CPUs lowering their priority, because
there's no current way to find the CPU with the highest priority task that
can schedule to one of these CPUs, there really only needs to be one IPI
being sent around at a time.
This greatly simplifies the code!
The new approach is to have each root domain have its own irq work, as the
rto_mask is per root domain. The root domain has the following fields
attached to it:
rto_push_work - the irq work to process each CPU set in rto_mask
rto_lock - the lock to protect some of the other rto fields
rto_loop_start - an atomic that keeps contention down on rto_lock
the first CPU scheduling in a lower priority task
is the one to kick off the process.
rto_loop_next - an atomic that gets incremented for each CPU that
schedules in a lower priority task.
rto_loop - a variable protected by rto_lock that is used to
compare against rto_loop_next
rto_cpu - The cpu to send the next IPI to, also protected by
the rto_lock.
When a CPU schedules in a lower priority task and wants to make sure
overloaded CPUs know about it. It increments the rto_loop_next. Then it
atomically sets rto_loop_start with a cmpxchg. If the old value is not "0",
then it is done, as another CPU is kicking off the IPI loop. If the old
value is "0", then it will take the rto_lock to synchronize with a possible
IPI being sent around to the overloaded CPUs.
If rto_cpu is greater than or equal to nr_cpu_ids, then there's either no
IPI being sent around, or one is about to finish. Then rto_cpu is set to the
first CPU in rto_mask and an IPI is sent to that CPU. If there's no CPUs set
in rto_mask, then there's nothing to be done.
When the CPU receives the IPI, it will first try to push any RT tasks that is
queued on the CPU but can't run because a higher priority RT task is
currently running on that CPU.
Then it takes the rto_lock and looks for the next CPU in the rto_mask. If it
finds one, it simply sends an IPI to that CPU and the process continues.
If there's no more CPUs in the rto_mask, then rto_loop is compared with
rto_loop_next. If they match, everything is done and the process is over. If
they do not match, then a CPU scheduled in a lower priority task as the IPI
was being passed around, and the process needs to start again. The first CPU
in rto_mask is sent the IPI.
This change removes this duplication of work in the IPI logic, and greatly
lowers the latency caused by the IPIs. This removed the lockup happening on
the 120 CPU machine. It also simplifies the code tremendously. What else
could anyone ask for?
Thanks to Peter Zijlstra for simplifying the rto_loop_start atomic logic and
supplying me with the rto_start_trylock() and rto_start_unlock() helper
functions.
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Clark Williams <williams@redhat.com>
Cc: Daniel Bristot de Oliveira <bristot@redhat.com>
Cc: John Kacur <jkacur@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Scott Wood <swood@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20170424114732.1aac6dc4@gandalf.local.home
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-10-06 18:05:04 +00:00
|
|
|
if (rd->rto_loop == next)
|
sched/rt: Use IPI to trigger RT task push migration instead of pulling
When debugging the latencies on a 40 core box, where we hit 300 to
500 microsecond latencies, I found there was a huge contention on the
runqueue locks.
Investigating it further, running ftrace, I found that it was due to
the pulling of RT tasks.
The test that was run was the following:
cyclictest --numa -p95 -m -d0 -i100
This created a thread on each CPU, that would set its wakeup in iterations
of 100 microseconds. The -d0 means that all the threads had the same
interval (100us). Each thread sleeps for 100us and wakes up and measures
its latencies.
cyclictest is maintained at:
git://git.kernel.org/pub/scm/linux/kernel/git/clrkwllms/rt-tests.git
What happened was another RT task would be scheduled on one of the CPUs
that was running our test, when the other CPU tests went to sleep and
scheduled idle. This caused the "pull" operation to execute on all
these CPUs. Each one of these saw the RT task that was overloaded on
the CPU of the test that was still running, and each one tried
to grab that task in a thundering herd way.
To grab the task, each thread would do a double rq lock grab, grabbing
its own lock as well as the rq of the overloaded CPU. As the sched
domains on this box was rather flat for its size, I saw up to 12 CPUs
block on this lock at once. This caused a ripple affect with the
rq locks especially since the taking was done via a double rq lock, which
means that several of the CPUs had their own rq locks held while trying
to take this rq lock. As these locks were blocked, any wakeups or load
balanceing on these CPUs would also block on these locks, and the wait
time escalated.
I've tried various methods to lessen the load, but things like an
atomic counter to only let one CPU grab the task wont work, because
the task may have a limited affinity, and we may pick the wrong
CPU to take that lock and do the pull, to only find out that the
CPU we picked isn't in the task's affinity.
Instead of doing the PULL, I now have the CPUs that want the pull to
send over an IPI to the overloaded CPU, and let that CPU pick what
CPU to push the task to. No more need to grab the rq lock, and the
push/pull algorithm still works fine.
With this patch, the latency dropped to just 150us over a 20 hour run.
Without the patch, the huge latencies would trigger in seconds.
I've created a new sched feature called RT_PUSH_IPI, which is enabled
by default.
When RT_PUSH_IPI is not enabled, the old method of grabbing the rq locks
and having the pulling CPU do the work is implemented. When RT_PUSH_IPI
is enabled, the IPI is sent to the overloaded CPU to do a push.
To enabled or disable this at run time:
# mount -t debugfs nodev /sys/kernel/debug
# echo RT_PUSH_IPI > /sys/kernel/debug/sched_features
or
# echo NO_RT_PUSH_IPI > /sys/kernel/debug/sched_features
Update: This original patch would send an IPI to all CPUs in the RT overload
list. But that could theoretically cause the reverse issue. That is, there
could be lots of overloaded RT queues and one CPU lowers its priority. It would
then send an IPI to all the overloaded RT queues and they could then all try
to grab the rq lock of the CPU lowering its priority, and then we have the
same problem.
The latest design sends out only one IPI to the first overloaded CPU. It tries to
push any tasks that it can, and then looks for the next overloaded CPU that can
push to the source CPU. The IPIs stop when all overloaded CPUs that have pushable
tasks that have priorities greater than the source CPU are covered. In case the
source CPU lowers its priority again, a flag is set to tell the IPI traversal to
restart with the first RT overloaded CPU after the source CPU.
Parts-suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Joern Engel <joern@purestorage.com>
Cc: Clark Williams <williams@redhat.com>
Cc: Mike Galbraith <umgwanakikbuti@gmail.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20150318144946.2f3cc982@gandalf.local.home
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2015-03-18 18:49:46 +00:00
|
|
|
break;
|
sched/rt: Simplify the IPI based RT balancing logic
When a CPU lowers its priority (schedules out a high priority task for a
lower priority one), a check is made to see if any other CPU has overloaded
RT tasks (more than one). It checks the rto_mask to determine this and if so
it will request to pull one of those tasks to itself if the non running RT
task is of higher priority than the new priority of the next task to run on
the current CPU.
When we deal with large number of CPUs, the original pull logic suffered
from large lock contention on a single CPU run queue, which caused a huge
latency across all CPUs. This was caused by only having one CPU having
overloaded RT tasks and a bunch of other CPUs lowering their priority. To
solve this issue, commit:
b6366f048e0c ("sched/rt: Use IPI to trigger RT task push migration instead of pulling")
changed the way to request a pull. Instead of grabbing the lock of the
overloaded CPU's runqueue, it simply sent an IPI to that CPU to do the work.
Although the IPI logic worked very well in removing the large latency build
up, it still could suffer from a large number of IPIs being sent to a single
CPU. On a 80 CPU box, I measured over 200us of processing IPIs. Worse yet,
when I tested this on a 120 CPU box, with a stress test that had lots of
RT tasks scheduling on all CPUs, it actually triggered the hard lockup
detector! One CPU had so many IPIs sent to it, and due to the restart
mechanism that is triggered when the source run queue has a priority status
change, the CPU spent minutes! processing the IPIs.
Thinking about this further, I realized there's no reason for each run queue
to send its own IPI. As all CPUs with overloaded tasks must be scanned
regardless if there's one or many CPUs lowering their priority, because
there's no current way to find the CPU with the highest priority task that
can schedule to one of these CPUs, there really only needs to be one IPI
being sent around at a time.
This greatly simplifies the code!
The new approach is to have each root domain have its own irq work, as the
rto_mask is per root domain. The root domain has the following fields
attached to it:
rto_push_work - the irq work to process each CPU set in rto_mask
rto_lock - the lock to protect some of the other rto fields
rto_loop_start - an atomic that keeps contention down on rto_lock
the first CPU scheduling in a lower priority task
is the one to kick off the process.
rto_loop_next - an atomic that gets incremented for each CPU that
schedules in a lower priority task.
rto_loop - a variable protected by rto_lock that is used to
compare against rto_loop_next
rto_cpu - The cpu to send the next IPI to, also protected by
the rto_lock.
When a CPU schedules in a lower priority task and wants to make sure
overloaded CPUs know about it. It increments the rto_loop_next. Then it
atomically sets rto_loop_start with a cmpxchg. If the old value is not "0",
then it is done, as another CPU is kicking off the IPI loop. If the old
value is "0", then it will take the rto_lock to synchronize with a possible
IPI being sent around to the overloaded CPUs.
If rto_cpu is greater than or equal to nr_cpu_ids, then there's either no
IPI being sent around, or one is about to finish. Then rto_cpu is set to the
first CPU in rto_mask and an IPI is sent to that CPU. If there's no CPUs set
in rto_mask, then there's nothing to be done.
When the CPU receives the IPI, it will first try to push any RT tasks that is
queued on the CPU but can't run because a higher priority RT task is
currently running on that CPU.
Then it takes the rto_lock and looks for the next CPU in the rto_mask. If it
finds one, it simply sends an IPI to that CPU and the process continues.
If there's no more CPUs in the rto_mask, then rto_loop is compared with
rto_loop_next. If they match, everything is done and the process is over. If
they do not match, then a CPU scheduled in a lower priority task as the IPI
was being passed around, and the process needs to start again. The first CPU
in rto_mask is sent the IPI.
This change removes this duplication of work in the IPI logic, and greatly
lowers the latency caused by the IPIs. This removed the lockup happening on
the 120 CPU machine. It also simplifies the code tremendously. What else
could anyone ask for?
Thanks to Peter Zijlstra for simplifying the rto_loop_start atomic logic and
supplying me with the rto_start_trylock() and rto_start_unlock() helper
functions.
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Clark Williams <williams@redhat.com>
Cc: Daniel Bristot de Oliveira <bristot@redhat.com>
Cc: John Kacur <jkacur@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Scott Wood <swood@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20170424114732.1aac6dc4@gandalf.local.home
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-10-06 18:05:04 +00:00
|
|
|
|
|
|
|
rd->rto_loop = next;
|
sched/rt: Use IPI to trigger RT task push migration instead of pulling
When debugging the latencies on a 40 core box, where we hit 300 to
500 microsecond latencies, I found there was a huge contention on the
runqueue locks.
Investigating it further, running ftrace, I found that it was due to
the pulling of RT tasks.
The test that was run was the following:
cyclictest --numa -p95 -m -d0 -i100
This created a thread on each CPU, that would set its wakeup in iterations
of 100 microseconds. The -d0 means that all the threads had the same
interval (100us). Each thread sleeps for 100us and wakes up and measures
its latencies.
cyclictest is maintained at:
git://git.kernel.org/pub/scm/linux/kernel/git/clrkwllms/rt-tests.git
What happened was another RT task would be scheduled on one of the CPUs
that was running our test, when the other CPU tests went to sleep and
scheduled idle. This caused the "pull" operation to execute on all
these CPUs. Each one of these saw the RT task that was overloaded on
the CPU of the test that was still running, and each one tried
to grab that task in a thundering herd way.
To grab the task, each thread would do a double rq lock grab, grabbing
its own lock as well as the rq of the overloaded CPU. As the sched
domains on this box was rather flat for its size, I saw up to 12 CPUs
block on this lock at once. This caused a ripple affect with the
rq locks especially since the taking was done via a double rq lock, which
means that several of the CPUs had their own rq locks held while trying
to take this rq lock. As these locks were blocked, any wakeups or load
balanceing on these CPUs would also block on these locks, and the wait
time escalated.
I've tried various methods to lessen the load, but things like an
atomic counter to only let one CPU grab the task wont work, because
the task may have a limited affinity, and we may pick the wrong
CPU to take that lock and do the pull, to only find out that the
CPU we picked isn't in the task's affinity.
Instead of doing the PULL, I now have the CPUs that want the pull to
send over an IPI to the overloaded CPU, and let that CPU pick what
CPU to push the task to. No more need to grab the rq lock, and the
push/pull algorithm still works fine.
With this patch, the latency dropped to just 150us over a 20 hour run.
Without the patch, the huge latencies would trigger in seconds.
I've created a new sched feature called RT_PUSH_IPI, which is enabled
by default.
When RT_PUSH_IPI is not enabled, the old method of grabbing the rq locks
and having the pulling CPU do the work is implemented. When RT_PUSH_IPI
is enabled, the IPI is sent to the overloaded CPU to do a push.
To enabled or disable this at run time:
# mount -t debugfs nodev /sys/kernel/debug
# echo RT_PUSH_IPI > /sys/kernel/debug/sched_features
or
# echo NO_RT_PUSH_IPI > /sys/kernel/debug/sched_features
Update: This original patch would send an IPI to all CPUs in the RT overload
list. But that could theoretically cause the reverse issue. That is, there
could be lots of overloaded RT queues and one CPU lowers its priority. It would
then send an IPI to all the overloaded RT queues and they could then all try
to grab the rq lock of the CPU lowering its priority, and then we have the
same problem.
The latest design sends out only one IPI to the first overloaded CPU. It tries to
push any tasks that it can, and then looks for the next overloaded CPU that can
push to the source CPU. The IPIs stop when all overloaded CPUs that have pushable
tasks that have priorities greater than the source CPU are covered. In case the
source CPU lowers its priority again, a flag is set to tell the IPI traversal to
restart with the first RT overloaded CPU after the source CPU.
Parts-suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Joern Engel <joern@purestorage.com>
Cc: Clark Williams <williams@redhat.com>
Cc: Mike Galbraith <umgwanakikbuti@gmail.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20150318144946.2f3cc982@gandalf.local.home
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2015-03-18 18:49:46 +00:00
|
|
|
}
|
|
|
|
|
sched/rt: Simplify the IPI based RT balancing logic
When a CPU lowers its priority (schedules out a high priority task for a
lower priority one), a check is made to see if any other CPU has overloaded
RT tasks (more than one). It checks the rto_mask to determine this and if so
it will request to pull one of those tasks to itself if the non running RT
task is of higher priority than the new priority of the next task to run on
the current CPU.
When we deal with large number of CPUs, the original pull logic suffered
from large lock contention on a single CPU run queue, which caused a huge
latency across all CPUs. This was caused by only having one CPU having
overloaded RT tasks and a bunch of other CPUs lowering their priority. To
solve this issue, commit:
b6366f048e0c ("sched/rt: Use IPI to trigger RT task push migration instead of pulling")
changed the way to request a pull. Instead of grabbing the lock of the
overloaded CPU's runqueue, it simply sent an IPI to that CPU to do the work.
Although the IPI logic worked very well in removing the large latency build
up, it still could suffer from a large number of IPIs being sent to a single
CPU. On a 80 CPU box, I measured over 200us of processing IPIs. Worse yet,
when I tested this on a 120 CPU box, with a stress test that had lots of
RT tasks scheduling on all CPUs, it actually triggered the hard lockup
detector! One CPU had so many IPIs sent to it, and due to the restart
mechanism that is triggered when the source run queue has a priority status
change, the CPU spent minutes! processing the IPIs.
Thinking about this further, I realized there's no reason for each run queue
to send its own IPI. As all CPUs with overloaded tasks must be scanned
regardless if there's one or many CPUs lowering their priority, because
there's no current way to find the CPU with the highest priority task that
can schedule to one of these CPUs, there really only needs to be one IPI
being sent around at a time.
This greatly simplifies the code!
The new approach is to have each root domain have its own irq work, as the
rto_mask is per root domain. The root domain has the following fields
attached to it:
rto_push_work - the irq work to process each CPU set in rto_mask
rto_lock - the lock to protect some of the other rto fields
rto_loop_start - an atomic that keeps contention down on rto_lock
the first CPU scheduling in a lower priority task
is the one to kick off the process.
rto_loop_next - an atomic that gets incremented for each CPU that
schedules in a lower priority task.
rto_loop - a variable protected by rto_lock that is used to
compare against rto_loop_next
rto_cpu - The cpu to send the next IPI to, also protected by
the rto_lock.
When a CPU schedules in a lower priority task and wants to make sure
overloaded CPUs know about it. It increments the rto_loop_next. Then it
atomically sets rto_loop_start with a cmpxchg. If the old value is not "0",
then it is done, as another CPU is kicking off the IPI loop. If the old
value is "0", then it will take the rto_lock to synchronize with a possible
IPI being sent around to the overloaded CPUs.
If rto_cpu is greater than or equal to nr_cpu_ids, then there's either no
IPI being sent around, or one is about to finish. Then rto_cpu is set to the
first CPU in rto_mask and an IPI is sent to that CPU. If there's no CPUs set
in rto_mask, then there's nothing to be done.
When the CPU receives the IPI, it will first try to push any RT tasks that is
queued on the CPU but can't run because a higher priority RT task is
currently running on that CPU.
Then it takes the rto_lock and looks for the next CPU in the rto_mask. If it
finds one, it simply sends an IPI to that CPU and the process continues.
If there's no more CPUs in the rto_mask, then rto_loop is compared with
rto_loop_next. If they match, everything is done and the process is over. If
they do not match, then a CPU scheduled in a lower priority task as the IPI
was being passed around, and the process needs to start again. The first CPU
in rto_mask is sent the IPI.
This change removes this duplication of work in the IPI logic, and greatly
lowers the latency caused by the IPIs. This removed the lockup happening on
the 120 CPU machine. It also simplifies the code tremendously. What else
could anyone ask for?
Thanks to Peter Zijlstra for simplifying the rto_loop_start atomic logic and
supplying me with the rto_start_trylock() and rto_start_unlock() helper
functions.
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Clark Williams <williams@redhat.com>
Cc: Daniel Bristot de Oliveira <bristot@redhat.com>
Cc: John Kacur <jkacur@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Scott Wood <swood@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20170424114732.1aac6dc4@gandalf.local.home
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-10-06 18:05:04 +00:00
|
|
|
return -1;
|
sched/rt: Use IPI to trigger RT task push migration instead of pulling
When debugging the latencies on a 40 core box, where we hit 300 to
500 microsecond latencies, I found there was a huge contention on the
runqueue locks.
Investigating it further, running ftrace, I found that it was due to
the pulling of RT tasks.
The test that was run was the following:
cyclictest --numa -p95 -m -d0 -i100
This created a thread on each CPU, that would set its wakeup in iterations
of 100 microseconds. The -d0 means that all the threads had the same
interval (100us). Each thread sleeps for 100us and wakes up and measures
its latencies.
cyclictest is maintained at:
git://git.kernel.org/pub/scm/linux/kernel/git/clrkwllms/rt-tests.git
What happened was another RT task would be scheduled on one of the CPUs
that was running our test, when the other CPU tests went to sleep and
scheduled idle. This caused the "pull" operation to execute on all
these CPUs. Each one of these saw the RT task that was overloaded on
the CPU of the test that was still running, and each one tried
to grab that task in a thundering herd way.
To grab the task, each thread would do a double rq lock grab, grabbing
its own lock as well as the rq of the overloaded CPU. As the sched
domains on this box was rather flat for its size, I saw up to 12 CPUs
block on this lock at once. This caused a ripple affect with the
rq locks especially since the taking was done via a double rq lock, which
means that several of the CPUs had their own rq locks held while trying
to take this rq lock. As these locks were blocked, any wakeups or load
balanceing on these CPUs would also block on these locks, and the wait
time escalated.
I've tried various methods to lessen the load, but things like an
atomic counter to only let one CPU grab the task wont work, because
the task may have a limited affinity, and we may pick the wrong
CPU to take that lock and do the pull, to only find out that the
CPU we picked isn't in the task's affinity.
Instead of doing the PULL, I now have the CPUs that want the pull to
send over an IPI to the overloaded CPU, and let that CPU pick what
CPU to push the task to. No more need to grab the rq lock, and the
push/pull algorithm still works fine.
With this patch, the latency dropped to just 150us over a 20 hour run.
Without the patch, the huge latencies would trigger in seconds.
I've created a new sched feature called RT_PUSH_IPI, which is enabled
by default.
When RT_PUSH_IPI is not enabled, the old method of grabbing the rq locks
and having the pulling CPU do the work is implemented. When RT_PUSH_IPI
is enabled, the IPI is sent to the overloaded CPU to do a push.
To enabled or disable this at run time:
# mount -t debugfs nodev /sys/kernel/debug
# echo RT_PUSH_IPI > /sys/kernel/debug/sched_features
or
# echo NO_RT_PUSH_IPI > /sys/kernel/debug/sched_features
Update: This original patch would send an IPI to all CPUs in the RT overload
list. But that could theoretically cause the reverse issue. That is, there
could be lots of overloaded RT queues and one CPU lowers its priority. It would
then send an IPI to all the overloaded RT queues and they could then all try
to grab the rq lock of the CPU lowering its priority, and then we have the
same problem.
The latest design sends out only one IPI to the first overloaded CPU. It tries to
push any tasks that it can, and then looks for the next overloaded CPU that can
push to the source CPU. The IPIs stop when all overloaded CPUs that have pushable
tasks that have priorities greater than the source CPU are covered. In case the
source CPU lowers its priority again, a flag is set to tell the IPI traversal to
restart with the first RT overloaded CPU after the source CPU.
Parts-suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Joern Engel <joern@purestorage.com>
Cc: Clark Williams <williams@redhat.com>
Cc: Mike Galbraith <umgwanakikbuti@gmail.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20150318144946.2f3cc982@gandalf.local.home
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2015-03-18 18:49:46 +00:00
|
|
|
}
|
|
|
|
|
sched/rt: Simplify the IPI based RT balancing logic
When a CPU lowers its priority (schedules out a high priority task for a
lower priority one), a check is made to see if any other CPU has overloaded
RT tasks (more than one). It checks the rto_mask to determine this and if so
it will request to pull one of those tasks to itself if the non running RT
task is of higher priority than the new priority of the next task to run on
the current CPU.
When we deal with large number of CPUs, the original pull logic suffered
from large lock contention on a single CPU run queue, which caused a huge
latency across all CPUs. This was caused by only having one CPU having
overloaded RT tasks and a bunch of other CPUs lowering their priority. To
solve this issue, commit:
b6366f048e0c ("sched/rt: Use IPI to trigger RT task push migration instead of pulling")
changed the way to request a pull. Instead of grabbing the lock of the
overloaded CPU's runqueue, it simply sent an IPI to that CPU to do the work.
Although the IPI logic worked very well in removing the large latency build
up, it still could suffer from a large number of IPIs being sent to a single
CPU. On a 80 CPU box, I measured over 200us of processing IPIs. Worse yet,
when I tested this on a 120 CPU box, with a stress test that had lots of
RT tasks scheduling on all CPUs, it actually triggered the hard lockup
detector! One CPU had so many IPIs sent to it, and due to the restart
mechanism that is triggered when the source run queue has a priority status
change, the CPU spent minutes! processing the IPIs.
Thinking about this further, I realized there's no reason for each run queue
to send its own IPI. As all CPUs with overloaded tasks must be scanned
regardless if there's one or many CPUs lowering their priority, because
there's no current way to find the CPU with the highest priority task that
can schedule to one of these CPUs, there really only needs to be one IPI
being sent around at a time.
This greatly simplifies the code!
The new approach is to have each root domain have its own irq work, as the
rto_mask is per root domain. The root domain has the following fields
attached to it:
rto_push_work - the irq work to process each CPU set in rto_mask
rto_lock - the lock to protect some of the other rto fields
rto_loop_start - an atomic that keeps contention down on rto_lock
the first CPU scheduling in a lower priority task
is the one to kick off the process.
rto_loop_next - an atomic that gets incremented for each CPU that
schedules in a lower priority task.
rto_loop - a variable protected by rto_lock that is used to
compare against rto_loop_next
rto_cpu - The cpu to send the next IPI to, also protected by
the rto_lock.
When a CPU schedules in a lower priority task and wants to make sure
overloaded CPUs know about it. It increments the rto_loop_next. Then it
atomically sets rto_loop_start with a cmpxchg. If the old value is not "0",
then it is done, as another CPU is kicking off the IPI loop. If the old
value is "0", then it will take the rto_lock to synchronize with a possible
IPI being sent around to the overloaded CPUs.
If rto_cpu is greater than or equal to nr_cpu_ids, then there's either no
IPI being sent around, or one is about to finish. Then rto_cpu is set to the
first CPU in rto_mask and an IPI is sent to that CPU. If there's no CPUs set
in rto_mask, then there's nothing to be done.
When the CPU receives the IPI, it will first try to push any RT tasks that is
queued on the CPU but can't run because a higher priority RT task is
currently running on that CPU.
Then it takes the rto_lock and looks for the next CPU in the rto_mask. If it
finds one, it simply sends an IPI to that CPU and the process continues.
If there's no more CPUs in the rto_mask, then rto_loop is compared with
rto_loop_next. If they match, everything is done and the process is over. If
they do not match, then a CPU scheduled in a lower priority task as the IPI
was being passed around, and the process needs to start again. The first CPU
in rto_mask is sent the IPI.
This change removes this duplication of work in the IPI logic, and greatly
lowers the latency caused by the IPIs. This removed the lockup happening on
the 120 CPU machine. It also simplifies the code tremendously. What else
could anyone ask for?
Thanks to Peter Zijlstra for simplifying the rto_loop_start atomic logic and
supplying me with the rto_start_trylock() and rto_start_unlock() helper
functions.
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Clark Williams <williams@redhat.com>
Cc: Daniel Bristot de Oliveira <bristot@redhat.com>
Cc: John Kacur <jkacur@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Scott Wood <swood@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20170424114732.1aac6dc4@gandalf.local.home
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-10-06 18:05:04 +00:00
|
|
|
static inline bool rto_start_trylock(atomic_t *v)
|
|
|
|
{
|
|
|
|
return !atomic_cmpxchg_acquire(v, 0, 1);
|
|
|
|
}
|
sched/rt: Use IPI to trigger RT task push migration instead of pulling
When debugging the latencies on a 40 core box, where we hit 300 to
500 microsecond latencies, I found there was a huge contention on the
runqueue locks.
Investigating it further, running ftrace, I found that it was due to
the pulling of RT tasks.
The test that was run was the following:
cyclictest --numa -p95 -m -d0 -i100
This created a thread on each CPU, that would set its wakeup in iterations
of 100 microseconds. The -d0 means that all the threads had the same
interval (100us). Each thread sleeps for 100us and wakes up and measures
its latencies.
cyclictest is maintained at:
git://git.kernel.org/pub/scm/linux/kernel/git/clrkwllms/rt-tests.git
What happened was another RT task would be scheduled on one of the CPUs
that was running our test, when the other CPU tests went to sleep and
scheduled idle. This caused the "pull" operation to execute on all
these CPUs. Each one of these saw the RT task that was overloaded on
the CPU of the test that was still running, and each one tried
to grab that task in a thundering herd way.
To grab the task, each thread would do a double rq lock grab, grabbing
its own lock as well as the rq of the overloaded CPU. As the sched
domains on this box was rather flat for its size, I saw up to 12 CPUs
block on this lock at once. This caused a ripple affect with the
rq locks especially since the taking was done via a double rq lock, which
means that several of the CPUs had their own rq locks held while trying
to take this rq lock. As these locks were blocked, any wakeups or load
balanceing on these CPUs would also block on these locks, and the wait
time escalated.
I've tried various methods to lessen the load, but things like an
atomic counter to only let one CPU grab the task wont work, because
the task may have a limited affinity, and we may pick the wrong
CPU to take that lock and do the pull, to only find out that the
CPU we picked isn't in the task's affinity.
Instead of doing the PULL, I now have the CPUs that want the pull to
send over an IPI to the overloaded CPU, and let that CPU pick what
CPU to push the task to. No more need to grab the rq lock, and the
push/pull algorithm still works fine.
With this patch, the latency dropped to just 150us over a 20 hour run.
Without the patch, the huge latencies would trigger in seconds.
I've created a new sched feature called RT_PUSH_IPI, which is enabled
by default.
When RT_PUSH_IPI is not enabled, the old method of grabbing the rq locks
and having the pulling CPU do the work is implemented. When RT_PUSH_IPI
is enabled, the IPI is sent to the overloaded CPU to do a push.
To enabled or disable this at run time:
# mount -t debugfs nodev /sys/kernel/debug
# echo RT_PUSH_IPI > /sys/kernel/debug/sched_features
or
# echo NO_RT_PUSH_IPI > /sys/kernel/debug/sched_features
Update: This original patch would send an IPI to all CPUs in the RT overload
list. But that could theoretically cause the reverse issue. That is, there
could be lots of overloaded RT queues and one CPU lowers its priority. It would
then send an IPI to all the overloaded RT queues and they could then all try
to grab the rq lock of the CPU lowering its priority, and then we have the
same problem.
The latest design sends out only one IPI to the first overloaded CPU. It tries to
push any tasks that it can, and then looks for the next overloaded CPU that can
push to the source CPU. The IPIs stop when all overloaded CPUs that have pushable
tasks that have priorities greater than the source CPU are covered. In case the
source CPU lowers its priority again, a flag is set to tell the IPI traversal to
restart with the first RT overloaded CPU after the source CPU.
Parts-suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Joern Engel <joern@purestorage.com>
Cc: Clark Williams <williams@redhat.com>
Cc: Mike Galbraith <umgwanakikbuti@gmail.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20150318144946.2f3cc982@gandalf.local.home
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2015-03-18 18:49:46 +00:00
|
|
|
|
sched/rt: Simplify the IPI based RT balancing logic
When a CPU lowers its priority (schedules out a high priority task for a
lower priority one), a check is made to see if any other CPU has overloaded
RT tasks (more than one). It checks the rto_mask to determine this and if so
it will request to pull one of those tasks to itself if the non running RT
task is of higher priority than the new priority of the next task to run on
the current CPU.
When we deal with large number of CPUs, the original pull logic suffered
from large lock contention on a single CPU run queue, which caused a huge
latency across all CPUs. This was caused by only having one CPU having
overloaded RT tasks and a bunch of other CPUs lowering their priority. To
solve this issue, commit:
b6366f048e0c ("sched/rt: Use IPI to trigger RT task push migration instead of pulling")
changed the way to request a pull. Instead of grabbing the lock of the
overloaded CPU's runqueue, it simply sent an IPI to that CPU to do the work.
Although the IPI logic worked very well in removing the large latency build
up, it still could suffer from a large number of IPIs being sent to a single
CPU. On a 80 CPU box, I measured over 200us of processing IPIs. Worse yet,
when I tested this on a 120 CPU box, with a stress test that had lots of
RT tasks scheduling on all CPUs, it actually triggered the hard lockup
detector! One CPU had so many IPIs sent to it, and due to the restart
mechanism that is triggered when the source run queue has a priority status
change, the CPU spent minutes! processing the IPIs.
Thinking about this further, I realized there's no reason for each run queue
to send its own IPI. As all CPUs with overloaded tasks must be scanned
regardless if there's one or many CPUs lowering their priority, because
there's no current way to find the CPU with the highest priority task that
can schedule to one of these CPUs, there really only needs to be one IPI
being sent around at a time.
This greatly simplifies the code!
The new approach is to have each root domain have its own irq work, as the
rto_mask is per root domain. The root domain has the following fields
attached to it:
rto_push_work - the irq work to process each CPU set in rto_mask
rto_lock - the lock to protect some of the other rto fields
rto_loop_start - an atomic that keeps contention down on rto_lock
the first CPU scheduling in a lower priority task
is the one to kick off the process.
rto_loop_next - an atomic that gets incremented for each CPU that
schedules in a lower priority task.
rto_loop - a variable protected by rto_lock that is used to
compare against rto_loop_next
rto_cpu - The cpu to send the next IPI to, also protected by
the rto_lock.
When a CPU schedules in a lower priority task and wants to make sure
overloaded CPUs know about it. It increments the rto_loop_next. Then it
atomically sets rto_loop_start with a cmpxchg. If the old value is not "0",
then it is done, as another CPU is kicking off the IPI loop. If the old
value is "0", then it will take the rto_lock to synchronize with a possible
IPI being sent around to the overloaded CPUs.
If rto_cpu is greater than or equal to nr_cpu_ids, then there's either no
IPI being sent around, or one is about to finish. Then rto_cpu is set to the
first CPU in rto_mask and an IPI is sent to that CPU. If there's no CPUs set
in rto_mask, then there's nothing to be done.
When the CPU receives the IPI, it will first try to push any RT tasks that is
queued on the CPU but can't run because a higher priority RT task is
currently running on that CPU.
Then it takes the rto_lock and looks for the next CPU in the rto_mask. If it
finds one, it simply sends an IPI to that CPU and the process continues.
If there's no more CPUs in the rto_mask, then rto_loop is compared with
rto_loop_next. If they match, everything is done and the process is over. If
they do not match, then a CPU scheduled in a lower priority task as the IPI
was being passed around, and the process needs to start again. The first CPU
in rto_mask is sent the IPI.
This change removes this duplication of work in the IPI logic, and greatly
lowers the latency caused by the IPIs. This removed the lockup happening on
the 120 CPU machine. It also simplifies the code tremendously. What else
could anyone ask for?
Thanks to Peter Zijlstra for simplifying the rto_loop_start atomic logic and
supplying me with the rto_start_trylock() and rto_start_unlock() helper
functions.
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Clark Williams <williams@redhat.com>
Cc: Daniel Bristot de Oliveira <bristot@redhat.com>
Cc: John Kacur <jkacur@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Scott Wood <swood@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20170424114732.1aac6dc4@gandalf.local.home
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-10-06 18:05:04 +00:00
|
|
|
static inline void rto_start_unlock(atomic_t *v)
|
sched/rt: Use IPI to trigger RT task push migration instead of pulling
When debugging the latencies on a 40 core box, where we hit 300 to
500 microsecond latencies, I found there was a huge contention on the
runqueue locks.
Investigating it further, running ftrace, I found that it was due to
the pulling of RT tasks.
The test that was run was the following:
cyclictest --numa -p95 -m -d0 -i100
This created a thread on each CPU, that would set its wakeup in iterations
of 100 microseconds. The -d0 means that all the threads had the same
interval (100us). Each thread sleeps for 100us and wakes up and measures
its latencies.
cyclictest is maintained at:
git://git.kernel.org/pub/scm/linux/kernel/git/clrkwllms/rt-tests.git
What happened was another RT task would be scheduled on one of the CPUs
that was running our test, when the other CPU tests went to sleep and
scheduled idle. This caused the "pull" operation to execute on all
these CPUs. Each one of these saw the RT task that was overloaded on
the CPU of the test that was still running, and each one tried
to grab that task in a thundering herd way.
To grab the task, each thread would do a double rq lock grab, grabbing
its own lock as well as the rq of the overloaded CPU. As the sched
domains on this box was rather flat for its size, I saw up to 12 CPUs
block on this lock at once. This caused a ripple affect with the
rq locks especially since the taking was done via a double rq lock, which
means that several of the CPUs had their own rq locks held while trying
to take this rq lock. As these locks were blocked, any wakeups or load
balanceing on these CPUs would also block on these locks, and the wait
time escalated.
I've tried various methods to lessen the load, but things like an
atomic counter to only let one CPU grab the task wont work, because
the task may have a limited affinity, and we may pick the wrong
CPU to take that lock and do the pull, to only find out that the
CPU we picked isn't in the task's affinity.
Instead of doing the PULL, I now have the CPUs that want the pull to
send over an IPI to the overloaded CPU, and let that CPU pick what
CPU to push the task to. No more need to grab the rq lock, and the
push/pull algorithm still works fine.
With this patch, the latency dropped to just 150us over a 20 hour run.
Without the patch, the huge latencies would trigger in seconds.
I've created a new sched feature called RT_PUSH_IPI, which is enabled
by default.
When RT_PUSH_IPI is not enabled, the old method of grabbing the rq locks
and having the pulling CPU do the work is implemented. When RT_PUSH_IPI
is enabled, the IPI is sent to the overloaded CPU to do a push.
To enabled or disable this at run time:
# mount -t debugfs nodev /sys/kernel/debug
# echo RT_PUSH_IPI > /sys/kernel/debug/sched_features
or
# echo NO_RT_PUSH_IPI > /sys/kernel/debug/sched_features
Update: This original patch would send an IPI to all CPUs in the RT overload
list. But that could theoretically cause the reverse issue. That is, there
could be lots of overloaded RT queues and one CPU lowers its priority. It would
then send an IPI to all the overloaded RT queues and they could then all try
to grab the rq lock of the CPU lowering its priority, and then we have the
same problem.
The latest design sends out only one IPI to the first overloaded CPU. It tries to
push any tasks that it can, and then looks for the next overloaded CPU that can
push to the source CPU. The IPIs stop when all overloaded CPUs that have pushable
tasks that have priorities greater than the source CPU are covered. In case the
source CPU lowers its priority again, a flag is set to tell the IPI traversal to
restart with the first RT overloaded CPU after the source CPU.
Parts-suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Joern Engel <joern@purestorage.com>
Cc: Clark Williams <williams@redhat.com>
Cc: Mike Galbraith <umgwanakikbuti@gmail.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20150318144946.2f3cc982@gandalf.local.home
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2015-03-18 18:49:46 +00:00
|
|
|
{
|
sched/rt: Simplify the IPI based RT balancing logic
When a CPU lowers its priority (schedules out a high priority task for a
lower priority one), a check is made to see if any other CPU has overloaded
RT tasks (more than one). It checks the rto_mask to determine this and if so
it will request to pull one of those tasks to itself if the non running RT
task is of higher priority than the new priority of the next task to run on
the current CPU.
When we deal with large number of CPUs, the original pull logic suffered
from large lock contention on a single CPU run queue, which caused a huge
latency across all CPUs. This was caused by only having one CPU having
overloaded RT tasks and a bunch of other CPUs lowering their priority. To
solve this issue, commit:
b6366f048e0c ("sched/rt: Use IPI to trigger RT task push migration instead of pulling")
changed the way to request a pull. Instead of grabbing the lock of the
overloaded CPU's runqueue, it simply sent an IPI to that CPU to do the work.
Although the IPI logic worked very well in removing the large latency build
up, it still could suffer from a large number of IPIs being sent to a single
CPU. On a 80 CPU box, I measured over 200us of processing IPIs. Worse yet,
when I tested this on a 120 CPU box, with a stress test that had lots of
RT tasks scheduling on all CPUs, it actually triggered the hard lockup
detector! One CPU had so many IPIs sent to it, and due to the restart
mechanism that is triggered when the source run queue has a priority status
change, the CPU spent minutes! processing the IPIs.
Thinking about this further, I realized there's no reason for each run queue
to send its own IPI. As all CPUs with overloaded tasks must be scanned
regardless if there's one or many CPUs lowering their priority, because
there's no current way to find the CPU with the highest priority task that
can schedule to one of these CPUs, there really only needs to be one IPI
being sent around at a time.
This greatly simplifies the code!
The new approach is to have each root domain have its own irq work, as the
rto_mask is per root domain. The root domain has the following fields
attached to it:
rto_push_work - the irq work to process each CPU set in rto_mask
rto_lock - the lock to protect some of the other rto fields
rto_loop_start - an atomic that keeps contention down on rto_lock
the first CPU scheduling in a lower priority task
is the one to kick off the process.
rto_loop_next - an atomic that gets incremented for each CPU that
schedules in a lower priority task.
rto_loop - a variable protected by rto_lock that is used to
compare against rto_loop_next
rto_cpu - The cpu to send the next IPI to, also protected by
the rto_lock.
When a CPU schedules in a lower priority task and wants to make sure
overloaded CPUs know about it. It increments the rto_loop_next. Then it
atomically sets rto_loop_start with a cmpxchg. If the old value is not "0",
then it is done, as another CPU is kicking off the IPI loop. If the old
value is "0", then it will take the rto_lock to synchronize with a possible
IPI being sent around to the overloaded CPUs.
If rto_cpu is greater than or equal to nr_cpu_ids, then there's either no
IPI being sent around, or one is about to finish. Then rto_cpu is set to the
first CPU in rto_mask and an IPI is sent to that CPU. If there's no CPUs set
in rto_mask, then there's nothing to be done.
When the CPU receives the IPI, it will first try to push any RT tasks that is
queued on the CPU but can't run because a higher priority RT task is
currently running on that CPU.
Then it takes the rto_lock and looks for the next CPU in the rto_mask. If it
finds one, it simply sends an IPI to that CPU and the process continues.
If there's no more CPUs in the rto_mask, then rto_loop is compared with
rto_loop_next. If they match, everything is done and the process is over. If
they do not match, then a CPU scheduled in a lower priority task as the IPI
was being passed around, and the process needs to start again. The first CPU
in rto_mask is sent the IPI.
This change removes this duplication of work in the IPI logic, and greatly
lowers the latency caused by the IPIs. This removed the lockup happening on
the 120 CPU machine. It also simplifies the code tremendously. What else
could anyone ask for?
Thanks to Peter Zijlstra for simplifying the rto_loop_start atomic logic and
supplying me with the rto_start_trylock() and rto_start_unlock() helper
functions.
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Clark Williams <williams@redhat.com>
Cc: Daniel Bristot de Oliveira <bristot@redhat.com>
Cc: John Kacur <jkacur@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Scott Wood <swood@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20170424114732.1aac6dc4@gandalf.local.home
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-10-06 18:05:04 +00:00
|
|
|
atomic_set_release(v, 0);
|
|
|
|
}
|
sched/rt: Use IPI to trigger RT task push migration instead of pulling
When debugging the latencies on a 40 core box, where we hit 300 to
500 microsecond latencies, I found there was a huge contention on the
runqueue locks.
Investigating it further, running ftrace, I found that it was due to
the pulling of RT tasks.
The test that was run was the following:
cyclictest --numa -p95 -m -d0 -i100
This created a thread on each CPU, that would set its wakeup in iterations
of 100 microseconds. The -d0 means that all the threads had the same
interval (100us). Each thread sleeps for 100us and wakes up and measures
its latencies.
cyclictest is maintained at:
git://git.kernel.org/pub/scm/linux/kernel/git/clrkwllms/rt-tests.git
What happened was another RT task would be scheduled on one of the CPUs
that was running our test, when the other CPU tests went to sleep and
scheduled idle. This caused the "pull" operation to execute on all
these CPUs. Each one of these saw the RT task that was overloaded on
the CPU of the test that was still running, and each one tried
to grab that task in a thundering herd way.
To grab the task, each thread would do a double rq lock grab, grabbing
its own lock as well as the rq of the overloaded CPU. As the sched
domains on this box was rather flat for its size, I saw up to 12 CPUs
block on this lock at once. This caused a ripple affect with the
rq locks especially since the taking was done via a double rq lock, which
means that several of the CPUs had their own rq locks held while trying
to take this rq lock. As these locks were blocked, any wakeups or load
balanceing on these CPUs would also block on these locks, and the wait
time escalated.
I've tried various methods to lessen the load, but things like an
atomic counter to only let one CPU grab the task wont work, because
the task may have a limited affinity, and we may pick the wrong
CPU to take that lock and do the pull, to only find out that the
CPU we picked isn't in the task's affinity.
Instead of doing the PULL, I now have the CPUs that want the pull to
send over an IPI to the overloaded CPU, and let that CPU pick what
CPU to push the task to. No more need to grab the rq lock, and the
push/pull algorithm still works fine.
With this patch, the latency dropped to just 150us over a 20 hour run.
Without the patch, the huge latencies would trigger in seconds.
I've created a new sched feature called RT_PUSH_IPI, which is enabled
by default.
When RT_PUSH_IPI is not enabled, the old method of grabbing the rq locks
and having the pulling CPU do the work is implemented. When RT_PUSH_IPI
is enabled, the IPI is sent to the overloaded CPU to do a push.
To enabled or disable this at run time:
# mount -t debugfs nodev /sys/kernel/debug
# echo RT_PUSH_IPI > /sys/kernel/debug/sched_features
or
# echo NO_RT_PUSH_IPI > /sys/kernel/debug/sched_features
Update: This original patch would send an IPI to all CPUs in the RT overload
list. But that could theoretically cause the reverse issue. That is, there
could be lots of overloaded RT queues and one CPU lowers its priority. It would
then send an IPI to all the overloaded RT queues and they could then all try
to grab the rq lock of the CPU lowering its priority, and then we have the
same problem.
The latest design sends out only one IPI to the first overloaded CPU. It tries to
push any tasks that it can, and then looks for the next overloaded CPU that can
push to the source CPU. The IPIs stop when all overloaded CPUs that have pushable
tasks that have priorities greater than the source CPU are covered. In case the
source CPU lowers its priority again, a flag is set to tell the IPI traversal to
restart with the first RT overloaded CPU after the source CPU.
Parts-suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Joern Engel <joern@purestorage.com>
Cc: Clark Williams <williams@redhat.com>
Cc: Mike Galbraith <umgwanakikbuti@gmail.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20150318144946.2f3cc982@gandalf.local.home
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2015-03-18 18:49:46 +00:00
|
|
|
|
sched/rt: Simplify the IPI based RT balancing logic
When a CPU lowers its priority (schedules out a high priority task for a
lower priority one), a check is made to see if any other CPU has overloaded
RT tasks (more than one). It checks the rto_mask to determine this and if so
it will request to pull one of those tasks to itself if the non running RT
task is of higher priority than the new priority of the next task to run on
the current CPU.
When we deal with large number of CPUs, the original pull logic suffered
from large lock contention on a single CPU run queue, which caused a huge
latency across all CPUs. This was caused by only having one CPU having
overloaded RT tasks and a bunch of other CPUs lowering their priority. To
solve this issue, commit:
b6366f048e0c ("sched/rt: Use IPI to trigger RT task push migration instead of pulling")
changed the way to request a pull. Instead of grabbing the lock of the
overloaded CPU's runqueue, it simply sent an IPI to that CPU to do the work.
Although the IPI logic worked very well in removing the large latency build
up, it still could suffer from a large number of IPIs being sent to a single
CPU. On a 80 CPU box, I measured over 200us of processing IPIs. Worse yet,
when I tested this on a 120 CPU box, with a stress test that had lots of
RT tasks scheduling on all CPUs, it actually triggered the hard lockup
detector! One CPU had so many IPIs sent to it, and due to the restart
mechanism that is triggered when the source run queue has a priority status
change, the CPU spent minutes! processing the IPIs.
Thinking about this further, I realized there's no reason for each run queue
to send its own IPI. As all CPUs with overloaded tasks must be scanned
regardless if there's one or many CPUs lowering their priority, because
there's no current way to find the CPU with the highest priority task that
can schedule to one of these CPUs, there really only needs to be one IPI
being sent around at a time.
This greatly simplifies the code!
The new approach is to have each root domain have its own irq work, as the
rto_mask is per root domain. The root domain has the following fields
attached to it:
rto_push_work - the irq work to process each CPU set in rto_mask
rto_lock - the lock to protect some of the other rto fields
rto_loop_start - an atomic that keeps contention down on rto_lock
the first CPU scheduling in a lower priority task
is the one to kick off the process.
rto_loop_next - an atomic that gets incremented for each CPU that
schedules in a lower priority task.
rto_loop - a variable protected by rto_lock that is used to
compare against rto_loop_next
rto_cpu - The cpu to send the next IPI to, also protected by
the rto_lock.
When a CPU schedules in a lower priority task and wants to make sure
overloaded CPUs know about it. It increments the rto_loop_next. Then it
atomically sets rto_loop_start with a cmpxchg. If the old value is not "0",
then it is done, as another CPU is kicking off the IPI loop. If the old
value is "0", then it will take the rto_lock to synchronize with a possible
IPI being sent around to the overloaded CPUs.
If rto_cpu is greater than or equal to nr_cpu_ids, then there's either no
IPI being sent around, or one is about to finish. Then rto_cpu is set to the
first CPU in rto_mask and an IPI is sent to that CPU. If there's no CPUs set
in rto_mask, then there's nothing to be done.
When the CPU receives the IPI, it will first try to push any RT tasks that is
queued on the CPU but can't run because a higher priority RT task is
currently running on that CPU.
Then it takes the rto_lock and looks for the next CPU in the rto_mask. If it
finds one, it simply sends an IPI to that CPU and the process continues.
If there's no more CPUs in the rto_mask, then rto_loop is compared with
rto_loop_next. If they match, everything is done and the process is over. If
they do not match, then a CPU scheduled in a lower priority task as the IPI
was being passed around, and the process needs to start again. The first CPU
in rto_mask is sent the IPI.
This change removes this duplication of work in the IPI logic, and greatly
lowers the latency caused by the IPIs. This removed the lockup happening on
the 120 CPU machine. It also simplifies the code tremendously. What else
could anyone ask for?
Thanks to Peter Zijlstra for simplifying the rto_loop_start atomic logic and
supplying me with the rto_start_trylock() and rto_start_unlock() helper
functions.
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Clark Williams <williams@redhat.com>
Cc: Daniel Bristot de Oliveira <bristot@redhat.com>
Cc: John Kacur <jkacur@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Scott Wood <swood@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20170424114732.1aac6dc4@gandalf.local.home
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-10-06 18:05:04 +00:00
|
|
|
static void tell_cpu_to_push(struct rq *rq)
|
|
|
|
{
|
|
|
|
int cpu = -1;
|
sched/rt: Use IPI to trigger RT task push migration instead of pulling
When debugging the latencies on a 40 core box, where we hit 300 to
500 microsecond latencies, I found there was a huge contention on the
runqueue locks.
Investigating it further, running ftrace, I found that it was due to
the pulling of RT tasks.
The test that was run was the following:
cyclictest --numa -p95 -m -d0 -i100
This created a thread on each CPU, that would set its wakeup in iterations
of 100 microseconds. The -d0 means that all the threads had the same
interval (100us). Each thread sleeps for 100us and wakes up and measures
its latencies.
cyclictest is maintained at:
git://git.kernel.org/pub/scm/linux/kernel/git/clrkwllms/rt-tests.git
What happened was another RT task would be scheduled on one of the CPUs
that was running our test, when the other CPU tests went to sleep and
scheduled idle. This caused the "pull" operation to execute on all
these CPUs. Each one of these saw the RT task that was overloaded on
the CPU of the test that was still running, and each one tried
to grab that task in a thundering herd way.
To grab the task, each thread would do a double rq lock grab, grabbing
its own lock as well as the rq of the overloaded CPU. As the sched
domains on this box was rather flat for its size, I saw up to 12 CPUs
block on this lock at once. This caused a ripple affect with the
rq locks especially since the taking was done via a double rq lock, which
means that several of the CPUs had their own rq locks held while trying
to take this rq lock. As these locks were blocked, any wakeups or load
balanceing on these CPUs would also block on these locks, and the wait
time escalated.
I've tried various methods to lessen the load, but things like an
atomic counter to only let one CPU grab the task wont work, because
the task may have a limited affinity, and we may pick the wrong
CPU to take that lock and do the pull, to only find out that the
CPU we picked isn't in the task's affinity.
Instead of doing the PULL, I now have the CPUs that want the pull to
send over an IPI to the overloaded CPU, and let that CPU pick what
CPU to push the task to. No more need to grab the rq lock, and the
push/pull algorithm still works fine.
With this patch, the latency dropped to just 150us over a 20 hour run.
Without the patch, the huge latencies would trigger in seconds.
I've created a new sched feature called RT_PUSH_IPI, which is enabled
by default.
When RT_PUSH_IPI is not enabled, the old method of grabbing the rq locks
and having the pulling CPU do the work is implemented. When RT_PUSH_IPI
is enabled, the IPI is sent to the overloaded CPU to do a push.
To enabled or disable this at run time:
# mount -t debugfs nodev /sys/kernel/debug
# echo RT_PUSH_IPI > /sys/kernel/debug/sched_features
or
# echo NO_RT_PUSH_IPI > /sys/kernel/debug/sched_features
Update: This original patch would send an IPI to all CPUs in the RT overload
list. But that could theoretically cause the reverse issue. That is, there
could be lots of overloaded RT queues and one CPU lowers its priority. It would
then send an IPI to all the overloaded RT queues and they could then all try
to grab the rq lock of the CPU lowering its priority, and then we have the
same problem.
The latest design sends out only one IPI to the first overloaded CPU. It tries to
push any tasks that it can, and then looks for the next overloaded CPU that can
push to the source CPU. The IPIs stop when all overloaded CPUs that have pushable
tasks that have priorities greater than the source CPU are covered. In case the
source CPU lowers its priority again, a flag is set to tell the IPI traversal to
restart with the first RT overloaded CPU after the source CPU.
Parts-suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Joern Engel <joern@purestorage.com>
Cc: Clark Williams <williams@redhat.com>
Cc: Mike Galbraith <umgwanakikbuti@gmail.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20150318144946.2f3cc982@gandalf.local.home
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2015-03-18 18:49:46 +00:00
|
|
|
|
sched/rt: Simplify the IPI based RT balancing logic
When a CPU lowers its priority (schedules out a high priority task for a
lower priority one), a check is made to see if any other CPU has overloaded
RT tasks (more than one). It checks the rto_mask to determine this and if so
it will request to pull one of those tasks to itself if the non running RT
task is of higher priority than the new priority of the next task to run on
the current CPU.
When we deal with large number of CPUs, the original pull logic suffered
from large lock contention on a single CPU run queue, which caused a huge
latency across all CPUs. This was caused by only having one CPU having
overloaded RT tasks and a bunch of other CPUs lowering their priority. To
solve this issue, commit:
b6366f048e0c ("sched/rt: Use IPI to trigger RT task push migration instead of pulling")
changed the way to request a pull. Instead of grabbing the lock of the
overloaded CPU's runqueue, it simply sent an IPI to that CPU to do the work.
Although the IPI logic worked very well in removing the large latency build
up, it still could suffer from a large number of IPIs being sent to a single
CPU. On a 80 CPU box, I measured over 200us of processing IPIs. Worse yet,
when I tested this on a 120 CPU box, with a stress test that had lots of
RT tasks scheduling on all CPUs, it actually triggered the hard lockup
detector! One CPU had so many IPIs sent to it, and due to the restart
mechanism that is triggered when the source run queue has a priority status
change, the CPU spent minutes! processing the IPIs.
Thinking about this further, I realized there's no reason for each run queue
to send its own IPI. As all CPUs with overloaded tasks must be scanned
regardless if there's one or many CPUs lowering their priority, because
there's no current way to find the CPU with the highest priority task that
can schedule to one of these CPUs, there really only needs to be one IPI
being sent around at a time.
This greatly simplifies the code!
The new approach is to have each root domain have its own irq work, as the
rto_mask is per root domain. The root domain has the following fields
attached to it:
rto_push_work - the irq work to process each CPU set in rto_mask
rto_lock - the lock to protect some of the other rto fields
rto_loop_start - an atomic that keeps contention down on rto_lock
the first CPU scheduling in a lower priority task
is the one to kick off the process.
rto_loop_next - an atomic that gets incremented for each CPU that
schedules in a lower priority task.
rto_loop - a variable protected by rto_lock that is used to
compare against rto_loop_next
rto_cpu - The cpu to send the next IPI to, also protected by
the rto_lock.
When a CPU schedules in a lower priority task and wants to make sure
overloaded CPUs know about it. It increments the rto_loop_next. Then it
atomically sets rto_loop_start with a cmpxchg. If the old value is not "0",
then it is done, as another CPU is kicking off the IPI loop. If the old
value is "0", then it will take the rto_lock to synchronize with a possible
IPI being sent around to the overloaded CPUs.
If rto_cpu is greater than or equal to nr_cpu_ids, then there's either no
IPI being sent around, or one is about to finish. Then rto_cpu is set to the
first CPU in rto_mask and an IPI is sent to that CPU. If there's no CPUs set
in rto_mask, then there's nothing to be done.
When the CPU receives the IPI, it will first try to push any RT tasks that is
queued on the CPU but can't run because a higher priority RT task is
currently running on that CPU.
Then it takes the rto_lock and looks for the next CPU in the rto_mask. If it
finds one, it simply sends an IPI to that CPU and the process continues.
If there's no more CPUs in the rto_mask, then rto_loop is compared with
rto_loop_next. If they match, everything is done and the process is over. If
they do not match, then a CPU scheduled in a lower priority task as the IPI
was being passed around, and the process needs to start again. The first CPU
in rto_mask is sent the IPI.
This change removes this duplication of work in the IPI logic, and greatly
lowers the latency caused by the IPIs. This removed the lockup happening on
the 120 CPU machine. It also simplifies the code tremendously. What else
could anyone ask for?
Thanks to Peter Zijlstra for simplifying the rto_loop_start atomic logic and
supplying me with the rto_start_trylock() and rto_start_unlock() helper
functions.
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Clark Williams <williams@redhat.com>
Cc: Daniel Bristot de Oliveira <bristot@redhat.com>
Cc: John Kacur <jkacur@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Scott Wood <swood@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20170424114732.1aac6dc4@gandalf.local.home
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-10-06 18:05:04 +00:00
|
|
|
/* Keep the loop going if the IPI is currently active */
|
|
|
|
atomic_inc(&rq->rd->rto_loop_next);
|
sched/rt: Use IPI to trigger RT task push migration instead of pulling
When debugging the latencies on a 40 core box, where we hit 300 to
500 microsecond latencies, I found there was a huge contention on the
runqueue locks.
Investigating it further, running ftrace, I found that it was due to
the pulling of RT tasks.
The test that was run was the following:
cyclictest --numa -p95 -m -d0 -i100
This created a thread on each CPU, that would set its wakeup in iterations
of 100 microseconds. The -d0 means that all the threads had the same
interval (100us). Each thread sleeps for 100us and wakes up and measures
its latencies.
cyclictest is maintained at:
git://git.kernel.org/pub/scm/linux/kernel/git/clrkwllms/rt-tests.git
What happened was another RT task would be scheduled on one of the CPUs
that was running our test, when the other CPU tests went to sleep and
scheduled idle. This caused the "pull" operation to execute on all
these CPUs. Each one of these saw the RT task that was overloaded on
the CPU of the test that was still running, and each one tried
to grab that task in a thundering herd way.
To grab the task, each thread would do a double rq lock grab, grabbing
its own lock as well as the rq of the overloaded CPU. As the sched
domains on this box was rather flat for its size, I saw up to 12 CPUs
block on this lock at once. This caused a ripple affect with the
rq locks especially since the taking was done via a double rq lock, which
means that several of the CPUs had their own rq locks held while trying
to take this rq lock. As these locks were blocked, any wakeups or load
balanceing on these CPUs would also block on these locks, and the wait
time escalated.
I've tried various methods to lessen the load, but things like an
atomic counter to only let one CPU grab the task wont work, because
the task may have a limited affinity, and we may pick the wrong
CPU to take that lock and do the pull, to only find out that the
CPU we picked isn't in the task's affinity.
Instead of doing the PULL, I now have the CPUs that want the pull to
send over an IPI to the overloaded CPU, and let that CPU pick what
CPU to push the task to. No more need to grab the rq lock, and the
push/pull algorithm still works fine.
With this patch, the latency dropped to just 150us over a 20 hour run.
Without the patch, the huge latencies would trigger in seconds.
I've created a new sched feature called RT_PUSH_IPI, which is enabled
by default.
When RT_PUSH_IPI is not enabled, the old method of grabbing the rq locks
and having the pulling CPU do the work is implemented. When RT_PUSH_IPI
is enabled, the IPI is sent to the overloaded CPU to do a push.
To enabled or disable this at run time:
# mount -t debugfs nodev /sys/kernel/debug
# echo RT_PUSH_IPI > /sys/kernel/debug/sched_features
or
# echo NO_RT_PUSH_IPI > /sys/kernel/debug/sched_features
Update: This original patch would send an IPI to all CPUs in the RT overload
list. But that could theoretically cause the reverse issue. That is, there
could be lots of overloaded RT queues and one CPU lowers its priority. It would
then send an IPI to all the overloaded RT queues and they could then all try
to grab the rq lock of the CPU lowering its priority, and then we have the
same problem.
The latest design sends out only one IPI to the first overloaded CPU. It tries to
push any tasks that it can, and then looks for the next overloaded CPU that can
push to the source CPU. The IPIs stop when all overloaded CPUs that have pushable
tasks that have priorities greater than the source CPU are covered. In case the
source CPU lowers its priority again, a flag is set to tell the IPI traversal to
restart with the first RT overloaded CPU after the source CPU.
Parts-suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Joern Engel <joern@purestorage.com>
Cc: Clark Williams <williams@redhat.com>
Cc: Mike Galbraith <umgwanakikbuti@gmail.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20150318144946.2f3cc982@gandalf.local.home
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2015-03-18 18:49:46 +00:00
|
|
|
|
sched/rt: Simplify the IPI based RT balancing logic
When a CPU lowers its priority (schedules out a high priority task for a
lower priority one), a check is made to see if any other CPU has overloaded
RT tasks (more than one). It checks the rto_mask to determine this and if so
it will request to pull one of those tasks to itself if the non running RT
task is of higher priority than the new priority of the next task to run on
the current CPU.
When we deal with large number of CPUs, the original pull logic suffered
from large lock contention on a single CPU run queue, which caused a huge
latency across all CPUs. This was caused by only having one CPU having
overloaded RT tasks and a bunch of other CPUs lowering their priority. To
solve this issue, commit:
b6366f048e0c ("sched/rt: Use IPI to trigger RT task push migration instead of pulling")
changed the way to request a pull. Instead of grabbing the lock of the
overloaded CPU's runqueue, it simply sent an IPI to that CPU to do the work.
Although the IPI logic worked very well in removing the large latency build
up, it still could suffer from a large number of IPIs being sent to a single
CPU. On a 80 CPU box, I measured over 200us of processing IPIs. Worse yet,
when I tested this on a 120 CPU box, with a stress test that had lots of
RT tasks scheduling on all CPUs, it actually triggered the hard lockup
detector! One CPU had so many IPIs sent to it, and due to the restart
mechanism that is triggered when the source run queue has a priority status
change, the CPU spent minutes! processing the IPIs.
Thinking about this further, I realized there's no reason for each run queue
to send its own IPI. As all CPUs with overloaded tasks must be scanned
regardless if there's one or many CPUs lowering their priority, because
there's no current way to find the CPU with the highest priority task that
can schedule to one of these CPUs, there really only needs to be one IPI
being sent around at a time.
This greatly simplifies the code!
The new approach is to have each root domain have its own irq work, as the
rto_mask is per root domain. The root domain has the following fields
attached to it:
rto_push_work - the irq work to process each CPU set in rto_mask
rto_lock - the lock to protect some of the other rto fields
rto_loop_start - an atomic that keeps contention down on rto_lock
the first CPU scheduling in a lower priority task
is the one to kick off the process.
rto_loop_next - an atomic that gets incremented for each CPU that
schedules in a lower priority task.
rto_loop - a variable protected by rto_lock that is used to
compare against rto_loop_next
rto_cpu - The cpu to send the next IPI to, also protected by
the rto_lock.
When a CPU schedules in a lower priority task and wants to make sure
overloaded CPUs know about it. It increments the rto_loop_next. Then it
atomically sets rto_loop_start with a cmpxchg. If the old value is not "0",
then it is done, as another CPU is kicking off the IPI loop. If the old
value is "0", then it will take the rto_lock to synchronize with a possible
IPI being sent around to the overloaded CPUs.
If rto_cpu is greater than or equal to nr_cpu_ids, then there's either no
IPI being sent around, or one is about to finish. Then rto_cpu is set to the
first CPU in rto_mask and an IPI is sent to that CPU. If there's no CPUs set
in rto_mask, then there's nothing to be done.
When the CPU receives the IPI, it will first try to push any RT tasks that is
queued on the CPU but can't run because a higher priority RT task is
currently running on that CPU.
Then it takes the rto_lock and looks for the next CPU in the rto_mask. If it
finds one, it simply sends an IPI to that CPU and the process continues.
If there's no more CPUs in the rto_mask, then rto_loop is compared with
rto_loop_next. If they match, everything is done and the process is over. If
they do not match, then a CPU scheduled in a lower priority task as the IPI
was being passed around, and the process needs to start again. The first CPU
in rto_mask is sent the IPI.
This change removes this duplication of work in the IPI logic, and greatly
lowers the latency caused by the IPIs. This removed the lockup happening on
the 120 CPU machine. It also simplifies the code tremendously. What else
could anyone ask for?
Thanks to Peter Zijlstra for simplifying the rto_loop_start atomic logic and
supplying me with the rto_start_trylock() and rto_start_unlock() helper
functions.
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Clark Williams <williams@redhat.com>
Cc: Daniel Bristot de Oliveira <bristot@redhat.com>
Cc: John Kacur <jkacur@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Scott Wood <swood@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20170424114732.1aac6dc4@gandalf.local.home
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-10-06 18:05:04 +00:00
|
|
|
/* Only one CPU can initiate a loop at a time */
|
|
|
|
if (!rto_start_trylock(&rq->rd->rto_loop_start))
|
sched/rt: Use IPI to trigger RT task push migration instead of pulling
When debugging the latencies on a 40 core box, where we hit 300 to
500 microsecond latencies, I found there was a huge contention on the
runqueue locks.
Investigating it further, running ftrace, I found that it was due to
the pulling of RT tasks.
The test that was run was the following:
cyclictest --numa -p95 -m -d0 -i100
This created a thread on each CPU, that would set its wakeup in iterations
of 100 microseconds. The -d0 means that all the threads had the same
interval (100us). Each thread sleeps for 100us and wakes up and measures
its latencies.
cyclictest is maintained at:
git://git.kernel.org/pub/scm/linux/kernel/git/clrkwllms/rt-tests.git
What happened was another RT task would be scheduled on one of the CPUs
that was running our test, when the other CPU tests went to sleep and
scheduled idle. This caused the "pull" operation to execute on all
these CPUs. Each one of these saw the RT task that was overloaded on
the CPU of the test that was still running, and each one tried
to grab that task in a thundering herd way.
To grab the task, each thread would do a double rq lock grab, grabbing
its own lock as well as the rq of the overloaded CPU. As the sched
domains on this box was rather flat for its size, I saw up to 12 CPUs
block on this lock at once. This caused a ripple affect with the
rq locks especially since the taking was done via a double rq lock, which
means that several of the CPUs had their own rq locks held while trying
to take this rq lock. As these locks were blocked, any wakeups or load
balanceing on these CPUs would also block on these locks, and the wait
time escalated.
I've tried various methods to lessen the load, but things like an
atomic counter to only let one CPU grab the task wont work, because
the task may have a limited affinity, and we may pick the wrong
CPU to take that lock and do the pull, to only find out that the
CPU we picked isn't in the task's affinity.
Instead of doing the PULL, I now have the CPUs that want the pull to
send over an IPI to the overloaded CPU, and let that CPU pick what
CPU to push the task to. No more need to grab the rq lock, and the
push/pull algorithm still works fine.
With this patch, the latency dropped to just 150us over a 20 hour run.
Without the patch, the huge latencies would trigger in seconds.
I've created a new sched feature called RT_PUSH_IPI, which is enabled
by default.
When RT_PUSH_IPI is not enabled, the old method of grabbing the rq locks
and having the pulling CPU do the work is implemented. When RT_PUSH_IPI
is enabled, the IPI is sent to the overloaded CPU to do a push.
To enabled or disable this at run time:
# mount -t debugfs nodev /sys/kernel/debug
# echo RT_PUSH_IPI > /sys/kernel/debug/sched_features
or
# echo NO_RT_PUSH_IPI > /sys/kernel/debug/sched_features
Update: This original patch would send an IPI to all CPUs in the RT overload
list. But that could theoretically cause the reverse issue. That is, there
could be lots of overloaded RT queues and one CPU lowers its priority. It would
then send an IPI to all the overloaded RT queues and they could then all try
to grab the rq lock of the CPU lowering its priority, and then we have the
same problem.
The latest design sends out only one IPI to the first overloaded CPU. It tries to
push any tasks that it can, and then looks for the next overloaded CPU that can
push to the source CPU. The IPIs stop when all overloaded CPUs that have pushable
tasks that have priorities greater than the source CPU are covered. In case the
source CPU lowers its priority again, a flag is set to tell the IPI traversal to
restart with the first RT overloaded CPU after the source CPU.
Parts-suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Joern Engel <joern@purestorage.com>
Cc: Clark Williams <williams@redhat.com>
Cc: Mike Galbraith <umgwanakikbuti@gmail.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20150318144946.2f3cc982@gandalf.local.home
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2015-03-18 18:49:46 +00:00
|
|
|
return;
|
|
|
|
|
sched/rt: Simplify the IPI based RT balancing logic
When a CPU lowers its priority (schedules out a high priority task for a
lower priority one), a check is made to see if any other CPU has overloaded
RT tasks (more than one). It checks the rto_mask to determine this and if so
it will request to pull one of those tasks to itself if the non running RT
task is of higher priority than the new priority of the next task to run on
the current CPU.
When we deal with large number of CPUs, the original pull logic suffered
from large lock contention on a single CPU run queue, which caused a huge
latency across all CPUs. This was caused by only having one CPU having
overloaded RT tasks and a bunch of other CPUs lowering their priority. To
solve this issue, commit:
b6366f048e0c ("sched/rt: Use IPI to trigger RT task push migration instead of pulling")
changed the way to request a pull. Instead of grabbing the lock of the
overloaded CPU's runqueue, it simply sent an IPI to that CPU to do the work.
Although the IPI logic worked very well in removing the large latency build
up, it still could suffer from a large number of IPIs being sent to a single
CPU. On a 80 CPU box, I measured over 200us of processing IPIs. Worse yet,
when I tested this on a 120 CPU box, with a stress test that had lots of
RT tasks scheduling on all CPUs, it actually triggered the hard lockup
detector! One CPU had so many IPIs sent to it, and due to the restart
mechanism that is triggered when the source run queue has a priority status
change, the CPU spent minutes! processing the IPIs.
Thinking about this further, I realized there's no reason for each run queue
to send its own IPI. As all CPUs with overloaded tasks must be scanned
regardless if there's one or many CPUs lowering their priority, because
there's no current way to find the CPU with the highest priority task that
can schedule to one of these CPUs, there really only needs to be one IPI
being sent around at a time.
This greatly simplifies the code!
The new approach is to have each root domain have its own irq work, as the
rto_mask is per root domain. The root domain has the following fields
attached to it:
rto_push_work - the irq work to process each CPU set in rto_mask
rto_lock - the lock to protect some of the other rto fields
rto_loop_start - an atomic that keeps contention down on rto_lock
the first CPU scheduling in a lower priority task
is the one to kick off the process.
rto_loop_next - an atomic that gets incremented for each CPU that
schedules in a lower priority task.
rto_loop - a variable protected by rto_lock that is used to
compare against rto_loop_next
rto_cpu - The cpu to send the next IPI to, also protected by
the rto_lock.
When a CPU schedules in a lower priority task and wants to make sure
overloaded CPUs know about it. It increments the rto_loop_next. Then it
atomically sets rto_loop_start with a cmpxchg. If the old value is not "0",
then it is done, as another CPU is kicking off the IPI loop. If the old
value is "0", then it will take the rto_lock to synchronize with a possible
IPI being sent around to the overloaded CPUs.
If rto_cpu is greater than or equal to nr_cpu_ids, then there's either no
IPI being sent around, or one is about to finish. Then rto_cpu is set to the
first CPU in rto_mask and an IPI is sent to that CPU. If there's no CPUs set
in rto_mask, then there's nothing to be done.
When the CPU receives the IPI, it will first try to push any RT tasks that is
queued on the CPU but can't run because a higher priority RT task is
currently running on that CPU.
Then it takes the rto_lock and looks for the next CPU in the rto_mask. If it
finds one, it simply sends an IPI to that CPU and the process continues.
If there's no more CPUs in the rto_mask, then rto_loop is compared with
rto_loop_next. If they match, everything is done and the process is over. If
they do not match, then a CPU scheduled in a lower priority task as the IPI
was being passed around, and the process needs to start again. The first CPU
in rto_mask is sent the IPI.
This change removes this duplication of work in the IPI logic, and greatly
lowers the latency caused by the IPIs. This removed the lockup happening on
the 120 CPU machine. It also simplifies the code tremendously. What else
could anyone ask for?
Thanks to Peter Zijlstra for simplifying the rto_loop_start atomic logic and
supplying me with the rto_start_trylock() and rto_start_unlock() helper
functions.
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Clark Williams <williams@redhat.com>
Cc: Daniel Bristot de Oliveira <bristot@redhat.com>
Cc: John Kacur <jkacur@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Scott Wood <swood@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20170424114732.1aac6dc4@gandalf.local.home
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-10-06 18:05:04 +00:00
|
|
|
raw_spin_lock(&rq->rd->rto_lock);
|
sched/rt: Use IPI to trigger RT task push migration instead of pulling
When debugging the latencies on a 40 core box, where we hit 300 to
500 microsecond latencies, I found there was a huge contention on the
runqueue locks.
Investigating it further, running ftrace, I found that it was due to
the pulling of RT tasks.
The test that was run was the following:
cyclictest --numa -p95 -m -d0 -i100
This created a thread on each CPU, that would set its wakeup in iterations
of 100 microseconds. The -d0 means that all the threads had the same
interval (100us). Each thread sleeps for 100us and wakes up and measures
its latencies.
cyclictest is maintained at:
git://git.kernel.org/pub/scm/linux/kernel/git/clrkwllms/rt-tests.git
What happened was another RT task would be scheduled on one of the CPUs
that was running our test, when the other CPU tests went to sleep and
scheduled idle. This caused the "pull" operation to execute on all
these CPUs. Each one of these saw the RT task that was overloaded on
the CPU of the test that was still running, and each one tried
to grab that task in a thundering herd way.
To grab the task, each thread would do a double rq lock grab, grabbing
its own lock as well as the rq of the overloaded CPU. As the sched
domains on this box was rather flat for its size, I saw up to 12 CPUs
block on this lock at once. This caused a ripple affect with the
rq locks especially since the taking was done via a double rq lock, which
means that several of the CPUs had their own rq locks held while trying
to take this rq lock. As these locks were blocked, any wakeups or load
balanceing on these CPUs would also block on these locks, and the wait
time escalated.
I've tried various methods to lessen the load, but things like an
atomic counter to only let one CPU grab the task wont work, because
the task may have a limited affinity, and we may pick the wrong
CPU to take that lock and do the pull, to only find out that the
CPU we picked isn't in the task's affinity.
Instead of doing the PULL, I now have the CPUs that want the pull to
send over an IPI to the overloaded CPU, and let that CPU pick what
CPU to push the task to. No more need to grab the rq lock, and the
push/pull algorithm still works fine.
With this patch, the latency dropped to just 150us over a 20 hour run.
Without the patch, the huge latencies would trigger in seconds.
I've created a new sched feature called RT_PUSH_IPI, which is enabled
by default.
When RT_PUSH_IPI is not enabled, the old method of grabbing the rq locks
and having the pulling CPU do the work is implemented. When RT_PUSH_IPI
is enabled, the IPI is sent to the overloaded CPU to do a push.
To enabled or disable this at run time:
# mount -t debugfs nodev /sys/kernel/debug
# echo RT_PUSH_IPI > /sys/kernel/debug/sched_features
or
# echo NO_RT_PUSH_IPI > /sys/kernel/debug/sched_features
Update: This original patch would send an IPI to all CPUs in the RT overload
list. But that could theoretically cause the reverse issue. That is, there
could be lots of overloaded RT queues and one CPU lowers its priority. It would
then send an IPI to all the overloaded RT queues and they could then all try
to grab the rq lock of the CPU lowering its priority, and then we have the
same problem.
The latest design sends out only one IPI to the first overloaded CPU. It tries to
push any tasks that it can, and then looks for the next overloaded CPU that can
push to the source CPU. The IPIs stop when all overloaded CPUs that have pushable
tasks that have priorities greater than the source CPU are covered. In case the
source CPU lowers its priority again, a flag is set to tell the IPI traversal to
restart with the first RT overloaded CPU after the source CPU.
Parts-suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Joern Engel <joern@purestorage.com>
Cc: Clark Williams <williams@redhat.com>
Cc: Mike Galbraith <umgwanakikbuti@gmail.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20150318144946.2f3cc982@gandalf.local.home
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2015-03-18 18:49:46 +00:00
|
|
|
|
sched/rt: Simplify the IPI based RT balancing logic
When a CPU lowers its priority (schedules out a high priority task for a
lower priority one), a check is made to see if any other CPU has overloaded
RT tasks (more than one). It checks the rto_mask to determine this and if so
it will request to pull one of those tasks to itself if the non running RT
task is of higher priority than the new priority of the next task to run on
the current CPU.
When we deal with large number of CPUs, the original pull logic suffered
from large lock contention on a single CPU run queue, which caused a huge
latency across all CPUs. This was caused by only having one CPU having
overloaded RT tasks and a bunch of other CPUs lowering their priority. To
solve this issue, commit:
b6366f048e0c ("sched/rt: Use IPI to trigger RT task push migration instead of pulling")
changed the way to request a pull. Instead of grabbing the lock of the
overloaded CPU's runqueue, it simply sent an IPI to that CPU to do the work.
Although the IPI logic worked very well in removing the large latency build
up, it still could suffer from a large number of IPIs being sent to a single
CPU. On a 80 CPU box, I measured over 200us of processing IPIs. Worse yet,
when I tested this on a 120 CPU box, with a stress test that had lots of
RT tasks scheduling on all CPUs, it actually triggered the hard lockup
detector! One CPU had so many IPIs sent to it, and due to the restart
mechanism that is triggered when the source run queue has a priority status
change, the CPU spent minutes! processing the IPIs.
Thinking about this further, I realized there's no reason for each run queue
to send its own IPI. As all CPUs with overloaded tasks must be scanned
regardless if there's one or many CPUs lowering their priority, because
there's no current way to find the CPU with the highest priority task that
can schedule to one of these CPUs, there really only needs to be one IPI
being sent around at a time.
This greatly simplifies the code!
The new approach is to have each root domain have its own irq work, as the
rto_mask is per root domain. The root domain has the following fields
attached to it:
rto_push_work - the irq work to process each CPU set in rto_mask
rto_lock - the lock to protect some of the other rto fields
rto_loop_start - an atomic that keeps contention down on rto_lock
the first CPU scheduling in a lower priority task
is the one to kick off the process.
rto_loop_next - an atomic that gets incremented for each CPU that
schedules in a lower priority task.
rto_loop - a variable protected by rto_lock that is used to
compare against rto_loop_next
rto_cpu - The cpu to send the next IPI to, also protected by
the rto_lock.
When a CPU schedules in a lower priority task and wants to make sure
overloaded CPUs know about it. It increments the rto_loop_next. Then it
atomically sets rto_loop_start with a cmpxchg. If the old value is not "0",
then it is done, as another CPU is kicking off the IPI loop. If the old
value is "0", then it will take the rto_lock to synchronize with a possible
IPI being sent around to the overloaded CPUs.
If rto_cpu is greater than or equal to nr_cpu_ids, then there's either no
IPI being sent around, or one is about to finish. Then rto_cpu is set to the
first CPU in rto_mask and an IPI is sent to that CPU. If there's no CPUs set
in rto_mask, then there's nothing to be done.
When the CPU receives the IPI, it will first try to push any RT tasks that is
queued on the CPU but can't run because a higher priority RT task is
currently running on that CPU.
Then it takes the rto_lock and looks for the next CPU in the rto_mask. If it
finds one, it simply sends an IPI to that CPU and the process continues.
If there's no more CPUs in the rto_mask, then rto_loop is compared with
rto_loop_next. If they match, everything is done and the process is over. If
they do not match, then a CPU scheduled in a lower priority task as the IPI
was being passed around, and the process needs to start again. The first CPU
in rto_mask is sent the IPI.
This change removes this duplication of work in the IPI logic, and greatly
lowers the latency caused by the IPIs. This removed the lockup happening on
the 120 CPU machine. It also simplifies the code tremendously. What else
could anyone ask for?
Thanks to Peter Zijlstra for simplifying the rto_loop_start atomic logic and
supplying me with the rto_start_trylock() and rto_start_unlock() helper
functions.
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Clark Williams <williams@redhat.com>
Cc: Daniel Bristot de Oliveira <bristot@redhat.com>
Cc: John Kacur <jkacur@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Scott Wood <swood@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20170424114732.1aac6dc4@gandalf.local.home
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-10-06 18:05:04 +00:00
|
|
|
/*
|
sched: Clean up and harmonize the coding style of the scheduler code base
A good number of small style inconsistencies have accumulated
in the scheduler core, so do a pass over them to harmonize
all these details:
- fix speling in comments,
- use curly braces for multi-line statements,
- remove unnecessary parentheses from integer literals,
- capitalize consistently,
- remove stray newlines,
- add comments where necessary,
- remove invalid/unnecessary comments,
- align structure definitions and other data types vertically,
- add missing newlines for increased readability,
- fix vertical tabulation where it's misaligned,
- harmonize preprocessor conditional block labeling
and vertical alignment,
- remove line-breaks where they uglify the code,
- add newline after local variable definitions,
No change in functionality:
md5:
1191fa0a890cfa8132156d2959d7e9e2 built-in.o.before.asm
1191fa0a890cfa8132156d2959d7e9e2 built-in.o.after.asm
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-03-03 13:01:12 +00:00
|
|
|
* The rto_cpu is updated under the lock, if it has a valid CPU
|
sched/rt: Simplify the IPI based RT balancing logic
When a CPU lowers its priority (schedules out a high priority task for a
lower priority one), a check is made to see if any other CPU has overloaded
RT tasks (more than one). It checks the rto_mask to determine this and if so
it will request to pull one of those tasks to itself if the non running RT
task is of higher priority than the new priority of the next task to run on
the current CPU.
When we deal with large number of CPUs, the original pull logic suffered
from large lock contention on a single CPU run queue, which caused a huge
latency across all CPUs. This was caused by only having one CPU having
overloaded RT tasks and a bunch of other CPUs lowering their priority. To
solve this issue, commit:
b6366f048e0c ("sched/rt: Use IPI to trigger RT task push migration instead of pulling")
changed the way to request a pull. Instead of grabbing the lock of the
overloaded CPU's runqueue, it simply sent an IPI to that CPU to do the work.
Although the IPI logic worked very well in removing the large latency build
up, it still could suffer from a large number of IPIs being sent to a single
CPU. On a 80 CPU box, I measured over 200us of processing IPIs. Worse yet,
when I tested this on a 120 CPU box, with a stress test that had lots of
RT tasks scheduling on all CPUs, it actually triggered the hard lockup
detector! One CPU had so many IPIs sent to it, and due to the restart
mechanism that is triggered when the source run queue has a priority status
change, the CPU spent minutes! processing the IPIs.
Thinking about this further, I realized there's no reason for each run queue
to send its own IPI. As all CPUs with overloaded tasks must be scanned
regardless if there's one or many CPUs lowering their priority, because
there's no current way to find the CPU with the highest priority task that
can schedule to one of these CPUs, there really only needs to be one IPI
being sent around at a time.
This greatly simplifies the code!
The new approach is to have each root domain have its own irq work, as the
rto_mask is per root domain. The root domain has the following fields
attached to it:
rto_push_work - the irq work to process each CPU set in rto_mask
rto_lock - the lock to protect some of the other rto fields
rto_loop_start - an atomic that keeps contention down on rto_lock
the first CPU scheduling in a lower priority task
is the one to kick off the process.
rto_loop_next - an atomic that gets incremented for each CPU that
schedules in a lower priority task.
rto_loop - a variable protected by rto_lock that is used to
compare against rto_loop_next
rto_cpu - The cpu to send the next IPI to, also protected by
the rto_lock.
When a CPU schedules in a lower priority task and wants to make sure
overloaded CPUs know about it. It increments the rto_loop_next. Then it
atomically sets rto_loop_start with a cmpxchg. If the old value is not "0",
then it is done, as another CPU is kicking off the IPI loop. If the old
value is "0", then it will take the rto_lock to synchronize with a possible
IPI being sent around to the overloaded CPUs.
If rto_cpu is greater than or equal to nr_cpu_ids, then there's either no
IPI being sent around, or one is about to finish. Then rto_cpu is set to the
first CPU in rto_mask and an IPI is sent to that CPU. If there's no CPUs set
in rto_mask, then there's nothing to be done.
When the CPU receives the IPI, it will first try to push any RT tasks that is
queued on the CPU but can't run because a higher priority RT task is
currently running on that CPU.
Then it takes the rto_lock and looks for the next CPU in the rto_mask. If it
finds one, it simply sends an IPI to that CPU and the process continues.
If there's no more CPUs in the rto_mask, then rto_loop is compared with
rto_loop_next. If they match, everything is done and the process is over. If
they do not match, then a CPU scheduled in a lower priority task as the IPI
was being passed around, and the process needs to start again. The first CPU
in rto_mask is sent the IPI.
This change removes this duplication of work in the IPI logic, and greatly
lowers the latency caused by the IPIs. This removed the lockup happening on
the 120 CPU machine. It also simplifies the code tremendously. What else
could anyone ask for?
Thanks to Peter Zijlstra for simplifying the rto_loop_start atomic logic and
supplying me with the rto_start_trylock() and rto_start_unlock() helper
functions.
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Clark Williams <williams@redhat.com>
Cc: Daniel Bristot de Oliveira <bristot@redhat.com>
Cc: John Kacur <jkacur@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Scott Wood <swood@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20170424114732.1aac6dc4@gandalf.local.home
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-10-06 18:05:04 +00:00
|
|
|
* then the IPI is still running and will continue due to the
|
|
|
|
* update to loop_next, and nothing needs to be done here.
|
|
|
|
* Otherwise it is finishing up and an ipi needs to be sent.
|
|
|
|
*/
|
|
|
|
if (rq->rd->rto_cpu < 0)
|
2018-01-24 01:45:37 +00:00
|
|
|
cpu = rto_next_cpu(rq->rd);
|
sched/rt: Simplify the IPI based RT balancing logic
When a CPU lowers its priority (schedules out a high priority task for a
lower priority one), a check is made to see if any other CPU has overloaded
RT tasks (more than one). It checks the rto_mask to determine this and if so
it will request to pull one of those tasks to itself if the non running RT
task is of higher priority than the new priority of the next task to run on
the current CPU.
When we deal with large number of CPUs, the original pull logic suffered
from large lock contention on a single CPU run queue, which caused a huge
latency across all CPUs. This was caused by only having one CPU having
overloaded RT tasks and a bunch of other CPUs lowering their priority. To
solve this issue, commit:
b6366f048e0c ("sched/rt: Use IPI to trigger RT task push migration instead of pulling")
changed the way to request a pull. Instead of grabbing the lock of the
overloaded CPU's runqueue, it simply sent an IPI to that CPU to do the work.
Although the IPI logic worked very well in removing the large latency build
up, it still could suffer from a large number of IPIs being sent to a single
CPU. On a 80 CPU box, I measured over 200us of processing IPIs. Worse yet,
when I tested this on a 120 CPU box, with a stress test that had lots of
RT tasks scheduling on all CPUs, it actually triggered the hard lockup
detector! One CPU had so many IPIs sent to it, and due to the restart
mechanism that is triggered when the source run queue has a priority status
change, the CPU spent minutes! processing the IPIs.
Thinking about this further, I realized there's no reason for each run queue
to send its own IPI. As all CPUs with overloaded tasks must be scanned
regardless if there's one or many CPUs lowering their priority, because
there's no current way to find the CPU with the highest priority task that
can schedule to one of these CPUs, there really only needs to be one IPI
being sent around at a time.
This greatly simplifies the code!
The new approach is to have each root domain have its own irq work, as the
rto_mask is per root domain. The root domain has the following fields
attached to it:
rto_push_work - the irq work to process each CPU set in rto_mask
rto_lock - the lock to protect some of the other rto fields
rto_loop_start - an atomic that keeps contention down on rto_lock
the first CPU scheduling in a lower priority task
is the one to kick off the process.
rto_loop_next - an atomic that gets incremented for each CPU that
schedules in a lower priority task.
rto_loop - a variable protected by rto_lock that is used to
compare against rto_loop_next
rto_cpu - The cpu to send the next IPI to, also protected by
the rto_lock.
When a CPU schedules in a lower priority task and wants to make sure
overloaded CPUs know about it. It increments the rto_loop_next. Then it
atomically sets rto_loop_start with a cmpxchg. If the old value is not "0",
then it is done, as another CPU is kicking off the IPI loop. If the old
value is "0", then it will take the rto_lock to synchronize with a possible
IPI being sent around to the overloaded CPUs.
If rto_cpu is greater than or equal to nr_cpu_ids, then there's either no
IPI being sent around, or one is about to finish. Then rto_cpu is set to the
first CPU in rto_mask and an IPI is sent to that CPU. If there's no CPUs set
in rto_mask, then there's nothing to be done.
When the CPU receives the IPI, it will first try to push any RT tasks that is
queued on the CPU but can't run because a higher priority RT task is
currently running on that CPU.
Then it takes the rto_lock and looks for the next CPU in the rto_mask. If it
finds one, it simply sends an IPI to that CPU and the process continues.
If there's no more CPUs in the rto_mask, then rto_loop is compared with
rto_loop_next. If they match, everything is done and the process is over. If
they do not match, then a CPU scheduled in a lower priority task as the IPI
was being passed around, and the process needs to start again. The first CPU
in rto_mask is sent the IPI.
This change removes this duplication of work in the IPI logic, and greatly
lowers the latency caused by the IPIs. This removed the lockup happening on
the 120 CPU machine. It also simplifies the code tremendously. What else
could anyone ask for?
Thanks to Peter Zijlstra for simplifying the rto_loop_start atomic logic and
supplying me with the rto_start_trylock() and rto_start_unlock() helper
functions.
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Clark Williams <williams@redhat.com>
Cc: Daniel Bristot de Oliveira <bristot@redhat.com>
Cc: John Kacur <jkacur@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Scott Wood <swood@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20170424114732.1aac6dc4@gandalf.local.home
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-10-06 18:05:04 +00:00
|
|
|
|
|
|
|
raw_spin_unlock(&rq->rd->rto_lock);
|
|
|
|
|
|
|
|
rto_start_unlock(&rq->rd->rto_loop_start);
|
|
|
|
|
2018-01-24 01:45:38 +00:00
|
|
|
if (cpu >= 0) {
|
|
|
|
/* Make sure the rd does not get freed while pushing */
|
|
|
|
sched_get_rd(rq->rd);
|
sched/rt: Simplify the IPI based RT balancing logic
When a CPU lowers its priority (schedules out a high priority task for a
lower priority one), a check is made to see if any other CPU has overloaded
RT tasks (more than one). It checks the rto_mask to determine this and if so
it will request to pull one of those tasks to itself if the non running RT
task is of higher priority than the new priority of the next task to run on
the current CPU.
When we deal with large number of CPUs, the original pull logic suffered
from large lock contention on a single CPU run queue, which caused a huge
latency across all CPUs. This was caused by only having one CPU having
overloaded RT tasks and a bunch of other CPUs lowering their priority. To
solve this issue, commit:
b6366f048e0c ("sched/rt: Use IPI to trigger RT task push migration instead of pulling")
changed the way to request a pull. Instead of grabbing the lock of the
overloaded CPU's runqueue, it simply sent an IPI to that CPU to do the work.
Although the IPI logic worked very well in removing the large latency build
up, it still could suffer from a large number of IPIs being sent to a single
CPU. On a 80 CPU box, I measured over 200us of processing IPIs. Worse yet,
when I tested this on a 120 CPU box, with a stress test that had lots of
RT tasks scheduling on all CPUs, it actually triggered the hard lockup
detector! One CPU had so many IPIs sent to it, and due to the restart
mechanism that is triggered when the source run queue has a priority status
change, the CPU spent minutes! processing the IPIs.
Thinking about this further, I realized there's no reason for each run queue
to send its own IPI. As all CPUs with overloaded tasks must be scanned
regardless if there's one or many CPUs lowering their priority, because
there's no current way to find the CPU with the highest priority task that
can schedule to one of these CPUs, there really only needs to be one IPI
being sent around at a time.
This greatly simplifies the code!
The new approach is to have each root domain have its own irq work, as the
rto_mask is per root domain. The root domain has the following fields
attached to it:
rto_push_work - the irq work to process each CPU set in rto_mask
rto_lock - the lock to protect some of the other rto fields
rto_loop_start - an atomic that keeps contention down on rto_lock
the first CPU scheduling in a lower priority task
is the one to kick off the process.
rto_loop_next - an atomic that gets incremented for each CPU that
schedules in a lower priority task.
rto_loop - a variable protected by rto_lock that is used to
compare against rto_loop_next
rto_cpu - The cpu to send the next IPI to, also protected by
the rto_lock.
When a CPU schedules in a lower priority task and wants to make sure
overloaded CPUs know about it. It increments the rto_loop_next. Then it
atomically sets rto_loop_start with a cmpxchg. If the old value is not "0",
then it is done, as another CPU is kicking off the IPI loop. If the old
value is "0", then it will take the rto_lock to synchronize with a possible
IPI being sent around to the overloaded CPUs.
If rto_cpu is greater than or equal to nr_cpu_ids, then there's either no
IPI being sent around, or one is about to finish. Then rto_cpu is set to the
first CPU in rto_mask and an IPI is sent to that CPU. If there's no CPUs set
in rto_mask, then there's nothing to be done.
When the CPU receives the IPI, it will first try to push any RT tasks that is
queued on the CPU but can't run because a higher priority RT task is
currently running on that CPU.
Then it takes the rto_lock and looks for the next CPU in the rto_mask. If it
finds one, it simply sends an IPI to that CPU and the process continues.
If there's no more CPUs in the rto_mask, then rto_loop is compared with
rto_loop_next. If they match, everything is done and the process is over. If
they do not match, then a CPU scheduled in a lower priority task as the IPI
was being passed around, and the process needs to start again. The first CPU
in rto_mask is sent the IPI.
This change removes this duplication of work in the IPI logic, and greatly
lowers the latency caused by the IPIs. This removed the lockup happening on
the 120 CPU machine. It also simplifies the code tremendously. What else
could anyone ask for?
Thanks to Peter Zijlstra for simplifying the rto_loop_start atomic logic and
supplying me with the rto_start_trylock() and rto_start_unlock() helper
functions.
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Clark Williams <williams@redhat.com>
Cc: Daniel Bristot de Oliveira <bristot@redhat.com>
Cc: John Kacur <jkacur@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Scott Wood <swood@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20170424114732.1aac6dc4@gandalf.local.home
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-10-06 18:05:04 +00:00
|
|
|
irq_work_queue_on(&rq->rd->rto_push_work, cpu);
|
2018-01-24 01:45:38 +00:00
|
|
|
}
|
sched/rt: Use IPI to trigger RT task push migration instead of pulling
When debugging the latencies on a 40 core box, where we hit 300 to
500 microsecond latencies, I found there was a huge contention on the
runqueue locks.
Investigating it further, running ftrace, I found that it was due to
the pulling of RT tasks.
The test that was run was the following:
cyclictest --numa -p95 -m -d0 -i100
This created a thread on each CPU, that would set its wakeup in iterations
of 100 microseconds. The -d0 means that all the threads had the same
interval (100us). Each thread sleeps for 100us and wakes up and measures
its latencies.
cyclictest is maintained at:
git://git.kernel.org/pub/scm/linux/kernel/git/clrkwllms/rt-tests.git
What happened was another RT task would be scheduled on one of the CPUs
that was running our test, when the other CPU tests went to sleep and
scheduled idle. This caused the "pull" operation to execute on all
these CPUs. Each one of these saw the RT task that was overloaded on
the CPU of the test that was still running, and each one tried
to grab that task in a thundering herd way.
To grab the task, each thread would do a double rq lock grab, grabbing
its own lock as well as the rq of the overloaded CPU. As the sched
domains on this box was rather flat for its size, I saw up to 12 CPUs
block on this lock at once. This caused a ripple affect with the
rq locks especially since the taking was done via a double rq lock, which
means that several of the CPUs had their own rq locks held while trying
to take this rq lock. As these locks were blocked, any wakeups or load
balanceing on these CPUs would also block on these locks, and the wait
time escalated.
I've tried various methods to lessen the load, but things like an
atomic counter to only let one CPU grab the task wont work, because
the task may have a limited affinity, and we may pick the wrong
CPU to take that lock and do the pull, to only find out that the
CPU we picked isn't in the task's affinity.
Instead of doing the PULL, I now have the CPUs that want the pull to
send over an IPI to the overloaded CPU, and let that CPU pick what
CPU to push the task to. No more need to grab the rq lock, and the
push/pull algorithm still works fine.
With this patch, the latency dropped to just 150us over a 20 hour run.
Without the patch, the huge latencies would trigger in seconds.
I've created a new sched feature called RT_PUSH_IPI, which is enabled
by default.
When RT_PUSH_IPI is not enabled, the old method of grabbing the rq locks
and having the pulling CPU do the work is implemented. When RT_PUSH_IPI
is enabled, the IPI is sent to the overloaded CPU to do a push.
To enabled or disable this at run time:
# mount -t debugfs nodev /sys/kernel/debug
# echo RT_PUSH_IPI > /sys/kernel/debug/sched_features
or
# echo NO_RT_PUSH_IPI > /sys/kernel/debug/sched_features
Update: This original patch would send an IPI to all CPUs in the RT overload
list. But that could theoretically cause the reverse issue. That is, there
could be lots of overloaded RT queues and one CPU lowers its priority. It would
then send an IPI to all the overloaded RT queues and they could then all try
to grab the rq lock of the CPU lowering its priority, and then we have the
same problem.
The latest design sends out only one IPI to the first overloaded CPU. It tries to
push any tasks that it can, and then looks for the next overloaded CPU that can
push to the source CPU. The IPIs stop when all overloaded CPUs that have pushable
tasks that have priorities greater than the source CPU are covered. In case the
source CPU lowers its priority again, a flag is set to tell the IPI traversal to
restart with the first RT overloaded CPU after the source CPU.
Parts-suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Joern Engel <joern@purestorage.com>
Cc: Clark Williams <williams@redhat.com>
Cc: Mike Galbraith <umgwanakikbuti@gmail.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20150318144946.2f3cc982@gandalf.local.home
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2015-03-18 18:49:46 +00:00
|
|
|
}
|
|
|
|
|
|
|
|
/* Called from hardirq context */
|
sched/rt: Simplify the IPI based RT balancing logic
When a CPU lowers its priority (schedules out a high priority task for a
lower priority one), a check is made to see if any other CPU has overloaded
RT tasks (more than one). It checks the rto_mask to determine this and if so
it will request to pull one of those tasks to itself if the non running RT
task is of higher priority than the new priority of the next task to run on
the current CPU.
When we deal with large number of CPUs, the original pull logic suffered
from large lock contention on a single CPU run queue, which caused a huge
latency across all CPUs. This was caused by only having one CPU having
overloaded RT tasks and a bunch of other CPUs lowering their priority. To
solve this issue, commit:
b6366f048e0c ("sched/rt: Use IPI to trigger RT task push migration instead of pulling")
changed the way to request a pull. Instead of grabbing the lock of the
overloaded CPU's runqueue, it simply sent an IPI to that CPU to do the work.
Although the IPI logic worked very well in removing the large latency build
up, it still could suffer from a large number of IPIs being sent to a single
CPU. On a 80 CPU box, I measured over 200us of processing IPIs. Worse yet,
when I tested this on a 120 CPU box, with a stress test that had lots of
RT tasks scheduling on all CPUs, it actually triggered the hard lockup
detector! One CPU had so many IPIs sent to it, and due to the restart
mechanism that is triggered when the source run queue has a priority status
change, the CPU spent minutes! processing the IPIs.
Thinking about this further, I realized there's no reason for each run queue
to send its own IPI. As all CPUs with overloaded tasks must be scanned
regardless if there's one or many CPUs lowering their priority, because
there's no current way to find the CPU with the highest priority task that
can schedule to one of these CPUs, there really only needs to be one IPI
being sent around at a time.
This greatly simplifies the code!
The new approach is to have each root domain have its own irq work, as the
rto_mask is per root domain. The root domain has the following fields
attached to it:
rto_push_work - the irq work to process each CPU set in rto_mask
rto_lock - the lock to protect some of the other rto fields
rto_loop_start - an atomic that keeps contention down on rto_lock
the first CPU scheduling in a lower priority task
is the one to kick off the process.
rto_loop_next - an atomic that gets incremented for each CPU that
schedules in a lower priority task.
rto_loop - a variable protected by rto_lock that is used to
compare against rto_loop_next
rto_cpu - The cpu to send the next IPI to, also protected by
the rto_lock.
When a CPU schedules in a lower priority task and wants to make sure
overloaded CPUs know about it. It increments the rto_loop_next. Then it
atomically sets rto_loop_start with a cmpxchg. If the old value is not "0",
then it is done, as another CPU is kicking off the IPI loop. If the old
value is "0", then it will take the rto_lock to synchronize with a possible
IPI being sent around to the overloaded CPUs.
If rto_cpu is greater than or equal to nr_cpu_ids, then there's either no
IPI being sent around, or one is about to finish. Then rto_cpu is set to the
first CPU in rto_mask and an IPI is sent to that CPU. If there's no CPUs set
in rto_mask, then there's nothing to be done.
When the CPU receives the IPI, it will first try to push any RT tasks that is
queued on the CPU but can't run because a higher priority RT task is
currently running on that CPU.
Then it takes the rto_lock and looks for the next CPU in the rto_mask. If it
finds one, it simply sends an IPI to that CPU and the process continues.
If there's no more CPUs in the rto_mask, then rto_loop is compared with
rto_loop_next. If they match, everything is done and the process is over. If
they do not match, then a CPU scheduled in a lower priority task as the IPI
was being passed around, and the process needs to start again. The first CPU
in rto_mask is sent the IPI.
This change removes this duplication of work in the IPI logic, and greatly
lowers the latency caused by the IPIs. This removed the lockup happening on
the 120 CPU machine. It also simplifies the code tremendously. What else
could anyone ask for?
Thanks to Peter Zijlstra for simplifying the rto_loop_start atomic logic and
supplying me with the rto_start_trylock() and rto_start_unlock() helper
functions.
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Clark Williams <williams@redhat.com>
Cc: Daniel Bristot de Oliveira <bristot@redhat.com>
Cc: John Kacur <jkacur@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Scott Wood <swood@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20170424114732.1aac6dc4@gandalf.local.home
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-10-06 18:05:04 +00:00
|
|
|
void rto_push_irq_work_func(struct irq_work *work)
|
sched/rt: Use IPI to trigger RT task push migration instead of pulling
When debugging the latencies on a 40 core box, where we hit 300 to
500 microsecond latencies, I found there was a huge contention on the
runqueue locks.
Investigating it further, running ftrace, I found that it was due to
the pulling of RT tasks.
The test that was run was the following:
cyclictest --numa -p95 -m -d0 -i100
This created a thread on each CPU, that would set its wakeup in iterations
of 100 microseconds. The -d0 means that all the threads had the same
interval (100us). Each thread sleeps for 100us and wakes up and measures
its latencies.
cyclictest is maintained at:
git://git.kernel.org/pub/scm/linux/kernel/git/clrkwllms/rt-tests.git
What happened was another RT task would be scheduled on one of the CPUs
that was running our test, when the other CPU tests went to sleep and
scheduled idle. This caused the "pull" operation to execute on all
these CPUs. Each one of these saw the RT task that was overloaded on
the CPU of the test that was still running, and each one tried
to grab that task in a thundering herd way.
To grab the task, each thread would do a double rq lock grab, grabbing
its own lock as well as the rq of the overloaded CPU. As the sched
domains on this box was rather flat for its size, I saw up to 12 CPUs
block on this lock at once. This caused a ripple affect with the
rq locks especially since the taking was done via a double rq lock, which
means that several of the CPUs had their own rq locks held while trying
to take this rq lock. As these locks were blocked, any wakeups or load
balanceing on these CPUs would also block on these locks, and the wait
time escalated.
I've tried various methods to lessen the load, but things like an
atomic counter to only let one CPU grab the task wont work, because
the task may have a limited affinity, and we may pick the wrong
CPU to take that lock and do the pull, to only find out that the
CPU we picked isn't in the task's affinity.
Instead of doing the PULL, I now have the CPUs that want the pull to
send over an IPI to the overloaded CPU, and let that CPU pick what
CPU to push the task to. No more need to grab the rq lock, and the
push/pull algorithm still works fine.
With this patch, the latency dropped to just 150us over a 20 hour run.
Without the patch, the huge latencies would trigger in seconds.
I've created a new sched feature called RT_PUSH_IPI, which is enabled
by default.
When RT_PUSH_IPI is not enabled, the old method of grabbing the rq locks
and having the pulling CPU do the work is implemented. When RT_PUSH_IPI
is enabled, the IPI is sent to the overloaded CPU to do a push.
To enabled or disable this at run time:
# mount -t debugfs nodev /sys/kernel/debug
# echo RT_PUSH_IPI > /sys/kernel/debug/sched_features
or
# echo NO_RT_PUSH_IPI > /sys/kernel/debug/sched_features
Update: This original patch would send an IPI to all CPUs in the RT overload
list. But that could theoretically cause the reverse issue. That is, there
could be lots of overloaded RT queues and one CPU lowers its priority. It would
then send an IPI to all the overloaded RT queues and they could then all try
to grab the rq lock of the CPU lowering its priority, and then we have the
same problem.
The latest design sends out only one IPI to the first overloaded CPU. It tries to
push any tasks that it can, and then looks for the next overloaded CPU that can
push to the source CPU. The IPIs stop when all overloaded CPUs that have pushable
tasks that have priorities greater than the source CPU are covered. In case the
source CPU lowers its priority again, a flag is set to tell the IPI traversal to
restart with the first RT overloaded CPU after the source CPU.
Parts-suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Joern Engel <joern@purestorage.com>
Cc: Clark Williams <williams@redhat.com>
Cc: Mike Galbraith <umgwanakikbuti@gmail.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20150318144946.2f3cc982@gandalf.local.home
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2015-03-18 18:49:46 +00:00
|
|
|
{
|
2018-01-24 01:45:37 +00:00
|
|
|
struct root_domain *rd =
|
|
|
|
container_of(work, struct root_domain, rto_push_work);
|
sched/rt: Simplify the IPI based RT balancing logic
When a CPU lowers its priority (schedules out a high priority task for a
lower priority one), a check is made to see if any other CPU has overloaded
RT tasks (more than one). It checks the rto_mask to determine this and if so
it will request to pull one of those tasks to itself if the non running RT
task is of higher priority than the new priority of the next task to run on
the current CPU.
When we deal with large number of CPUs, the original pull logic suffered
from large lock contention on a single CPU run queue, which caused a huge
latency across all CPUs. This was caused by only having one CPU having
overloaded RT tasks and a bunch of other CPUs lowering their priority. To
solve this issue, commit:
b6366f048e0c ("sched/rt: Use IPI to trigger RT task push migration instead of pulling")
changed the way to request a pull. Instead of grabbing the lock of the
overloaded CPU's runqueue, it simply sent an IPI to that CPU to do the work.
Although the IPI logic worked very well in removing the large latency build
up, it still could suffer from a large number of IPIs being sent to a single
CPU. On a 80 CPU box, I measured over 200us of processing IPIs. Worse yet,
when I tested this on a 120 CPU box, with a stress test that had lots of
RT tasks scheduling on all CPUs, it actually triggered the hard lockup
detector! One CPU had so many IPIs sent to it, and due to the restart
mechanism that is triggered when the source run queue has a priority status
change, the CPU spent minutes! processing the IPIs.
Thinking about this further, I realized there's no reason for each run queue
to send its own IPI. As all CPUs with overloaded tasks must be scanned
regardless if there's one or many CPUs lowering their priority, because
there's no current way to find the CPU with the highest priority task that
can schedule to one of these CPUs, there really only needs to be one IPI
being sent around at a time.
This greatly simplifies the code!
The new approach is to have each root domain have its own irq work, as the
rto_mask is per root domain. The root domain has the following fields
attached to it:
rto_push_work - the irq work to process each CPU set in rto_mask
rto_lock - the lock to protect some of the other rto fields
rto_loop_start - an atomic that keeps contention down on rto_lock
the first CPU scheduling in a lower priority task
is the one to kick off the process.
rto_loop_next - an atomic that gets incremented for each CPU that
schedules in a lower priority task.
rto_loop - a variable protected by rto_lock that is used to
compare against rto_loop_next
rto_cpu - The cpu to send the next IPI to, also protected by
the rto_lock.
When a CPU schedules in a lower priority task and wants to make sure
overloaded CPUs know about it. It increments the rto_loop_next. Then it
atomically sets rto_loop_start with a cmpxchg. If the old value is not "0",
then it is done, as another CPU is kicking off the IPI loop. If the old
value is "0", then it will take the rto_lock to synchronize with a possible
IPI being sent around to the overloaded CPUs.
If rto_cpu is greater than or equal to nr_cpu_ids, then there's either no
IPI being sent around, or one is about to finish. Then rto_cpu is set to the
first CPU in rto_mask and an IPI is sent to that CPU. If there's no CPUs set
in rto_mask, then there's nothing to be done.
When the CPU receives the IPI, it will first try to push any RT tasks that is
queued on the CPU but can't run because a higher priority RT task is
currently running on that CPU.
Then it takes the rto_lock and looks for the next CPU in the rto_mask. If it
finds one, it simply sends an IPI to that CPU and the process continues.
If there's no more CPUs in the rto_mask, then rto_loop is compared with
rto_loop_next. If they match, everything is done and the process is over. If
they do not match, then a CPU scheduled in a lower priority task as the IPI
was being passed around, and the process needs to start again. The first CPU
in rto_mask is sent the IPI.
This change removes this duplication of work in the IPI logic, and greatly
lowers the latency caused by the IPIs. This removed the lockup happening on
the 120 CPU machine. It also simplifies the code tremendously. What else
could anyone ask for?
Thanks to Peter Zijlstra for simplifying the rto_loop_start atomic logic and
supplying me with the rto_start_trylock() and rto_start_unlock() helper
functions.
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Clark Williams <williams@redhat.com>
Cc: Daniel Bristot de Oliveira <bristot@redhat.com>
Cc: John Kacur <jkacur@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Scott Wood <swood@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20170424114732.1aac6dc4@gandalf.local.home
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-10-06 18:05:04 +00:00
|
|
|
struct rq *rq;
|
sched/rt: Use IPI to trigger RT task push migration instead of pulling
When debugging the latencies on a 40 core box, where we hit 300 to
500 microsecond latencies, I found there was a huge contention on the
runqueue locks.
Investigating it further, running ftrace, I found that it was due to
the pulling of RT tasks.
The test that was run was the following:
cyclictest --numa -p95 -m -d0 -i100
This created a thread on each CPU, that would set its wakeup in iterations
of 100 microseconds. The -d0 means that all the threads had the same
interval (100us). Each thread sleeps for 100us and wakes up and measures
its latencies.
cyclictest is maintained at:
git://git.kernel.org/pub/scm/linux/kernel/git/clrkwllms/rt-tests.git
What happened was another RT task would be scheduled on one of the CPUs
that was running our test, when the other CPU tests went to sleep and
scheduled idle. This caused the "pull" operation to execute on all
these CPUs. Each one of these saw the RT task that was overloaded on
the CPU of the test that was still running, and each one tried
to grab that task in a thundering herd way.
To grab the task, each thread would do a double rq lock grab, grabbing
its own lock as well as the rq of the overloaded CPU. As the sched
domains on this box was rather flat for its size, I saw up to 12 CPUs
block on this lock at once. This caused a ripple affect with the
rq locks especially since the taking was done via a double rq lock, which
means that several of the CPUs had their own rq locks held while trying
to take this rq lock. As these locks were blocked, any wakeups or load
balanceing on these CPUs would also block on these locks, and the wait
time escalated.
I've tried various methods to lessen the load, but things like an
atomic counter to only let one CPU grab the task wont work, because
the task may have a limited affinity, and we may pick the wrong
CPU to take that lock and do the pull, to only find out that the
CPU we picked isn't in the task's affinity.
Instead of doing the PULL, I now have the CPUs that want the pull to
send over an IPI to the overloaded CPU, and let that CPU pick what
CPU to push the task to. No more need to grab the rq lock, and the
push/pull algorithm still works fine.
With this patch, the latency dropped to just 150us over a 20 hour run.
Without the patch, the huge latencies would trigger in seconds.
I've created a new sched feature called RT_PUSH_IPI, which is enabled
by default.
When RT_PUSH_IPI is not enabled, the old method of grabbing the rq locks
and having the pulling CPU do the work is implemented. When RT_PUSH_IPI
is enabled, the IPI is sent to the overloaded CPU to do a push.
To enabled or disable this at run time:
# mount -t debugfs nodev /sys/kernel/debug
# echo RT_PUSH_IPI > /sys/kernel/debug/sched_features
or
# echo NO_RT_PUSH_IPI > /sys/kernel/debug/sched_features
Update: This original patch would send an IPI to all CPUs in the RT overload
list. But that could theoretically cause the reverse issue. That is, there
could be lots of overloaded RT queues and one CPU lowers its priority. It would
then send an IPI to all the overloaded RT queues and they could then all try
to grab the rq lock of the CPU lowering its priority, and then we have the
same problem.
The latest design sends out only one IPI to the first overloaded CPU. It tries to
push any tasks that it can, and then looks for the next overloaded CPU that can
push to the source CPU. The IPIs stop when all overloaded CPUs that have pushable
tasks that have priorities greater than the source CPU are covered. In case the
source CPU lowers its priority again, a flag is set to tell the IPI traversal to
restart with the first RT overloaded CPU after the source CPU.
Parts-suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Joern Engel <joern@purestorage.com>
Cc: Clark Williams <williams@redhat.com>
Cc: Mike Galbraith <umgwanakikbuti@gmail.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20150318144946.2f3cc982@gandalf.local.home
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2015-03-18 18:49:46 +00:00
|
|
|
int cpu;
|
|
|
|
|
sched/rt: Simplify the IPI based RT balancing logic
When a CPU lowers its priority (schedules out a high priority task for a
lower priority one), a check is made to see if any other CPU has overloaded
RT tasks (more than one). It checks the rto_mask to determine this and if so
it will request to pull one of those tasks to itself if the non running RT
task is of higher priority than the new priority of the next task to run on
the current CPU.
When we deal with large number of CPUs, the original pull logic suffered
from large lock contention on a single CPU run queue, which caused a huge
latency across all CPUs. This was caused by only having one CPU having
overloaded RT tasks and a bunch of other CPUs lowering their priority. To
solve this issue, commit:
b6366f048e0c ("sched/rt: Use IPI to trigger RT task push migration instead of pulling")
changed the way to request a pull. Instead of grabbing the lock of the
overloaded CPU's runqueue, it simply sent an IPI to that CPU to do the work.
Although the IPI logic worked very well in removing the large latency build
up, it still could suffer from a large number of IPIs being sent to a single
CPU. On a 80 CPU box, I measured over 200us of processing IPIs. Worse yet,
when I tested this on a 120 CPU box, with a stress test that had lots of
RT tasks scheduling on all CPUs, it actually triggered the hard lockup
detector! One CPU had so many IPIs sent to it, and due to the restart
mechanism that is triggered when the source run queue has a priority status
change, the CPU spent minutes! processing the IPIs.
Thinking about this further, I realized there's no reason for each run queue
to send its own IPI. As all CPUs with overloaded tasks must be scanned
regardless if there's one or many CPUs lowering their priority, because
there's no current way to find the CPU with the highest priority task that
can schedule to one of these CPUs, there really only needs to be one IPI
being sent around at a time.
This greatly simplifies the code!
The new approach is to have each root domain have its own irq work, as the
rto_mask is per root domain. The root domain has the following fields
attached to it:
rto_push_work - the irq work to process each CPU set in rto_mask
rto_lock - the lock to protect some of the other rto fields
rto_loop_start - an atomic that keeps contention down on rto_lock
the first CPU scheduling in a lower priority task
is the one to kick off the process.
rto_loop_next - an atomic that gets incremented for each CPU that
schedules in a lower priority task.
rto_loop - a variable protected by rto_lock that is used to
compare against rto_loop_next
rto_cpu - The cpu to send the next IPI to, also protected by
the rto_lock.
When a CPU schedules in a lower priority task and wants to make sure
overloaded CPUs know about it. It increments the rto_loop_next. Then it
atomically sets rto_loop_start with a cmpxchg. If the old value is not "0",
then it is done, as another CPU is kicking off the IPI loop. If the old
value is "0", then it will take the rto_lock to synchronize with a possible
IPI being sent around to the overloaded CPUs.
If rto_cpu is greater than or equal to nr_cpu_ids, then there's either no
IPI being sent around, or one is about to finish. Then rto_cpu is set to the
first CPU in rto_mask and an IPI is sent to that CPU. If there's no CPUs set
in rto_mask, then there's nothing to be done.
When the CPU receives the IPI, it will first try to push any RT tasks that is
queued on the CPU but can't run because a higher priority RT task is
currently running on that CPU.
Then it takes the rto_lock and looks for the next CPU in the rto_mask. If it
finds one, it simply sends an IPI to that CPU and the process continues.
If there's no more CPUs in the rto_mask, then rto_loop is compared with
rto_loop_next. If they match, everything is done and the process is over. If
they do not match, then a CPU scheduled in a lower priority task as the IPI
was being passed around, and the process needs to start again. The first CPU
in rto_mask is sent the IPI.
This change removes this duplication of work in the IPI logic, and greatly
lowers the latency caused by the IPIs. This removed the lockup happening on
the 120 CPU machine. It also simplifies the code tremendously. What else
could anyone ask for?
Thanks to Peter Zijlstra for simplifying the rto_loop_start atomic logic and
supplying me with the rto_start_trylock() and rto_start_unlock() helper
functions.
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Clark Williams <williams@redhat.com>
Cc: Daniel Bristot de Oliveira <bristot@redhat.com>
Cc: John Kacur <jkacur@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Scott Wood <swood@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20170424114732.1aac6dc4@gandalf.local.home
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-10-06 18:05:04 +00:00
|
|
|
rq = this_rq();
|
sched/rt: Use IPI to trigger RT task push migration instead of pulling
When debugging the latencies on a 40 core box, where we hit 300 to
500 microsecond latencies, I found there was a huge contention on the
runqueue locks.
Investigating it further, running ftrace, I found that it was due to
the pulling of RT tasks.
The test that was run was the following:
cyclictest --numa -p95 -m -d0 -i100
This created a thread on each CPU, that would set its wakeup in iterations
of 100 microseconds. The -d0 means that all the threads had the same
interval (100us). Each thread sleeps for 100us and wakes up and measures
its latencies.
cyclictest is maintained at:
git://git.kernel.org/pub/scm/linux/kernel/git/clrkwllms/rt-tests.git
What happened was another RT task would be scheduled on one of the CPUs
that was running our test, when the other CPU tests went to sleep and
scheduled idle. This caused the "pull" operation to execute on all
these CPUs. Each one of these saw the RT task that was overloaded on
the CPU of the test that was still running, and each one tried
to grab that task in a thundering herd way.
To grab the task, each thread would do a double rq lock grab, grabbing
its own lock as well as the rq of the overloaded CPU. As the sched
domains on this box was rather flat for its size, I saw up to 12 CPUs
block on this lock at once. This caused a ripple affect with the
rq locks especially since the taking was done via a double rq lock, which
means that several of the CPUs had their own rq locks held while trying
to take this rq lock. As these locks were blocked, any wakeups or load
balanceing on these CPUs would also block on these locks, and the wait
time escalated.
I've tried various methods to lessen the load, but things like an
atomic counter to only let one CPU grab the task wont work, because
the task may have a limited affinity, and we may pick the wrong
CPU to take that lock and do the pull, to only find out that the
CPU we picked isn't in the task's affinity.
Instead of doing the PULL, I now have the CPUs that want the pull to
send over an IPI to the overloaded CPU, and let that CPU pick what
CPU to push the task to. No more need to grab the rq lock, and the
push/pull algorithm still works fine.
With this patch, the latency dropped to just 150us over a 20 hour run.
Without the patch, the huge latencies would trigger in seconds.
I've created a new sched feature called RT_PUSH_IPI, which is enabled
by default.
When RT_PUSH_IPI is not enabled, the old method of grabbing the rq locks
and having the pulling CPU do the work is implemented. When RT_PUSH_IPI
is enabled, the IPI is sent to the overloaded CPU to do a push.
To enabled or disable this at run time:
# mount -t debugfs nodev /sys/kernel/debug
# echo RT_PUSH_IPI > /sys/kernel/debug/sched_features
or
# echo NO_RT_PUSH_IPI > /sys/kernel/debug/sched_features
Update: This original patch would send an IPI to all CPUs in the RT overload
list. But that could theoretically cause the reverse issue. That is, there
could be lots of overloaded RT queues and one CPU lowers its priority. It would
then send an IPI to all the overloaded RT queues and they could then all try
to grab the rq lock of the CPU lowering its priority, and then we have the
same problem.
The latest design sends out only one IPI to the first overloaded CPU. It tries to
push any tasks that it can, and then looks for the next overloaded CPU that can
push to the source CPU. The IPIs stop when all overloaded CPUs that have pushable
tasks that have priorities greater than the source CPU are covered. In case the
source CPU lowers its priority again, a flag is set to tell the IPI traversal to
restart with the first RT overloaded CPU after the source CPU.
Parts-suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Joern Engel <joern@purestorage.com>
Cc: Clark Williams <williams@redhat.com>
Cc: Mike Galbraith <umgwanakikbuti@gmail.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20150318144946.2f3cc982@gandalf.local.home
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2015-03-18 18:49:46 +00:00
|
|
|
|
sched/rt: Simplify the IPI based RT balancing logic
When a CPU lowers its priority (schedules out a high priority task for a
lower priority one), a check is made to see if any other CPU has overloaded
RT tasks (more than one). It checks the rto_mask to determine this and if so
it will request to pull one of those tasks to itself if the non running RT
task is of higher priority than the new priority of the next task to run on
the current CPU.
When we deal with large number of CPUs, the original pull logic suffered
from large lock contention on a single CPU run queue, which caused a huge
latency across all CPUs. This was caused by only having one CPU having
overloaded RT tasks and a bunch of other CPUs lowering their priority. To
solve this issue, commit:
b6366f048e0c ("sched/rt: Use IPI to trigger RT task push migration instead of pulling")
changed the way to request a pull. Instead of grabbing the lock of the
overloaded CPU's runqueue, it simply sent an IPI to that CPU to do the work.
Although the IPI logic worked very well in removing the large latency build
up, it still could suffer from a large number of IPIs being sent to a single
CPU. On a 80 CPU box, I measured over 200us of processing IPIs. Worse yet,
when I tested this on a 120 CPU box, with a stress test that had lots of
RT tasks scheduling on all CPUs, it actually triggered the hard lockup
detector! One CPU had so many IPIs sent to it, and due to the restart
mechanism that is triggered when the source run queue has a priority status
change, the CPU spent minutes! processing the IPIs.
Thinking about this further, I realized there's no reason for each run queue
to send its own IPI. As all CPUs with overloaded tasks must be scanned
regardless if there's one or many CPUs lowering their priority, because
there's no current way to find the CPU with the highest priority task that
can schedule to one of these CPUs, there really only needs to be one IPI
being sent around at a time.
This greatly simplifies the code!
The new approach is to have each root domain have its own irq work, as the
rto_mask is per root domain. The root domain has the following fields
attached to it:
rto_push_work - the irq work to process each CPU set in rto_mask
rto_lock - the lock to protect some of the other rto fields
rto_loop_start - an atomic that keeps contention down on rto_lock
the first CPU scheduling in a lower priority task
is the one to kick off the process.
rto_loop_next - an atomic that gets incremented for each CPU that
schedules in a lower priority task.
rto_loop - a variable protected by rto_lock that is used to
compare against rto_loop_next
rto_cpu - The cpu to send the next IPI to, also protected by
the rto_lock.
When a CPU schedules in a lower priority task and wants to make sure
overloaded CPUs know about it. It increments the rto_loop_next. Then it
atomically sets rto_loop_start with a cmpxchg. If the old value is not "0",
then it is done, as another CPU is kicking off the IPI loop. If the old
value is "0", then it will take the rto_lock to synchronize with a possible
IPI being sent around to the overloaded CPUs.
If rto_cpu is greater than or equal to nr_cpu_ids, then there's either no
IPI being sent around, or one is about to finish. Then rto_cpu is set to the
first CPU in rto_mask and an IPI is sent to that CPU. If there's no CPUs set
in rto_mask, then there's nothing to be done.
When the CPU receives the IPI, it will first try to push any RT tasks that is
queued on the CPU but can't run because a higher priority RT task is
currently running on that CPU.
Then it takes the rto_lock and looks for the next CPU in the rto_mask. If it
finds one, it simply sends an IPI to that CPU and the process continues.
If there's no more CPUs in the rto_mask, then rto_loop is compared with
rto_loop_next. If they match, everything is done and the process is over. If
they do not match, then a CPU scheduled in a lower priority task as the IPI
was being passed around, and the process needs to start again. The first CPU
in rto_mask is sent the IPI.
This change removes this duplication of work in the IPI logic, and greatly
lowers the latency caused by the IPIs. This removed the lockup happening on
the 120 CPU machine. It also simplifies the code tremendously. What else
could anyone ask for?
Thanks to Peter Zijlstra for simplifying the rto_loop_start atomic logic and
supplying me with the rto_start_trylock() and rto_start_unlock() helper
functions.
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Clark Williams <williams@redhat.com>
Cc: Daniel Bristot de Oliveira <bristot@redhat.com>
Cc: John Kacur <jkacur@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Scott Wood <swood@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20170424114732.1aac6dc4@gandalf.local.home
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-10-06 18:05:04 +00:00
|
|
|
/*
|
|
|
|
* We do not need to grab the lock to check for has_pushable_tasks.
|
|
|
|
* When it gets updated, a check is made if a push is possible.
|
|
|
|
*/
|
sched/rt: Use IPI to trigger RT task push migration instead of pulling
When debugging the latencies on a 40 core box, where we hit 300 to
500 microsecond latencies, I found there was a huge contention on the
runqueue locks.
Investigating it further, running ftrace, I found that it was due to
the pulling of RT tasks.
The test that was run was the following:
cyclictest --numa -p95 -m -d0 -i100
This created a thread on each CPU, that would set its wakeup in iterations
of 100 microseconds. The -d0 means that all the threads had the same
interval (100us). Each thread sleeps for 100us and wakes up and measures
its latencies.
cyclictest is maintained at:
git://git.kernel.org/pub/scm/linux/kernel/git/clrkwllms/rt-tests.git
What happened was another RT task would be scheduled on one of the CPUs
that was running our test, when the other CPU tests went to sleep and
scheduled idle. This caused the "pull" operation to execute on all
these CPUs. Each one of these saw the RT task that was overloaded on
the CPU of the test that was still running, and each one tried
to grab that task in a thundering herd way.
To grab the task, each thread would do a double rq lock grab, grabbing
its own lock as well as the rq of the overloaded CPU. As the sched
domains on this box was rather flat for its size, I saw up to 12 CPUs
block on this lock at once. This caused a ripple affect with the
rq locks especially since the taking was done via a double rq lock, which
means that several of the CPUs had their own rq locks held while trying
to take this rq lock. As these locks were blocked, any wakeups or load
balanceing on these CPUs would also block on these locks, and the wait
time escalated.
I've tried various methods to lessen the load, but things like an
atomic counter to only let one CPU grab the task wont work, because
the task may have a limited affinity, and we may pick the wrong
CPU to take that lock and do the pull, to only find out that the
CPU we picked isn't in the task's affinity.
Instead of doing the PULL, I now have the CPUs that want the pull to
send over an IPI to the overloaded CPU, and let that CPU pick what
CPU to push the task to. No more need to grab the rq lock, and the
push/pull algorithm still works fine.
With this patch, the latency dropped to just 150us over a 20 hour run.
Without the patch, the huge latencies would trigger in seconds.
I've created a new sched feature called RT_PUSH_IPI, which is enabled
by default.
When RT_PUSH_IPI is not enabled, the old method of grabbing the rq locks
and having the pulling CPU do the work is implemented. When RT_PUSH_IPI
is enabled, the IPI is sent to the overloaded CPU to do a push.
To enabled or disable this at run time:
# mount -t debugfs nodev /sys/kernel/debug
# echo RT_PUSH_IPI > /sys/kernel/debug/sched_features
or
# echo NO_RT_PUSH_IPI > /sys/kernel/debug/sched_features
Update: This original patch would send an IPI to all CPUs in the RT overload
list. But that could theoretically cause the reverse issue. That is, there
could be lots of overloaded RT queues and one CPU lowers its priority. It would
then send an IPI to all the overloaded RT queues and they could then all try
to grab the rq lock of the CPU lowering its priority, and then we have the
same problem.
The latest design sends out only one IPI to the first overloaded CPU. It tries to
push any tasks that it can, and then looks for the next overloaded CPU that can
push to the source CPU. The IPIs stop when all overloaded CPUs that have pushable
tasks that have priorities greater than the source CPU are covered. In case the
source CPU lowers its priority again, a flag is set to tell the IPI traversal to
restart with the first RT overloaded CPU after the source CPU.
Parts-suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Joern Engel <joern@purestorage.com>
Cc: Clark Williams <williams@redhat.com>
Cc: Mike Galbraith <umgwanakikbuti@gmail.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20150318144946.2f3cc982@gandalf.local.home
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2015-03-18 18:49:46 +00:00
|
|
|
if (has_pushable_tasks(rq)) {
|
2020-11-17 23:19:31 +00:00
|
|
|
raw_spin_rq_lock(rq);
|
2020-09-28 15:06:07 +00:00
|
|
|
while (push_rt_task(rq, true))
|
|
|
|
;
|
2020-11-17 23:19:31 +00:00
|
|
|
raw_spin_rq_unlock(rq);
|
sched/rt: Use IPI to trigger RT task push migration instead of pulling
When debugging the latencies on a 40 core box, where we hit 300 to
500 microsecond latencies, I found there was a huge contention on the
runqueue locks.
Investigating it further, running ftrace, I found that it was due to
the pulling of RT tasks.
The test that was run was the following:
cyclictest --numa -p95 -m -d0 -i100
This created a thread on each CPU, that would set its wakeup in iterations
of 100 microseconds. The -d0 means that all the threads had the same
interval (100us). Each thread sleeps for 100us and wakes up and measures
its latencies.
cyclictest is maintained at:
git://git.kernel.org/pub/scm/linux/kernel/git/clrkwllms/rt-tests.git
What happened was another RT task would be scheduled on one of the CPUs
that was running our test, when the other CPU tests went to sleep and
scheduled idle. This caused the "pull" operation to execute on all
these CPUs. Each one of these saw the RT task that was overloaded on
the CPU of the test that was still running, and each one tried
to grab that task in a thundering herd way.
To grab the task, each thread would do a double rq lock grab, grabbing
its own lock as well as the rq of the overloaded CPU. As the sched
domains on this box was rather flat for its size, I saw up to 12 CPUs
block on this lock at once. This caused a ripple affect with the
rq locks especially since the taking was done via a double rq lock, which
means that several of the CPUs had their own rq locks held while trying
to take this rq lock. As these locks were blocked, any wakeups or load
balanceing on these CPUs would also block on these locks, and the wait
time escalated.
I've tried various methods to lessen the load, but things like an
atomic counter to only let one CPU grab the task wont work, because
the task may have a limited affinity, and we may pick the wrong
CPU to take that lock and do the pull, to only find out that the
CPU we picked isn't in the task's affinity.
Instead of doing the PULL, I now have the CPUs that want the pull to
send over an IPI to the overloaded CPU, and let that CPU pick what
CPU to push the task to. No more need to grab the rq lock, and the
push/pull algorithm still works fine.
With this patch, the latency dropped to just 150us over a 20 hour run.
Without the patch, the huge latencies would trigger in seconds.
I've created a new sched feature called RT_PUSH_IPI, which is enabled
by default.
When RT_PUSH_IPI is not enabled, the old method of grabbing the rq locks
and having the pulling CPU do the work is implemented. When RT_PUSH_IPI
is enabled, the IPI is sent to the overloaded CPU to do a push.
To enabled or disable this at run time:
# mount -t debugfs nodev /sys/kernel/debug
# echo RT_PUSH_IPI > /sys/kernel/debug/sched_features
or
# echo NO_RT_PUSH_IPI > /sys/kernel/debug/sched_features
Update: This original patch would send an IPI to all CPUs in the RT overload
list. But that could theoretically cause the reverse issue. That is, there
could be lots of overloaded RT queues and one CPU lowers its priority. It would
then send an IPI to all the overloaded RT queues and they could then all try
to grab the rq lock of the CPU lowering its priority, and then we have the
same problem.
The latest design sends out only one IPI to the first overloaded CPU. It tries to
push any tasks that it can, and then looks for the next overloaded CPU that can
push to the source CPU. The IPIs stop when all overloaded CPUs that have pushable
tasks that have priorities greater than the source CPU are covered. In case the
source CPU lowers its priority again, a flag is set to tell the IPI traversal to
restart with the first RT overloaded CPU after the source CPU.
Parts-suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Joern Engel <joern@purestorage.com>
Cc: Clark Williams <williams@redhat.com>
Cc: Mike Galbraith <umgwanakikbuti@gmail.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20150318144946.2f3cc982@gandalf.local.home
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2015-03-18 18:49:46 +00:00
|
|
|
}
|
|
|
|
|
2018-01-24 01:45:37 +00:00
|
|
|
raw_spin_lock(&rd->rto_lock);
|
sched/rt: Use IPI to trigger RT task push migration instead of pulling
When debugging the latencies on a 40 core box, where we hit 300 to
500 microsecond latencies, I found there was a huge contention on the
runqueue locks.
Investigating it further, running ftrace, I found that it was due to
the pulling of RT tasks.
The test that was run was the following:
cyclictest --numa -p95 -m -d0 -i100
This created a thread on each CPU, that would set its wakeup in iterations
of 100 microseconds. The -d0 means that all the threads had the same
interval (100us). Each thread sleeps for 100us and wakes up and measures
its latencies.
cyclictest is maintained at:
git://git.kernel.org/pub/scm/linux/kernel/git/clrkwllms/rt-tests.git
What happened was another RT task would be scheduled on one of the CPUs
that was running our test, when the other CPU tests went to sleep and
scheduled idle. This caused the "pull" operation to execute on all
these CPUs. Each one of these saw the RT task that was overloaded on
the CPU of the test that was still running, and each one tried
to grab that task in a thundering herd way.
To grab the task, each thread would do a double rq lock grab, grabbing
its own lock as well as the rq of the overloaded CPU. As the sched
domains on this box was rather flat for its size, I saw up to 12 CPUs
block on this lock at once. This caused a ripple affect with the
rq locks especially since the taking was done via a double rq lock, which
means that several of the CPUs had their own rq locks held while trying
to take this rq lock. As these locks were blocked, any wakeups or load
balanceing on these CPUs would also block on these locks, and the wait
time escalated.
I've tried various methods to lessen the load, but things like an
atomic counter to only let one CPU grab the task wont work, because
the task may have a limited affinity, and we may pick the wrong
CPU to take that lock and do the pull, to only find out that the
CPU we picked isn't in the task's affinity.
Instead of doing the PULL, I now have the CPUs that want the pull to
send over an IPI to the overloaded CPU, and let that CPU pick what
CPU to push the task to. No more need to grab the rq lock, and the
push/pull algorithm still works fine.
With this patch, the latency dropped to just 150us over a 20 hour run.
Without the patch, the huge latencies would trigger in seconds.
I've created a new sched feature called RT_PUSH_IPI, which is enabled
by default.
When RT_PUSH_IPI is not enabled, the old method of grabbing the rq locks
and having the pulling CPU do the work is implemented. When RT_PUSH_IPI
is enabled, the IPI is sent to the overloaded CPU to do a push.
To enabled or disable this at run time:
# mount -t debugfs nodev /sys/kernel/debug
# echo RT_PUSH_IPI > /sys/kernel/debug/sched_features
or
# echo NO_RT_PUSH_IPI > /sys/kernel/debug/sched_features
Update: This original patch would send an IPI to all CPUs in the RT overload
list. But that could theoretically cause the reverse issue. That is, there
could be lots of overloaded RT queues and one CPU lowers its priority. It would
then send an IPI to all the overloaded RT queues and they could then all try
to grab the rq lock of the CPU lowering its priority, and then we have the
same problem.
The latest design sends out only one IPI to the first overloaded CPU. It tries to
push any tasks that it can, and then looks for the next overloaded CPU that can
push to the source CPU. The IPIs stop when all overloaded CPUs that have pushable
tasks that have priorities greater than the source CPU are covered. In case the
source CPU lowers its priority again, a flag is set to tell the IPI traversal to
restart with the first RT overloaded CPU after the source CPU.
Parts-suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Joern Engel <joern@purestorage.com>
Cc: Clark Williams <williams@redhat.com>
Cc: Mike Galbraith <umgwanakikbuti@gmail.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20150318144946.2f3cc982@gandalf.local.home
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2015-03-18 18:49:46 +00:00
|
|
|
|
sched/rt: Simplify the IPI based RT balancing logic
When a CPU lowers its priority (schedules out a high priority task for a
lower priority one), a check is made to see if any other CPU has overloaded
RT tasks (more than one). It checks the rto_mask to determine this and if so
it will request to pull one of those tasks to itself if the non running RT
task is of higher priority than the new priority of the next task to run on
the current CPU.
When we deal with large number of CPUs, the original pull logic suffered
from large lock contention on a single CPU run queue, which caused a huge
latency across all CPUs. This was caused by only having one CPU having
overloaded RT tasks and a bunch of other CPUs lowering their priority. To
solve this issue, commit:
b6366f048e0c ("sched/rt: Use IPI to trigger RT task push migration instead of pulling")
changed the way to request a pull. Instead of grabbing the lock of the
overloaded CPU's runqueue, it simply sent an IPI to that CPU to do the work.
Although the IPI logic worked very well in removing the large latency build
up, it still could suffer from a large number of IPIs being sent to a single
CPU. On a 80 CPU box, I measured over 200us of processing IPIs. Worse yet,
when I tested this on a 120 CPU box, with a stress test that had lots of
RT tasks scheduling on all CPUs, it actually triggered the hard lockup
detector! One CPU had so many IPIs sent to it, and due to the restart
mechanism that is triggered when the source run queue has a priority status
change, the CPU spent minutes! processing the IPIs.
Thinking about this further, I realized there's no reason for each run queue
to send its own IPI. As all CPUs with overloaded tasks must be scanned
regardless if there's one or many CPUs lowering their priority, because
there's no current way to find the CPU with the highest priority task that
can schedule to one of these CPUs, there really only needs to be one IPI
being sent around at a time.
This greatly simplifies the code!
The new approach is to have each root domain have its own irq work, as the
rto_mask is per root domain. The root domain has the following fields
attached to it:
rto_push_work - the irq work to process each CPU set in rto_mask
rto_lock - the lock to protect some of the other rto fields
rto_loop_start - an atomic that keeps contention down on rto_lock
the first CPU scheduling in a lower priority task
is the one to kick off the process.
rto_loop_next - an atomic that gets incremented for each CPU that
schedules in a lower priority task.
rto_loop - a variable protected by rto_lock that is used to
compare against rto_loop_next
rto_cpu - The cpu to send the next IPI to, also protected by
the rto_lock.
When a CPU schedules in a lower priority task and wants to make sure
overloaded CPUs know about it. It increments the rto_loop_next. Then it
atomically sets rto_loop_start with a cmpxchg. If the old value is not "0",
then it is done, as another CPU is kicking off the IPI loop. If the old
value is "0", then it will take the rto_lock to synchronize with a possible
IPI being sent around to the overloaded CPUs.
If rto_cpu is greater than or equal to nr_cpu_ids, then there's either no
IPI being sent around, or one is about to finish. Then rto_cpu is set to the
first CPU in rto_mask and an IPI is sent to that CPU. If there's no CPUs set
in rto_mask, then there's nothing to be done.
When the CPU receives the IPI, it will first try to push any RT tasks that is
queued on the CPU but can't run because a higher priority RT task is
currently running on that CPU.
Then it takes the rto_lock and looks for the next CPU in the rto_mask. If it
finds one, it simply sends an IPI to that CPU and the process continues.
If there's no more CPUs in the rto_mask, then rto_loop is compared with
rto_loop_next. If they match, everything is done and the process is over. If
they do not match, then a CPU scheduled in a lower priority task as the IPI
was being passed around, and the process needs to start again. The first CPU
in rto_mask is sent the IPI.
This change removes this duplication of work in the IPI logic, and greatly
lowers the latency caused by the IPIs. This removed the lockup happening on
the 120 CPU machine. It also simplifies the code tremendously. What else
could anyone ask for?
Thanks to Peter Zijlstra for simplifying the rto_loop_start atomic logic and
supplying me with the rto_start_trylock() and rto_start_unlock() helper
functions.
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Clark Williams <williams@redhat.com>
Cc: Daniel Bristot de Oliveira <bristot@redhat.com>
Cc: John Kacur <jkacur@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Scott Wood <swood@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20170424114732.1aac6dc4@gandalf.local.home
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-10-06 18:05:04 +00:00
|
|
|
/* Pass the IPI to the next rt overloaded queue */
|
2018-01-24 01:45:37 +00:00
|
|
|
cpu = rto_next_cpu(rd);
|
sched/rt: Use IPI to trigger RT task push migration instead of pulling
When debugging the latencies on a 40 core box, where we hit 300 to
500 microsecond latencies, I found there was a huge contention on the
runqueue locks.
Investigating it further, running ftrace, I found that it was due to
the pulling of RT tasks.
The test that was run was the following:
cyclictest --numa -p95 -m -d0 -i100
This created a thread on each CPU, that would set its wakeup in iterations
of 100 microseconds. The -d0 means that all the threads had the same
interval (100us). Each thread sleeps for 100us and wakes up and measures
its latencies.
cyclictest is maintained at:
git://git.kernel.org/pub/scm/linux/kernel/git/clrkwllms/rt-tests.git
What happened was another RT task would be scheduled on one of the CPUs
that was running our test, when the other CPU tests went to sleep and
scheduled idle. This caused the "pull" operation to execute on all
these CPUs. Each one of these saw the RT task that was overloaded on
the CPU of the test that was still running, and each one tried
to grab that task in a thundering herd way.
To grab the task, each thread would do a double rq lock grab, grabbing
its own lock as well as the rq of the overloaded CPU. As the sched
domains on this box was rather flat for its size, I saw up to 12 CPUs
block on this lock at once. This caused a ripple affect with the
rq locks especially since the taking was done via a double rq lock, which
means that several of the CPUs had their own rq locks held while trying
to take this rq lock. As these locks were blocked, any wakeups or load
balanceing on these CPUs would also block on these locks, and the wait
time escalated.
I've tried various methods to lessen the load, but things like an
atomic counter to only let one CPU grab the task wont work, because
the task may have a limited affinity, and we may pick the wrong
CPU to take that lock and do the pull, to only find out that the
CPU we picked isn't in the task's affinity.
Instead of doing the PULL, I now have the CPUs that want the pull to
send over an IPI to the overloaded CPU, and let that CPU pick what
CPU to push the task to. No more need to grab the rq lock, and the
push/pull algorithm still works fine.
With this patch, the latency dropped to just 150us over a 20 hour run.
Without the patch, the huge latencies would trigger in seconds.
I've created a new sched feature called RT_PUSH_IPI, which is enabled
by default.
When RT_PUSH_IPI is not enabled, the old method of grabbing the rq locks
and having the pulling CPU do the work is implemented. When RT_PUSH_IPI
is enabled, the IPI is sent to the overloaded CPU to do a push.
To enabled or disable this at run time:
# mount -t debugfs nodev /sys/kernel/debug
# echo RT_PUSH_IPI > /sys/kernel/debug/sched_features
or
# echo NO_RT_PUSH_IPI > /sys/kernel/debug/sched_features
Update: This original patch would send an IPI to all CPUs in the RT overload
list. But that could theoretically cause the reverse issue. That is, there
could be lots of overloaded RT queues and one CPU lowers its priority. It would
then send an IPI to all the overloaded RT queues and they could then all try
to grab the rq lock of the CPU lowering its priority, and then we have the
same problem.
The latest design sends out only one IPI to the first overloaded CPU. It tries to
push any tasks that it can, and then looks for the next overloaded CPU that can
push to the source CPU. The IPIs stop when all overloaded CPUs that have pushable
tasks that have priorities greater than the source CPU are covered. In case the
source CPU lowers its priority again, a flag is set to tell the IPI traversal to
restart with the first RT overloaded CPU after the source CPU.
Parts-suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Joern Engel <joern@purestorage.com>
Cc: Clark Williams <williams@redhat.com>
Cc: Mike Galbraith <umgwanakikbuti@gmail.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20150318144946.2f3cc982@gandalf.local.home
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2015-03-18 18:49:46 +00:00
|
|
|
|
2018-01-24 01:45:37 +00:00
|
|
|
raw_spin_unlock(&rd->rto_lock);
|
sched/rt: Use IPI to trigger RT task push migration instead of pulling
When debugging the latencies on a 40 core box, where we hit 300 to
500 microsecond latencies, I found there was a huge contention on the
runqueue locks.
Investigating it further, running ftrace, I found that it was due to
the pulling of RT tasks.
The test that was run was the following:
cyclictest --numa -p95 -m -d0 -i100
This created a thread on each CPU, that would set its wakeup in iterations
of 100 microseconds. The -d0 means that all the threads had the same
interval (100us). Each thread sleeps for 100us and wakes up and measures
its latencies.
cyclictest is maintained at:
git://git.kernel.org/pub/scm/linux/kernel/git/clrkwllms/rt-tests.git
What happened was another RT task would be scheduled on one of the CPUs
that was running our test, when the other CPU tests went to sleep and
scheduled idle. This caused the "pull" operation to execute on all
these CPUs. Each one of these saw the RT task that was overloaded on
the CPU of the test that was still running, and each one tried
to grab that task in a thundering herd way.
To grab the task, each thread would do a double rq lock grab, grabbing
its own lock as well as the rq of the overloaded CPU. As the sched
domains on this box was rather flat for its size, I saw up to 12 CPUs
block on this lock at once. This caused a ripple affect with the
rq locks especially since the taking was done via a double rq lock, which
means that several of the CPUs had their own rq locks held while trying
to take this rq lock. As these locks were blocked, any wakeups or load
balanceing on these CPUs would also block on these locks, and the wait
time escalated.
I've tried various methods to lessen the load, but things like an
atomic counter to only let one CPU grab the task wont work, because
the task may have a limited affinity, and we may pick the wrong
CPU to take that lock and do the pull, to only find out that the
CPU we picked isn't in the task's affinity.
Instead of doing the PULL, I now have the CPUs that want the pull to
send over an IPI to the overloaded CPU, and let that CPU pick what
CPU to push the task to. No more need to grab the rq lock, and the
push/pull algorithm still works fine.
With this patch, the latency dropped to just 150us over a 20 hour run.
Without the patch, the huge latencies would trigger in seconds.
I've created a new sched feature called RT_PUSH_IPI, which is enabled
by default.
When RT_PUSH_IPI is not enabled, the old method of grabbing the rq locks
and having the pulling CPU do the work is implemented. When RT_PUSH_IPI
is enabled, the IPI is sent to the overloaded CPU to do a push.
To enabled or disable this at run time:
# mount -t debugfs nodev /sys/kernel/debug
# echo RT_PUSH_IPI > /sys/kernel/debug/sched_features
or
# echo NO_RT_PUSH_IPI > /sys/kernel/debug/sched_features
Update: This original patch would send an IPI to all CPUs in the RT overload
list. But that could theoretically cause the reverse issue. That is, there
could be lots of overloaded RT queues and one CPU lowers its priority. It would
then send an IPI to all the overloaded RT queues and they could then all try
to grab the rq lock of the CPU lowering its priority, and then we have the
same problem.
The latest design sends out only one IPI to the first overloaded CPU. It tries to
push any tasks that it can, and then looks for the next overloaded CPU that can
push to the source CPU. The IPIs stop when all overloaded CPUs that have pushable
tasks that have priorities greater than the source CPU are covered. In case the
source CPU lowers its priority again, a flag is set to tell the IPI traversal to
restart with the first RT overloaded CPU after the source CPU.
Parts-suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Joern Engel <joern@purestorage.com>
Cc: Clark Williams <williams@redhat.com>
Cc: Mike Galbraith <umgwanakikbuti@gmail.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20150318144946.2f3cc982@gandalf.local.home
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2015-03-18 18:49:46 +00:00
|
|
|
|
2018-01-24 01:45:38 +00:00
|
|
|
if (cpu < 0) {
|
|
|
|
sched_put_rd(rd);
|
sched/rt: Use IPI to trigger RT task push migration instead of pulling
When debugging the latencies on a 40 core box, where we hit 300 to
500 microsecond latencies, I found there was a huge contention on the
runqueue locks.
Investigating it further, running ftrace, I found that it was due to
the pulling of RT tasks.
The test that was run was the following:
cyclictest --numa -p95 -m -d0 -i100
This created a thread on each CPU, that would set its wakeup in iterations
of 100 microseconds. The -d0 means that all the threads had the same
interval (100us). Each thread sleeps for 100us and wakes up and measures
its latencies.
cyclictest is maintained at:
git://git.kernel.org/pub/scm/linux/kernel/git/clrkwllms/rt-tests.git
What happened was another RT task would be scheduled on one of the CPUs
that was running our test, when the other CPU tests went to sleep and
scheduled idle. This caused the "pull" operation to execute on all
these CPUs. Each one of these saw the RT task that was overloaded on
the CPU of the test that was still running, and each one tried
to grab that task in a thundering herd way.
To grab the task, each thread would do a double rq lock grab, grabbing
its own lock as well as the rq of the overloaded CPU. As the sched
domains on this box was rather flat for its size, I saw up to 12 CPUs
block on this lock at once. This caused a ripple affect with the
rq locks especially since the taking was done via a double rq lock, which
means that several of the CPUs had their own rq locks held while trying
to take this rq lock. As these locks were blocked, any wakeups or load
balanceing on these CPUs would also block on these locks, and the wait
time escalated.
I've tried various methods to lessen the load, but things like an
atomic counter to only let one CPU grab the task wont work, because
the task may have a limited affinity, and we may pick the wrong
CPU to take that lock and do the pull, to only find out that the
CPU we picked isn't in the task's affinity.
Instead of doing the PULL, I now have the CPUs that want the pull to
send over an IPI to the overloaded CPU, and let that CPU pick what
CPU to push the task to. No more need to grab the rq lock, and the
push/pull algorithm still works fine.
With this patch, the latency dropped to just 150us over a 20 hour run.
Without the patch, the huge latencies would trigger in seconds.
I've created a new sched feature called RT_PUSH_IPI, which is enabled
by default.
When RT_PUSH_IPI is not enabled, the old method of grabbing the rq locks
and having the pulling CPU do the work is implemented. When RT_PUSH_IPI
is enabled, the IPI is sent to the overloaded CPU to do a push.
To enabled or disable this at run time:
# mount -t debugfs nodev /sys/kernel/debug
# echo RT_PUSH_IPI > /sys/kernel/debug/sched_features
or
# echo NO_RT_PUSH_IPI > /sys/kernel/debug/sched_features
Update: This original patch would send an IPI to all CPUs in the RT overload
list. But that could theoretically cause the reverse issue. That is, there
could be lots of overloaded RT queues and one CPU lowers its priority. It would
then send an IPI to all the overloaded RT queues and they could then all try
to grab the rq lock of the CPU lowering its priority, and then we have the
same problem.
The latest design sends out only one IPI to the first overloaded CPU. It tries to
push any tasks that it can, and then looks for the next overloaded CPU that can
push to the source CPU. The IPIs stop when all overloaded CPUs that have pushable
tasks that have priorities greater than the source CPU are covered. In case the
source CPU lowers its priority again, a flag is set to tell the IPI traversal to
restart with the first RT overloaded CPU after the source CPU.
Parts-suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Joern Engel <joern@purestorage.com>
Cc: Clark Williams <williams@redhat.com>
Cc: Mike Galbraith <umgwanakikbuti@gmail.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20150318144946.2f3cc982@gandalf.local.home
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2015-03-18 18:49:46 +00:00
|
|
|
return;
|
2018-01-24 01:45:38 +00:00
|
|
|
}
|
sched/rt: Use IPI to trigger RT task push migration instead of pulling
When debugging the latencies on a 40 core box, where we hit 300 to
500 microsecond latencies, I found there was a huge contention on the
runqueue locks.
Investigating it further, running ftrace, I found that it was due to
the pulling of RT tasks.
The test that was run was the following:
cyclictest --numa -p95 -m -d0 -i100
This created a thread on each CPU, that would set its wakeup in iterations
of 100 microseconds. The -d0 means that all the threads had the same
interval (100us). Each thread sleeps for 100us and wakes up and measures
its latencies.
cyclictest is maintained at:
git://git.kernel.org/pub/scm/linux/kernel/git/clrkwllms/rt-tests.git
What happened was another RT task would be scheduled on one of the CPUs
that was running our test, when the other CPU tests went to sleep and
scheduled idle. This caused the "pull" operation to execute on all
these CPUs. Each one of these saw the RT task that was overloaded on
the CPU of the test that was still running, and each one tried
to grab that task in a thundering herd way.
To grab the task, each thread would do a double rq lock grab, grabbing
its own lock as well as the rq of the overloaded CPU. As the sched
domains on this box was rather flat for its size, I saw up to 12 CPUs
block on this lock at once. This caused a ripple affect with the
rq locks especially since the taking was done via a double rq lock, which
means that several of the CPUs had their own rq locks held while trying
to take this rq lock. As these locks were blocked, any wakeups or load
balanceing on these CPUs would also block on these locks, and the wait
time escalated.
I've tried various methods to lessen the load, but things like an
atomic counter to only let one CPU grab the task wont work, because
the task may have a limited affinity, and we may pick the wrong
CPU to take that lock and do the pull, to only find out that the
CPU we picked isn't in the task's affinity.
Instead of doing the PULL, I now have the CPUs that want the pull to
send over an IPI to the overloaded CPU, and let that CPU pick what
CPU to push the task to. No more need to grab the rq lock, and the
push/pull algorithm still works fine.
With this patch, the latency dropped to just 150us over a 20 hour run.
Without the patch, the huge latencies would trigger in seconds.
I've created a new sched feature called RT_PUSH_IPI, which is enabled
by default.
When RT_PUSH_IPI is not enabled, the old method of grabbing the rq locks
and having the pulling CPU do the work is implemented. When RT_PUSH_IPI
is enabled, the IPI is sent to the overloaded CPU to do a push.
To enabled or disable this at run time:
# mount -t debugfs nodev /sys/kernel/debug
# echo RT_PUSH_IPI > /sys/kernel/debug/sched_features
or
# echo NO_RT_PUSH_IPI > /sys/kernel/debug/sched_features
Update: This original patch would send an IPI to all CPUs in the RT overload
list. But that could theoretically cause the reverse issue. That is, there
could be lots of overloaded RT queues and one CPU lowers its priority. It would
then send an IPI to all the overloaded RT queues and they could then all try
to grab the rq lock of the CPU lowering its priority, and then we have the
same problem.
The latest design sends out only one IPI to the first overloaded CPU. It tries to
push any tasks that it can, and then looks for the next overloaded CPU that can
push to the source CPU. The IPIs stop when all overloaded CPUs that have pushable
tasks that have priorities greater than the source CPU are covered. In case the
source CPU lowers its priority again, a flag is set to tell the IPI traversal to
restart with the first RT overloaded CPU after the source CPU.
Parts-suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Joern Engel <joern@purestorage.com>
Cc: Clark Williams <williams@redhat.com>
Cc: Mike Galbraith <umgwanakikbuti@gmail.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20150318144946.2f3cc982@gandalf.local.home
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2015-03-18 18:49:46 +00:00
|
|
|
|
|
|
|
/* Try the next RT overloaded CPU */
|
2018-01-24 01:45:37 +00:00
|
|
|
irq_work_queue_on(&rd->rto_push_work, cpu);
|
sched/rt: Use IPI to trigger RT task push migration instead of pulling
When debugging the latencies on a 40 core box, where we hit 300 to
500 microsecond latencies, I found there was a huge contention on the
runqueue locks.
Investigating it further, running ftrace, I found that it was due to
the pulling of RT tasks.
The test that was run was the following:
cyclictest --numa -p95 -m -d0 -i100
This created a thread on each CPU, that would set its wakeup in iterations
of 100 microseconds. The -d0 means that all the threads had the same
interval (100us). Each thread sleeps for 100us and wakes up and measures
its latencies.
cyclictest is maintained at:
git://git.kernel.org/pub/scm/linux/kernel/git/clrkwllms/rt-tests.git
What happened was another RT task would be scheduled on one of the CPUs
that was running our test, when the other CPU tests went to sleep and
scheduled idle. This caused the "pull" operation to execute on all
these CPUs. Each one of these saw the RT task that was overloaded on
the CPU of the test that was still running, and each one tried
to grab that task in a thundering herd way.
To grab the task, each thread would do a double rq lock grab, grabbing
its own lock as well as the rq of the overloaded CPU. As the sched
domains on this box was rather flat for its size, I saw up to 12 CPUs
block on this lock at once. This caused a ripple affect with the
rq locks especially since the taking was done via a double rq lock, which
means that several of the CPUs had their own rq locks held while trying
to take this rq lock. As these locks were blocked, any wakeups or load
balanceing on these CPUs would also block on these locks, and the wait
time escalated.
I've tried various methods to lessen the load, but things like an
atomic counter to only let one CPU grab the task wont work, because
the task may have a limited affinity, and we may pick the wrong
CPU to take that lock and do the pull, to only find out that the
CPU we picked isn't in the task's affinity.
Instead of doing the PULL, I now have the CPUs that want the pull to
send over an IPI to the overloaded CPU, and let that CPU pick what
CPU to push the task to. No more need to grab the rq lock, and the
push/pull algorithm still works fine.
With this patch, the latency dropped to just 150us over a 20 hour run.
Without the patch, the huge latencies would trigger in seconds.
I've created a new sched feature called RT_PUSH_IPI, which is enabled
by default.
When RT_PUSH_IPI is not enabled, the old method of grabbing the rq locks
and having the pulling CPU do the work is implemented. When RT_PUSH_IPI
is enabled, the IPI is sent to the overloaded CPU to do a push.
To enabled or disable this at run time:
# mount -t debugfs nodev /sys/kernel/debug
# echo RT_PUSH_IPI > /sys/kernel/debug/sched_features
or
# echo NO_RT_PUSH_IPI > /sys/kernel/debug/sched_features
Update: This original patch would send an IPI to all CPUs in the RT overload
list. But that could theoretically cause the reverse issue. That is, there
could be lots of overloaded RT queues and one CPU lowers its priority. It would
then send an IPI to all the overloaded RT queues and they could then all try
to grab the rq lock of the CPU lowering its priority, and then we have the
same problem.
The latest design sends out only one IPI to the first overloaded CPU. It tries to
push any tasks that it can, and then looks for the next overloaded CPU that can
push to the source CPU. The IPIs stop when all overloaded CPUs that have pushable
tasks that have priorities greater than the source CPU are covered. In case the
source CPU lowers its priority again, a flag is set to tell the IPI traversal to
restart with the first RT overloaded CPU after the source CPU.
Parts-suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Joern Engel <joern@purestorage.com>
Cc: Clark Williams <williams@redhat.com>
Cc: Mike Galbraith <umgwanakikbuti@gmail.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20150318144946.2f3cc982@gandalf.local.home
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2015-03-18 18:49:46 +00:00
|
|
|
}
|
|
|
|
#endif /* HAVE_RT_PUSH_IPI */
|
|
|
|
|
2015-06-11 12:46:40 +00:00
|
|
|
static void pull_rt_task(struct rq *this_rq)
|
2008-01-25 20:08:07 +00:00
|
|
|
{
|
2015-06-11 12:46:40 +00:00
|
|
|
int this_cpu = this_rq->cpu, cpu;
|
|
|
|
bool resched = false;
|
2020-09-28 15:06:07 +00:00
|
|
|
struct task_struct *p, *push_task;
|
2008-01-25 20:08:07 +00:00
|
|
|
struct rq *src_rq;
|
sched/rt: Do not pull from current CPU if only one CPU to pull
Daniel Wagner reported a crash on the BeagleBone Black SoC.
This is a single CPU architecture, and does not have a functional
arch_send_call_function_single_ipi() implementation which can crash
the kernel if that is called.
As it only has one CPU, it shouldn't be called, but if the kernel is
compiled for SMP, the push/pull RT scheduling logic now calls it for
irq_work if the one CPU is overloaded, it can use that function to call
itself and crash the kernel.
Ideally, we should disable the SCHED_FEAT(RT_PUSH_IPI) if the system
only has a single CPU. But SCHED_FEAT is a constant if sched debugging
is turned off. Another fix can also be used, and this should also help
with normal SMP machines. That is, do not initiate the pull code if
there's only one RT overloaded CPU, and that CPU happens to be the
current CPU that is scheduling in a lower priority task.
Even on a system with many CPUs, if there's many RT tasks waiting to
run on a single CPU, and that CPU schedules in another RT task of lower
priority, it will initiate the PULL logic in case there's a higher
priority RT task on another CPU that is waiting to run. But if there is
no other CPU with waiting RT tasks, it will initiate the RT pull logic
on itself (as it still has RT tasks waiting to run). This is a wasted
effort.
Not only does this help with SMP code where the current CPU is the only
one with RT overloaded tasks, it should also solve the issue that
Daniel encountered, because it will prevent the PULL logic from
executing, as there's only one CPU on the system, and the check added
here will cause it to exit the RT pull code.
Reported-by: Daniel Wagner <wagi@monom.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-rt-users <linux-rt-users@vger.kernel.org>
Cc: stable@vger.kernel.org
Fixes: 4bdced5c9 ("sched/rt: Simplify the IPI based RT balancing logic")
Link: http://lkml.kernel.org/r/20171202130454.4cbbfe8d@vmware.local.home
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-12-02 18:04:54 +00:00
|
|
|
int rt_overload_count = rt_overloaded(this_rq);
|
2008-01-25 20:08:07 +00:00
|
|
|
|
sched/rt: Do not pull from current CPU if only one CPU to pull
Daniel Wagner reported a crash on the BeagleBone Black SoC.
This is a single CPU architecture, and does not have a functional
arch_send_call_function_single_ipi() implementation which can crash
the kernel if that is called.
As it only has one CPU, it shouldn't be called, but if the kernel is
compiled for SMP, the push/pull RT scheduling logic now calls it for
irq_work if the one CPU is overloaded, it can use that function to call
itself and crash the kernel.
Ideally, we should disable the SCHED_FEAT(RT_PUSH_IPI) if the system
only has a single CPU. But SCHED_FEAT is a constant if sched debugging
is turned off. Another fix can also be used, and this should also help
with normal SMP machines. That is, do not initiate the pull code if
there's only one RT overloaded CPU, and that CPU happens to be the
current CPU that is scheduling in a lower priority task.
Even on a system with many CPUs, if there's many RT tasks waiting to
run on a single CPU, and that CPU schedules in another RT task of lower
priority, it will initiate the PULL logic in case there's a higher
priority RT task on another CPU that is waiting to run. But if there is
no other CPU with waiting RT tasks, it will initiate the RT pull logic
on itself (as it still has RT tasks waiting to run). This is a wasted
effort.
Not only does this help with SMP code where the current CPU is the only
one with RT overloaded tasks, it should also solve the issue that
Daniel encountered, because it will prevent the PULL logic from
executing, as there's only one CPU on the system, and the check added
here will cause it to exit the RT pull code.
Reported-by: Daniel Wagner <wagi@monom.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-rt-users <linux-rt-users@vger.kernel.org>
Cc: stable@vger.kernel.org
Fixes: 4bdced5c9 ("sched/rt: Simplify the IPI based RT balancing logic")
Link: http://lkml.kernel.org/r/20171202130454.4cbbfe8d@vmware.local.home
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-12-02 18:04:54 +00:00
|
|
|
if (likely(!rt_overload_count))
|
2015-06-11 12:46:40 +00:00
|
|
|
return;
|
2008-01-25 20:08:07 +00:00
|
|
|
|
2013-10-15 10:35:07 +00:00
|
|
|
/*
|
|
|
|
* Match the barrier from rt_set_overloaded; this guarantees that if we
|
|
|
|
* see overloaded we must also see the rto_mask bit.
|
|
|
|
*/
|
|
|
|
smp_rmb();
|
|
|
|
|
sched/rt: Do not pull from current CPU if only one CPU to pull
Daniel Wagner reported a crash on the BeagleBone Black SoC.
This is a single CPU architecture, and does not have a functional
arch_send_call_function_single_ipi() implementation which can crash
the kernel if that is called.
As it only has one CPU, it shouldn't be called, but if the kernel is
compiled for SMP, the push/pull RT scheduling logic now calls it for
irq_work if the one CPU is overloaded, it can use that function to call
itself and crash the kernel.
Ideally, we should disable the SCHED_FEAT(RT_PUSH_IPI) if the system
only has a single CPU. But SCHED_FEAT is a constant if sched debugging
is turned off. Another fix can also be used, and this should also help
with normal SMP machines. That is, do not initiate the pull code if
there's only one RT overloaded CPU, and that CPU happens to be the
current CPU that is scheduling in a lower priority task.
Even on a system with many CPUs, if there's many RT tasks waiting to
run on a single CPU, and that CPU schedules in another RT task of lower
priority, it will initiate the PULL logic in case there's a higher
priority RT task on another CPU that is waiting to run. But if there is
no other CPU with waiting RT tasks, it will initiate the RT pull logic
on itself (as it still has RT tasks waiting to run). This is a wasted
effort.
Not only does this help with SMP code where the current CPU is the only
one with RT overloaded tasks, it should also solve the issue that
Daniel encountered, because it will prevent the PULL logic from
executing, as there's only one CPU on the system, and the check added
here will cause it to exit the RT pull code.
Reported-by: Daniel Wagner <wagi@monom.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-rt-users <linux-rt-users@vger.kernel.org>
Cc: stable@vger.kernel.org
Fixes: 4bdced5c9 ("sched/rt: Simplify the IPI based RT balancing logic")
Link: http://lkml.kernel.org/r/20171202130454.4cbbfe8d@vmware.local.home
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-12-02 18:04:54 +00:00
|
|
|
/* If we are the only overloaded CPU do nothing */
|
|
|
|
if (rt_overload_count == 1 &&
|
|
|
|
cpumask_test_cpu(this_rq->cpu, this_rq->rd->rto_mask))
|
|
|
|
return;
|
|
|
|
|
sched/rt: Use IPI to trigger RT task push migration instead of pulling
When debugging the latencies on a 40 core box, where we hit 300 to
500 microsecond latencies, I found there was a huge contention on the
runqueue locks.
Investigating it further, running ftrace, I found that it was due to
the pulling of RT tasks.
The test that was run was the following:
cyclictest --numa -p95 -m -d0 -i100
This created a thread on each CPU, that would set its wakeup in iterations
of 100 microseconds. The -d0 means that all the threads had the same
interval (100us). Each thread sleeps for 100us and wakes up and measures
its latencies.
cyclictest is maintained at:
git://git.kernel.org/pub/scm/linux/kernel/git/clrkwllms/rt-tests.git
What happened was another RT task would be scheduled on one of the CPUs
that was running our test, when the other CPU tests went to sleep and
scheduled idle. This caused the "pull" operation to execute on all
these CPUs. Each one of these saw the RT task that was overloaded on
the CPU of the test that was still running, and each one tried
to grab that task in a thundering herd way.
To grab the task, each thread would do a double rq lock grab, grabbing
its own lock as well as the rq of the overloaded CPU. As the sched
domains on this box was rather flat for its size, I saw up to 12 CPUs
block on this lock at once. This caused a ripple affect with the
rq locks especially since the taking was done via a double rq lock, which
means that several of the CPUs had their own rq locks held while trying
to take this rq lock. As these locks were blocked, any wakeups or load
balanceing on these CPUs would also block on these locks, and the wait
time escalated.
I've tried various methods to lessen the load, but things like an
atomic counter to only let one CPU grab the task wont work, because
the task may have a limited affinity, and we may pick the wrong
CPU to take that lock and do the pull, to only find out that the
CPU we picked isn't in the task's affinity.
Instead of doing the PULL, I now have the CPUs that want the pull to
send over an IPI to the overloaded CPU, and let that CPU pick what
CPU to push the task to. No more need to grab the rq lock, and the
push/pull algorithm still works fine.
With this patch, the latency dropped to just 150us over a 20 hour run.
Without the patch, the huge latencies would trigger in seconds.
I've created a new sched feature called RT_PUSH_IPI, which is enabled
by default.
When RT_PUSH_IPI is not enabled, the old method of grabbing the rq locks
and having the pulling CPU do the work is implemented. When RT_PUSH_IPI
is enabled, the IPI is sent to the overloaded CPU to do a push.
To enabled or disable this at run time:
# mount -t debugfs nodev /sys/kernel/debug
# echo RT_PUSH_IPI > /sys/kernel/debug/sched_features
or
# echo NO_RT_PUSH_IPI > /sys/kernel/debug/sched_features
Update: This original patch would send an IPI to all CPUs in the RT overload
list. But that could theoretically cause the reverse issue. That is, there
could be lots of overloaded RT queues and one CPU lowers its priority. It would
then send an IPI to all the overloaded RT queues and they could then all try
to grab the rq lock of the CPU lowering its priority, and then we have the
same problem.
The latest design sends out only one IPI to the first overloaded CPU. It tries to
push any tasks that it can, and then looks for the next overloaded CPU that can
push to the source CPU. The IPIs stop when all overloaded CPUs that have pushable
tasks that have priorities greater than the source CPU are covered. In case the
source CPU lowers its priority again, a flag is set to tell the IPI traversal to
restart with the first RT overloaded CPU after the source CPU.
Parts-suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Joern Engel <joern@purestorage.com>
Cc: Clark Williams <williams@redhat.com>
Cc: Mike Galbraith <umgwanakikbuti@gmail.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20150318144946.2f3cc982@gandalf.local.home
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2015-03-18 18:49:46 +00:00
|
|
|
#ifdef HAVE_RT_PUSH_IPI
|
|
|
|
if (sched_feat(RT_PUSH_IPI)) {
|
|
|
|
tell_cpu_to_push(this_rq);
|
2015-06-11 12:46:40 +00:00
|
|
|
return;
|
sched/rt: Use IPI to trigger RT task push migration instead of pulling
When debugging the latencies on a 40 core box, where we hit 300 to
500 microsecond latencies, I found there was a huge contention on the
runqueue locks.
Investigating it further, running ftrace, I found that it was due to
the pulling of RT tasks.
The test that was run was the following:
cyclictest --numa -p95 -m -d0 -i100
This created a thread on each CPU, that would set its wakeup in iterations
of 100 microseconds. The -d0 means that all the threads had the same
interval (100us). Each thread sleeps for 100us and wakes up and measures
its latencies.
cyclictest is maintained at:
git://git.kernel.org/pub/scm/linux/kernel/git/clrkwllms/rt-tests.git
What happened was another RT task would be scheduled on one of the CPUs
that was running our test, when the other CPU tests went to sleep and
scheduled idle. This caused the "pull" operation to execute on all
these CPUs. Each one of these saw the RT task that was overloaded on
the CPU of the test that was still running, and each one tried
to grab that task in a thundering herd way.
To grab the task, each thread would do a double rq lock grab, grabbing
its own lock as well as the rq of the overloaded CPU. As the sched
domains on this box was rather flat for its size, I saw up to 12 CPUs
block on this lock at once. This caused a ripple affect with the
rq locks especially since the taking was done via a double rq lock, which
means that several of the CPUs had their own rq locks held while trying
to take this rq lock. As these locks were blocked, any wakeups or load
balanceing on these CPUs would also block on these locks, and the wait
time escalated.
I've tried various methods to lessen the load, but things like an
atomic counter to only let one CPU grab the task wont work, because
the task may have a limited affinity, and we may pick the wrong
CPU to take that lock and do the pull, to only find out that the
CPU we picked isn't in the task's affinity.
Instead of doing the PULL, I now have the CPUs that want the pull to
send over an IPI to the overloaded CPU, and let that CPU pick what
CPU to push the task to. No more need to grab the rq lock, and the
push/pull algorithm still works fine.
With this patch, the latency dropped to just 150us over a 20 hour run.
Without the patch, the huge latencies would trigger in seconds.
I've created a new sched feature called RT_PUSH_IPI, which is enabled
by default.
When RT_PUSH_IPI is not enabled, the old method of grabbing the rq locks
and having the pulling CPU do the work is implemented. When RT_PUSH_IPI
is enabled, the IPI is sent to the overloaded CPU to do a push.
To enabled or disable this at run time:
# mount -t debugfs nodev /sys/kernel/debug
# echo RT_PUSH_IPI > /sys/kernel/debug/sched_features
or
# echo NO_RT_PUSH_IPI > /sys/kernel/debug/sched_features
Update: This original patch would send an IPI to all CPUs in the RT overload
list. But that could theoretically cause the reverse issue. That is, there
could be lots of overloaded RT queues and one CPU lowers its priority. It would
then send an IPI to all the overloaded RT queues and they could then all try
to grab the rq lock of the CPU lowering its priority, and then we have the
same problem.
The latest design sends out only one IPI to the first overloaded CPU. It tries to
push any tasks that it can, and then looks for the next overloaded CPU that can
push to the source CPU. The IPIs stop when all overloaded CPUs that have pushable
tasks that have priorities greater than the source CPU are covered. In case the
source CPU lowers its priority again, a flag is set to tell the IPI traversal to
restart with the first RT overloaded CPU after the source CPU.
Parts-suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Joern Engel <joern@purestorage.com>
Cc: Clark Williams <williams@redhat.com>
Cc: Mike Galbraith <umgwanakikbuti@gmail.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20150318144946.2f3cc982@gandalf.local.home
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2015-03-18 18:49:46 +00:00
|
|
|
}
|
|
|
|
#endif
|
|
|
|
|
2008-11-24 16:05:05 +00:00
|
|
|
for_each_cpu(cpu, this_rq->rd->rto_mask) {
|
2008-01-25 20:08:07 +00:00
|
|
|
if (this_cpu == cpu)
|
|
|
|
continue;
|
|
|
|
|
|
|
|
src_rq = cpu_rq(cpu);
|
2008-12-29 14:39:50 +00:00
|
|
|
|
|
|
|
/*
|
|
|
|
* Don't bother taking the src_rq->lock if the next highest
|
|
|
|
* task is known to be lower-priority than our current task.
|
|
|
|
* This may look racy, but if this value is about to go
|
|
|
|
* logically higher, the src_rq will push this task away.
|
|
|
|
* And if its going logically lower, we do not care
|
|
|
|
*/
|
|
|
|
if (src_rq->rt.highest_prio.next >=
|
|
|
|
this_rq->rt.highest_prio.curr)
|
|
|
|
continue;
|
|
|
|
|
2008-01-25 20:08:07 +00:00
|
|
|
/*
|
|
|
|
* We can potentially drop this_rq's lock in
|
|
|
|
* double_lock_balance, and another CPU could
|
2008-12-29 14:39:49 +00:00
|
|
|
* alter this_rq
|
2008-01-25 20:08:07 +00:00
|
|
|
*/
|
2020-09-28 15:06:07 +00:00
|
|
|
push_task = NULL;
|
2008-12-29 14:39:49 +00:00
|
|
|
double_lock_balance(this_rq, src_rq);
|
2008-01-25 20:08:07 +00:00
|
|
|
|
|
|
|
/*
|
2013-06-07 19:37:43 +00:00
|
|
|
* We can pull only a task, which is pushable
|
|
|
|
* on its rq, and no others.
|
2008-01-25 20:08:07 +00:00
|
|
|
*/
|
2013-06-07 19:37:43 +00:00
|
|
|
p = pick_highest_pushable_task(src_rq, this_cpu);
|
2008-01-25 20:08:07 +00:00
|
|
|
|
|
|
|
/*
|
|
|
|
* Do we have an RT task that preempts
|
|
|
|
* the to-be-scheduled task?
|
|
|
|
*/
|
2008-12-29 14:39:49 +00:00
|
|
|
if (p && (p->prio < this_rq->rt.highest_prio.curr)) {
|
2008-01-25 20:08:07 +00:00
|
|
|
WARN_ON(p == src_rq->curr);
|
2014-08-20 09:47:32 +00:00
|
|
|
WARN_ON(!task_on_rq_queued(p));
|
2008-01-25 20:08:07 +00:00
|
|
|
|
|
|
|
/*
|
|
|
|
* There's a chance that p is higher in priority
|
sched: Clean up and harmonize the coding style of the scheduler code base
A good number of small style inconsistencies have accumulated
in the scheduler core, so do a pass over them to harmonize
all these details:
- fix speling in comments,
- use curly braces for multi-line statements,
- remove unnecessary parentheses from integer literals,
- capitalize consistently,
- remove stray newlines,
- add comments where necessary,
- remove invalid/unnecessary comments,
- align structure definitions and other data types vertically,
- add missing newlines for increased readability,
- fix vertical tabulation where it's misaligned,
- harmonize preprocessor conditional block labeling
and vertical alignment,
- remove line-breaks where they uglify the code,
- add newline after local variable definitions,
No change in functionality:
md5:
1191fa0a890cfa8132156d2959d7e9e2 built-in.o.before.asm
1191fa0a890cfa8132156d2959d7e9e2 built-in.o.after.asm
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-03-03 13:01:12 +00:00
|
|
|
* than what's currently running on its CPU.
|
2021-03-18 12:38:50 +00:00
|
|
|
* This is just that p is waking up and hasn't
|
2008-01-25 20:08:07 +00:00
|
|
|
* had a chance to schedule. We only pull
|
|
|
|
* p if it is lower in priority than the
|
2008-12-29 14:39:49 +00:00
|
|
|
* current task on the run queue
|
2008-01-25 20:08:07 +00:00
|
|
|
*/
|
2008-12-29 14:39:49 +00:00
|
|
|
if (p->prio < src_rq->curr->prio)
|
2008-01-25 20:08:30 +00:00
|
|
|
goto skip;
|
2008-01-25 20:08:07 +00:00
|
|
|
|
2020-09-28 15:06:07 +00:00
|
|
|
if (is_migration_disabled(p)) {
|
|
|
|
push_task = get_push_task(src_rq);
|
|
|
|
} else {
|
|
|
|
deactivate_task(src_rq, p, 0);
|
|
|
|
set_task_cpu(p, this_cpu);
|
|
|
|
activate_task(this_rq, p, 0);
|
|
|
|
resched = true;
|
|
|
|
}
|
2008-01-25 20:08:07 +00:00
|
|
|
/*
|
|
|
|
* We continue with the search, just in
|
|
|
|
* case there's an even higher prio task
|
2011-03-31 01:57:33 +00:00
|
|
|
* in another runqueue. (low likelihood
|
2008-01-25 20:08:07 +00:00
|
|
|
* but possible)
|
|
|
|
*/
|
|
|
|
}
|
2010-10-17 19:46:10 +00:00
|
|
|
skip:
|
2008-08-11 07:30:22 +00:00
|
|
|
double_unlock_balance(this_rq, src_rq);
|
2020-09-28 15:06:07 +00:00
|
|
|
|
|
|
|
if (push_task) {
|
2020-11-17 23:19:31 +00:00
|
|
|
raw_spin_rq_unlock(this_rq);
|
2020-09-28 15:06:07 +00:00
|
|
|
stop_one_cpu_nowait(src_rq->cpu, push_cpu_stop,
|
|
|
|
push_task, &src_rq->push_work);
|
2020-11-17 23:19:31 +00:00
|
|
|
raw_spin_rq_lock(this_rq);
|
2020-09-28 15:06:07 +00:00
|
|
|
}
|
2008-01-25 20:08:07 +00:00
|
|
|
}
|
|
|
|
|
2015-06-11 12:46:40 +00:00
|
|
|
if (resched)
|
|
|
|
resched_curr(this_rq);
|
2008-01-25 20:08:07 +00:00
|
|
|
}
|
|
|
|
|
2008-04-23 11:13:29 +00:00
|
|
|
/*
|
|
|
|
* If we are not running and we are not going to reschedule soon, we should
|
|
|
|
* try to push tasks away now
|
|
|
|
*/
|
2009-12-16 17:04:40 +00:00
|
|
|
static void task_woken_rt(struct rq *rq, struct task_struct *p)
|
2008-01-25 20:08:07 +00:00
|
|
|
{
|
2022-09-06 10:33:04 +00:00
|
|
|
bool need_to_push = !task_on_cpu(rq, p) &&
|
2019-10-09 10:46:11 +00:00
|
|
|
!test_tsk_need_resched(rq->curr) &&
|
|
|
|
p->nr_cpus_allowed > 1 &&
|
|
|
|
(dl_task(rq->curr) || rt_task(rq->curr)) &&
|
|
|
|
(rq->curr->nr_cpus_allowed < 2 ||
|
|
|
|
rq->curr->prio <= p->prio);
|
|
|
|
|
2020-03-02 13:27:20 +00:00
|
|
|
if (need_to_push)
|
2008-01-25 20:08:07 +00:00
|
|
|
push_rt_tasks(rq);
|
|
|
|
}
|
|
|
|
|
2008-01-25 20:08:18 +00:00
|
|
|
/* Assumes rq->lock is held */
|
2008-06-04 19:04:05 +00:00
|
|
|
static void rq_online_rt(struct rq *rq)
|
2008-01-25 20:08:18 +00:00
|
|
|
{
|
|
|
|
if (rq->rt.overloaded)
|
|
|
|
rt_set_overload(rq);
|
2008-05-12 19:21:01 +00:00
|
|
|
|
2008-06-05 12:49:58 +00:00
|
|
|
__enable_runtime(rq);
|
|
|
|
|
2008-12-29 14:39:49 +00:00
|
|
|
cpupri_set(&rq->rd->cpupri, rq->cpu, rq->rt.highest_prio.curr);
|
2008-01-25 20:08:18 +00:00
|
|
|
}
|
|
|
|
|
|
|
|
/* Assumes rq->lock is held */
|
2008-06-04 19:04:05 +00:00
|
|
|
static void rq_offline_rt(struct rq *rq)
|
2008-01-25 20:08:18 +00:00
|
|
|
{
|
|
|
|
if (rq->rt.overloaded)
|
|
|
|
rt_clear_overload(rq);
|
2008-05-12 19:21:01 +00:00
|
|
|
|
2008-06-05 12:49:58 +00:00
|
|
|
__disable_runtime(rq);
|
|
|
|
|
2008-05-12 19:21:01 +00:00
|
|
|
cpupri_set(&rq->rd->cpupri, rq->cpu, CPUPRI_INVALID);
|
2008-01-25 20:08:18 +00:00
|
|
|
}
|
2008-01-25 20:08:22 +00:00
|
|
|
|
|
|
|
/*
|
|
|
|
* When switch from the rt queue, we bring ourselves to a position
|
|
|
|
* that we might want to pull RT tasks from other runqueues.
|
|
|
|
*/
|
2011-01-17 16:03:27 +00:00
|
|
|
static void switched_from_rt(struct rq *rq, struct task_struct *p)
|
2008-01-25 20:08:22 +00:00
|
|
|
{
|
|
|
|
/*
|
|
|
|
* If there are other RT tasks then we will reschedule
|
|
|
|
* and the scheduling of the other RT tasks will handle
|
|
|
|
* the balancing. But if we are the last RT task
|
|
|
|
* we may need to handle the pulling of RT tasks
|
|
|
|
* now.
|
|
|
|
*/
|
2014-08-20 09:47:32 +00:00
|
|
|
if (!task_on_rq_queued(p) || rq->rt.rt_nr_running)
|
2012-11-22 20:02:15 +00:00
|
|
|
return;
|
|
|
|
|
2018-03-03 15:27:54 +00:00
|
|
|
rt_queue_pull_task(rq);
|
2008-01-25 20:08:22 +00:00
|
|
|
}
|
2008-11-24 23:28:41 +00:00
|
|
|
|
2014-02-08 06:17:45 +00:00
|
|
|
void __init init_sched_rt_class(void)
|
2008-11-24 23:28:41 +00:00
|
|
|
{
|
|
|
|
unsigned int i;
|
|
|
|
|
2011-10-25 08:00:11 +00:00
|
|
|
for_each_possible_cpu(i) {
|
2009-06-06 21:51:36 +00:00
|
|
|
zalloc_cpumask_var_node(&per_cpu(local_cpu_mask, i),
|
2009-01-01 02:08:45 +00:00
|
|
|
GFP_KERNEL, cpu_to_node(i));
|
2011-10-25 08:00:11 +00:00
|
|
|
}
|
2008-11-24 23:28:41 +00:00
|
|
|
}
|
2008-01-25 20:08:22 +00:00
|
|
|
#endif /* CONFIG_SMP */
|
|
|
|
|
|
|
|
/*
|
|
|
|
* When switching a task to RT, we may overload the runqueue
|
|
|
|
* with RT tasks. In this case we try to push them off to
|
|
|
|
* other runqueues.
|
|
|
|
*/
|
2011-01-17 16:03:27 +00:00
|
|
|
static void switched_to_rt(struct rq *rq, struct task_struct *p)
|
2008-01-25 20:08:22 +00:00
|
|
|
{
|
|
|
|
/*
|
sched/rt: Fix RT utilization tracking during policy change
RT keeps track of the utilization on a per-rq basis with the structure
avg_rt. This utilization is updated during task_tick_rt(),
put_prev_task_rt() and set_next_task_rt(). However, when the current
running task changes its policy, set_next_task_rt() which would usually
take care of updating the utilization when the rq starts running RT tasks,
will not see a such change, leaving the avg_rt structure outdated. When
that very same task will be dequeued later, put_prev_task_rt() will then
update the utilization, based on a wrong last_update_time, leading to a
huge spike in the RT utilization signal.
The signal would eventually recover from this issue after few ms. Even if
no RT tasks are run, avg_rt is also updated in __update_blocked_others().
But as the CPU capacity depends partly on the avg_rt, this issue has
nonetheless a significant impact on the scheduler.
Fix this issue by ensuring a load update when a running task changes
its policy to RT.
Fixes: 371bf427 ("sched/rt: Add rt_rq utilization tracking")
Signed-off-by: Vincent Donnefort <vincent.donnefort@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Link: https://lore.kernel.org/r/1624271872-211872-2-git-send-email-vincent.donnefort@arm.com
2021-06-21 10:37:51 +00:00
|
|
|
* If we are running, update the avg_rt tracking, as the running time
|
|
|
|
* will now on be accounted into the latter.
|
|
|
|
*/
|
|
|
|
if (task_current(rq, p)) {
|
|
|
|
update_rt_rq_load_avg(rq_clock_pelt(rq), rq, 0);
|
|
|
|
return;
|
|
|
|
}
|
|
|
|
|
|
|
|
/*
|
|
|
|
* If we are not running we may need to preempt the current
|
|
|
|
* running task. If that current running task is also an RT task
|
2008-01-25 20:08:22 +00:00
|
|
|
* then see if we can move to another run queue.
|
|
|
|
*/
|
sched/rt: Fix RT utilization tracking during policy change
RT keeps track of the utilization on a per-rq basis with the structure
avg_rt. This utilization is updated during task_tick_rt(),
put_prev_task_rt() and set_next_task_rt(). However, when the current
running task changes its policy, set_next_task_rt() which would usually
take care of updating the utilization when the rq starts running RT tasks,
will not see a such change, leaving the avg_rt structure outdated. When
that very same task will be dequeued later, put_prev_task_rt() will then
update the utilization, based on a wrong last_update_time, leading to a
huge spike in the RT utilization signal.
The signal would eventually recover from this issue after few ms. Even if
no RT tasks are run, avg_rt is also updated in __update_blocked_others().
But as the CPU capacity depends partly on the avg_rt, this issue has
nonetheless a significant impact on the scheduler.
Fix this issue by ensuring a load update when a running task changes
its policy to RT.
Fixes: 371bf427 ("sched/rt: Add rt_rq utilization tracking")
Signed-off-by: Vincent Donnefort <vincent.donnefort@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Link: https://lore.kernel.org/r/1624271872-211872-2-git-send-email-vincent.donnefort@arm.com
2021-06-21 10:37:51 +00:00
|
|
|
if (task_on_rq_queued(p)) {
|
2008-01-25 20:08:22 +00:00
|
|
|
#ifdef CONFIG_SMP
|
2020-03-02 13:27:20 +00:00
|
|
|
if (p->nr_cpus_allowed > 1 && rq->rt.overloaded)
|
2018-03-03 15:27:54 +00:00
|
|
|
rt_queue_push_tasks(rq);
|
2017-01-24 14:40:06 +00:00
|
|
|
#endif /* CONFIG_SMP */
|
2017-10-14 00:00:18 +00:00
|
|
|
if (p->prio < rq->curr->prio && cpu_online(cpu_of(rq)))
|
2014-06-28 20:03:57 +00:00
|
|
|
resched_curr(rq);
|
2008-01-25 20:08:22 +00:00
|
|
|
}
|
|
|
|
}
|
|
|
|
|
|
|
|
/*
|
|
|
|
* Priority of the task has changed. This may cause
|
|
|
|
* us to initiate a push or pull.
|
|
|
|
*/
|
2011-01-17 16:03:27 +00:00
|
|
|
static void
|
|
|
|
prio_changed_rt(struct rq *rq, struct task_struct *p, int oldprio)
|
2008-01-25 20:08:22 +00:00
|
|
|
{
|
2014-08-20 09:47:32 +00:00
|
|
|
if (!task_on_rq_queued(p))
|
2011-01-17 16:03:27 +00:00
|
|
|
return;
|
|
|
|
|
2020-10-30 17:32:23 +00:00
|
|
|
if (task_current(rq, p)) {
|
2008-01-25 20:08:22 +00:00
|
|
|
#ifdef CONFIG_SMP
|
|
|
|
/*
|
|
|
|
* If our priority decreases while running, we
|
|
|
|
* may need to pull tasks to this runqueue.
|
|
|
|
*/
|
|
|
|
if (oldprio < p->prio)
|
2018-03-03 15:27:54 +00:00
|
|
|
rt_queue_pull_task(rq);
|
2015-06-11 12:46:41 +00:00
|
|
|
|
2008-01-25 20:08:22 +00:00
|
|
|
/*
|
|
|
|
* If there's a higher priority task waiting to run
|
2015-06-11 12:46:41 +00:00
|
|
|
* then reschedule.
|
2008-01-25 20:08:22 +00:00
|
|
|
*/
|
2015-06-11 12:46:41 +00:00
|
|
|
if (p->prio > rq->rt.highest_prio.curr)
|
2014-06-28 20:03:57 +00:00
|
|
|
resched_curr(rq);
|
2008-01-25 20:08:22 +00:00
|
|
|
#else
|
|
|
|
/* For UP simply resched on drop of prio */
|
|
|
|
if (oldprio < p->prio)
|
2014-06-28 20:03:57 +00:00
|
|
|
resched_curr(rq);
|
2008-01-25 20:08:05 +00:00
|
|
|
#endif /* CONFIG_SMP */
|
2008-01-25 20:08:22 +00:00
|
|
|
} else {
|
|
|
|
/*
|
|
|
|
* This task is not running, but if it is
|
|
|
|
* greater than the current running task
|
|
|
|
* then reschedule.
|
|
|
|
*/
|
|
|
|
if (p->prio < rq->curr->prio)
|
2014-06-28 20:03:57 +00:00
|
|
|
resched_curr(rq);
|
2008-01-25 20:08:22 +00:00
|
|
|
}
|
|
|
|
}
|
|
|
|
|
2017-01-21 05:09:08 +00:00
|
|
|
#ifdef CONFIG_POSIX_TIMERS
|
2008-01-25 20:08:27 +00:00
|
|
|
static void watchdog(struct rq *rq, struct task_struct *p)
|
|
|
|
{
|
|
|
|
unsigned long soft, hard;
|
|
|
|
|
2010-03-05 21:42:54 +00:00
|
|
|
/* max may change after cur was read, this will be fixed next tick */
|
|
|
|
soft = task_rlimit(p, RLIMIT_RTTIME);
|
|
|
|
hard = task_rlimit_max(p, RLIMIT_RTTIME);
|
2008-01-25 20:08:27 +00:00
|
|
|
|
|
|
|
if (soft != RLIM_INFINITY) {
|
|
|
|
unsigned long next;
|
|
|
|
|
sched/rt: Avoid updating RT entry timeout twice within one tick period
The issue below was found in 2.6.34-rt rather than mainline rt
kernel, but the issue still exists upstream as well.
So please let me describe how it was noticed on 2.6.34-rt:
On this version, each softirq has its own thread, it means there
is at least one RT FIFO task per cpu. The priority of these
tasks is set to 49 by default. If user launches an RT FIFO task
with priority lower than 49 of softirq RT tasks, it's possible
there are two RT FIFO tasks enqueued one cpu runqueue at one
moment. By current strategy of balancing RT tasks, when it comes
to RT tasks, we really need to put them off to a CPU that they
can run on as soon as possible. Even if it means a bit of cache
line flushing, we want RT tasks to be run with the least latency.
When the user RT FIFO task which just launched before is
running, the sched timer tick of the current cpu happens. In this
tick period, the timeout value of the user RT task will be
updated once. Subsequently, we try to wake up one softirq RT
task on its local cpu. As the priority of current user RT task
is lower than the softirq RT task, the current task will be
preempted by the higher priority softirq RT task. Before
preemption, we check to see if current can readily move to a
different cpu. If so, we will reschedule to allow the RT push logic
to try to move current somewhere else. Whenever the woken
softirq RT task runs, it first tries to migrate the user FIFO RT
task over to a cpu that is running a task of lesser priority. If
migration is done, it will send a reschedule request to the found
cpu by IPI interrupt. Once the target cpu responds the IPI
interrupt, it will pick the migrated user RT task to preempt its
current task. When the user RT task is running on the new cpu,
the sched timer tick of the cpu fires. So it will tick the user
RT task again. This also means the RT task timeout value will be
updated again. As the migration may be done in one tick period,
it means the user RT task timeout value will be updated twice
within one tick.
If we set a limit on the amount of cpu time for the user RT task
by setrlimit(RLIMIT_RTTIME), the SIGXCPU signal should be posted
upon reaching the soft limit.
But exactly when the SIGXCPU signal should be sent depends on the
RT task timeout value. In fact the timeout mechanism of sending
the SIGXCPU signal assumes the RT task timeout is increased once
every tick.
However, currently the timeout value may be added twice per
tick. So it results in the SIGXCPU signal being sent earlier
than expected.
To solve this issue, we prevent the timeout value from increasing
twice within one tick time by remembering the jiffies value of
last updating the timeout. As long as the RT task's jiffies is
different with the global jiffies value, we allow its timeout to
be updated.
Signed-off-by: Ying Xue <ying.xue@windriver.com>
Signed-off-by: Fan Du <fan.du@windriver.com>
Reviewed-by: Yong Zhang <yong.zhang0@gmail.com>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
Cc: <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1342508623-2887-1-git-send-email-ying.xue@windriver.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2012-07-17 07:03:43 +00:00
|
|
|
if (p->rt.watchdog_stamp != jiffies) {
|
|
|
|
p->rt.timeout++;
|
|
|
|
p->rt.watchdog_stamp = jiffies;
|
|
|
|
}
|
|
|
|
|
2008-01-25 20:08:27 +00:00
|
|
|
next = DIV_ROUND_UP(min(soft, hard), USEC_PER_SEC/HZ);
|
2019-08-21 19:09:06 +00:00
|
|
|
if (p->rt.timeout > next) {
|
|
|
|
posix_cputimers_rt_watchdog(&p->posix_cputimers,
|
|
|
|
p->se.sum_exec_runtime);
|
|
|
|
}
|
2008-01-25 20:08:27 +00:00
|
|
|
}
|
|
|
|
}
|
2017-01-21 05:09:08 +00:00
|
|
|
#else
|
|
|
|
static inline void watchdog(struct rq *rq, struct task_struct *p) { }
|
|
|
|
#endif
|
2007-07-09 16:51:58 +00:00
|
|
|
|
2018-02-21 04:17:27 +00:00
|
|
|
/*
|
|
|
|
* scheduler tick hitting a task of our scheduling class.
|
|
|
|
*
|
|
|
|
* NOTE: This function can be called remotely by the tick offload that
|
|
|
|
* goes along full dynticks. Therefore no local assumption can be made
|
|
|
|
* and everything must be accessed through the @rq and @curr passed in
|
|
|
|
* parameters.
|
|
|
|
*/
|
2008-01-25 20:08:29 +00:00
|
|
|
static void task_tick_rt(struct rq *rq, struct task_struct *p, int queued)
|
2007-07-09 16:51:58 +00:00
|
|
|
{
|
2012-05-17 04:34:23 +00:00
|
|
|
struct sched_rt_entity *rt_se = &p->rt;
|
|
|
|
|
2007-12-20 14:01:17 +00:00
|
|
|
update_curr_rt(rq);
|
sched/fair: Update scale invariance of PELT
The current implementation of load tracking invariance scales the
contribution with current frequency and uarch performance (only for
utilization) of the CPU. One main result of this formula is that the
figures are capped by current capacity of CPU. Another one is that the
load_avg is not invariant because not scaled with uarch.
The util_avg of a periodic task that runs r time slots every p time slots
varies in the range :
U * (1-y^r)/(1-y^p) * y^i < Utilization < U * (1-y^r)/(1-y^p)
with U is the max util_avg value = SCHED_CAPACITY_SCALE
At a lower capacity, the range becomes:
U * C * (1-y^r')/(1-y^p) * y^i' < Utilization < U * C * (1-y^r')/(1-y^p)
with C reflecting the compute capacity ratio between current capacity and
max capacity.
so C tries to compensate changes in (1-y^r') but it can't be accurate.
Instead of scaling the contribution value of PELT algo, we should scale the
running time. The PELT signal aims to track the amount of computation of
tasks and/or rq so it seems more correct to scale the running time to
reflect the effective amount of computation done since the last update.
In order to be fully invariant, we need to apply the same amount of
running time and idle time whatever the current capacity. Because running
at lower capacity implies that the task will run longer, we have to ensure
that the same amount of idle time will be applied when system becomes idle
and no idle time has been "stolen". But reaching the maximum utilization
value (SCHED_CAPACITY_SCALE) means that the task is seen as an
always-running task whatever the capacity of the CPU (even at max compute
capacity). In this case, we can discard this "stolen" idle times which
becomes meaningless.
In order to achieve this time scaling, a new clock_pelt is created per rq.
The increase of this clock scales with current capacity when something
is running on rq and synchronizes with clock_task when rq is idle. With
this mechanism, we ensure the same running and idle time whatever the
current capacity. This also enables to simplify the pelt algorithm by
removing all references of uarch and frequency and applying the same
contribution to utilization and loads. Furthermore, the scaling is done
only once per update of clock (update_rq_clock_task()) instead of during
each update of sched_entities and cfs/rt/dl_rq of the rq like the current
implementation. This is interesting when cgroup are involved as shown in
the results below:
On a hikey (octo Arm64 platform).
Performance cpufreq governor and only shallowest c-state to remove variance
generated by those power features so we only track the impact of pelt algo.
each test runs 16 times:
./perf bench sched pipe
(higher is better)
kernel tip/sched/core + patch
ops/seconds ops/seconds diff
cgroup
root 59652(+/- 0.18%) 59876(+/- 0.24%) +0.38%
level1 55608(+/- 0.27%) 55923(+/- 0.24%) +0.57%
level2 52115(+/- 0.29%) 52564(+/- 0.22%) +0.86%
hackbench -l 1000
(lower is better)
kernel tip/sched/core + patch
duration(sec) duration(sec) diff
cgroup
root 4.453(+/- 2.37%) 4.383(+/- 2.88%) -1.57%
level1 4.859(+/- 8.50%) 4.830(+/- 7.07%) -0.60%
level2 5.063(+/- 9.83%) 4.928(+/- 9.66%) -2.66%
Then, the responsiveness of PELT is improved when CPU is not running at max
capacity with this new algorithm. I have put below some examples of
duration to reach some typical load values according to the capacity of the
CPU with current implementation and with this patch. These values has been
computed based on the geometric series and the half period value:
Util (%) max capacity half capacity(mainline) half capacity(w/ patch)
972 (95%) 138ms not reachable 276ms
486 (47.5%) 30ms 138ms 60ms
256 (25%) 13ms 32ms 26ms
On my hikey (octo Arm64 platform) with schedutil governor, the time to
reach max OPP when starting from a null utilization, decreases from 223ms
with current scale invariance down to 121ms with the new algorithm.
Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Morten.Rasmussen@arm.com
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: bsegall@google.com
Cc: dietmar.eggemann@arm.com
Cc: patrick.bellasi@arm.com
Cc: pjt@google.com
Cc: pkondeti@codeaurora.org
Cc: quentin.perret@arm.com
Cc: rjw@rjwysocki.net
Cc: srinivas.pandruvada@linux.intel.com
Cc: thara.gopinath@linaro.org
Link: https://lkml.kernel.org/r/1548257214-13745-3-git-send-email-vincent.guittot@linaro.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2019-01-23 15:26:53 +00:00
|
|
|
update_rt_rq_load_avg(rq_clock_pelt(rq), rq, 1);
|
2007-12-20 14:01:17 +00:00
|
|
|
|
2008-01-25 20:08:27 +00:00
|
|
|
watchdog(rq, p);
|
|
|
|
|
2007-07-09 16:51:58 +00:00
|
|
|
/*
|
|
|
|
* RR tasks need a special form of timeslice management.
|
|
|
|
* FIFO tasks have no timeslices.
|
|
|
|
*/
|
|
|
|
if (p->policy != SCHED_RR)
|
|
|
|
return;
|
|
|
|
|
2008-01-25 20:08:27 +00:00
|
|
|
if (--p->rt.time_slice)
|
2007-07-09 16:51:58 +00:00
|
|
|
return;
|
|
|
|
|
2013-02-07 15:47:04 +00:00
|
|
|
p->rt.time_slice = sched_rr_timeslice;
|
2007-07-09 16:51:58 +00:00
|
|
|
|
2007-08-24 18:39:10 +00:00
|
|
|
/*
|
2013-10-21 12:15:43 +00:00
|
|
|
* Requeue to the end of queue if we (and all of our ancestors) are not
|
|
|
|
* the only element on the queue
|
2007-08-24 18:39:10 +00:00
|
|
|
*/
|
2012-05-17 04:34:23 +00:00
|
|
|
for_each_sched_rt_entity(rt_se) {
|
|
|
|
if (rt_se->run_list.prev != rt_se->run_list.next) {
|
|
|
|
requeue_task_rt(rq, p, 0);
|
2014-09-22 18:36:43 +00:00
|
|
|
resched_curr(rq);
|
2012-05-17 04:34:23 +00:00
|
|
|
return;
|
|
|
|
}
|
2007-08-24 18:39:10 +00:00
|
|
|
}
|
2007-07-09 16:51:58 +00:00
|
|
|
}
|
|
|
|
|
2010-01-14 03:21:52 +00:00
|
|
|
static unsigned int get_rr_interval_rt(struct rq *rq, struct task_struct *task)
|
2009-09-21 01:31:53 +00:00
|
|
|
{
|
|
|
|
/*
|
|
|
|
* Time slice is 0 for SCHED_FIFO tasks
|
|
|
|
*/
|
|
|
|
if (task->policy == SCHED_RR)
|
2013-02-07 15:47:04 +00:00
|
|
|
return sched_rr_timeslice;
|
2009-09-21 01:31:53 +00:00
|
|
|
else
|
|
|
|
return 0;
|
|
|
|
}
|
|
|
|
|
2020-10-21 13:45:33 +00:00
|
|
|
DEFINE_SCHED_CLASS(rt) = {
|
|
|
|
|
2007-07-09 16:51:58 +00:00
|
|
|
.enqueue_task = enqueue_task_rt,
|
|
|
|
.dequeue_task = dequeue_task_rt,
|
|
|
|
.yield_task = yield_task_rt,
|
|
|
|
|
|
|
|
.check_preempt_curr = check_preempt_curr_rt,
|
|
|
|
|
|
|
|
.pick_next_task = pick_next_task_rt,
|
|
|
|
.put_prev_task = put_prev_task_rt,
|
2019-05-29 20:36:41 +00:00
|
|
|
.set_next_task = set_next_task_rt,
|
2007-07-09 16:51:58 +00:00
|
|
|
|
2007-10-24 16:23:51 +00:00
|
|
|
#ifdef CONFIG_SMP
|
2019-11-08 10:11:52 +00:00
|
|
|
.balance = balance_rt,
|
2020-11-17 23:19:32 +00:00
|
|
|
.pick_task = pick_task_rt,
|
2008-10-22 07:25:26 +00:00
|
|
|
.select_task_rq = select_task_rq_rt,
|
2015-05-15 15:43:36 +00:00
|
|
|
.set_cpus_allowed = set_cpus_allowed_common,
|
2008-06-04 19:04:05 +00:00
|
|
|
.rq_online = rq_online_rt,
|
|
|
|
.rq_offline = rq_offline_rt,
|
2009-12-16 17:04:40 +00:00
|
|
|
.task_woken = task_woken_rt,
|
2008-01-25 20:08:22 +00:00
|
|
|
.switched_from = switched_from_rt,
|
2020-09-28 15:06:07 +00:00
|
|
|
.find_lock_rq = find_lock_lowest_rq,
|
2007-10-24 16:23:51 +00:00
|
|
|
#endif
|
2007-07-09 16:51:58 +00:00
|
|
|
|
|
|
|
.task_tick = task_tick_rt,
|
2008-01-25 20:08:22 +00:00
|
|
|
|
2009-09-21 01:31:53 +00:00
|
|
|
.get_rr_interval = get_rr_interval_rt,
|
|
|
|
|
2008-01-25 20:08:22 +00:00
|
|
|
.prio_changed = prio_changed_rt,
|
|
|
|
.switched_to = switched_to_rt,
|
sched/cputime: Fix clock_nanosleep()/clock_gettime() inconsistency
Commit d670ec13178d0 "posix-cpu-timers: Cure SMP wobbles" fixes one glibc
test case in cost of breaking another one. After that commit, calling
clock_nanosleep(TIMER_ABSTIME, X) and then clock_gettime(&Y) can result
of Y time being smaller than X time.
Reproducer/tester can be found further below, it can be compiled and ran by:
gcc -o tst-cpuclock2 tst-cpuclock2.c -pthread
while ./tst-cpuclock2 ; do : ; done
This reproducer, when running on a buggy kernel, will complain
about "clock_gettime difference too small".
Issue happens because on start in thread_group_cputimer() we initialize
sum_exec_runtime of cputimer with threads runtime not yet accounted and
then add the threads runtime to running cputimer again on scheduler
tick, making it's sum_exec_runtime bigger than actual threads runtime.
KOSAKI Motohiro posted a fix for this problem, but that patch was never
applied: https://lkml.org/lkml/2013/5/26/191 .
This patch takes different approach to cure the problem. It calls
update_curr() when cputimer starts, that assure we will have updated
stats of running threads and on the next schedule tick we will account
only the runtime that elapsed from cputimer start. That also assure we
have consistent state between cpu times of individual threads and cpu
time of the process consisted by those threads.
Full reproducer (tst-cpuclock2.c):
#define _GNU_SOURCE
#include <unistd.h>
#include <sys/syscall.h>
#include <stdio.h>
#include <time.h>
#include <pthread.h>
#include <stdint.h>
#include <inttypes.h>
/* Parameters for the Linux kernel ABI for CPU clocks. */
#define CPUCLOCK_SCHED 2
#define MAKE_PROCESS_CPUCLOCK(pid, clock) \
((~(clockid_t) (pid) << 3) | (clockid_t) (clock))
static pthread_barrier_t barrier;
/* Help advance the clock. */
static void *chew_cpu(void *arg)
{
pthread_barrier_wait(&barrier);
while (1) ;
return NULL;
}
/* Don't use the glibc wrapper. */
static int do_nanosleep(int flags, const struct timespec *req)
{
clockid_t clock_id = MAKE_PROCESS_CPUCLOCK(0, CPUCLOCK_SCHED);
return syscall(SYS_clock_nanosleep, clock_id, flags, req, NULL);
}
static int64_t tsdiff(const struct timespec *before, const struct timespec *after)
{
int64_t before_i = before->tv_sec * 1000000000ULL + before->tv_nsec;
int64_t after_i = after->tv_sec * 1000000000ULL + after->tv_nsec;
return after_i - before_i;
}
int main(void)
{
int result = 0;
pthread_t th;
pthread_barrier_init(&barrier, NULL, 2);
if (pthread_create(&th, NULL, chew_cpu, NULL) != 0) {
perror("pthread_create");
return 1;
}
pthread_barrier_wait(&barrier);
/* The test. */
struct timespec before, after, sleeptimeabs;
int64_t sleepdiff, diffabs;
const struct timespec sleeptime = {.tv_sec = 0,.tv_nsec = 100000000 };
/* The relative nanosleep. Not sure why this is needed, but its presence
seems to make it easier to reproduce the problem. */
if (do_nanosleep(0, &sleeptime) != 0) {
perror("clock_nanosleep");
return 1;
}
/* Get the current time. */
if (clock_gettime(CLOCK_PROCESS_CPUTIME_ID, &before) < 0) {
perror("clock_gettime[2]");
return 1;
}
/* Compute the absolute sleep time based on the current time. */
uint64_t nsec = before.tv_nsec + sleeptime.tv_nsec;
sleeptimeabs.tv_sec = before.tv_sec + nsec / 1000000000;
sleeptimeabs.tv_nsec = nsec % 1000000000;
/* Sleep for the computed time. */
if (do_nanosleep(TIMER_ABSTIME, &sleeptimeabs) != 0) {
perror("absolute clock_nanosleep");
return 1;
}
/* Get the time after the sleep. */
if (clock_gettime(CLOCK_PROCESS_CPUTIME_ID, &after) < 0) {
perror("clock_gettime[3]");
return 1;
}
/* The time after sleep should always be equal to or after the absolute sleep
time passed to clock_nanosleep. */
sleepdiff = tsdiff(&sleeptimeabs, &after);
if (sleepdiff < 0) {
printf("absolute clock_nanosleep woke too early: %" PRId64 "\n", sleepdiff);
result = 1;
printf("Before %llu.%09llu\n", before.tv_sec, before.tv_nsec);
printf("After %llu.%09llu\n", after.tv_sec, after.tv_nsec);
printf("Sleep %llu.%09llu\n", sleeptimeabs.tv_sec, sleeptimeabs.tv_nsec);
}
/* The difference between the timestamps taken before and after the
clock_nanosleep call should be equal to or more than the duration of the
sleep. */
diffabs = tsdiff(&before, &after);
if (diffabs < sleeptime.tv_nsec) {
printf("clock_gettime difference too small: %" PRId64 "\n", diffabs);
result = 1;
}
pthread_cancel(th);
return result;
}
Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/20141112155843.GA24803@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2014-11-12 15:58:44 +00:00
|
|
|
|
|
|
|
.update_curr = update_curr_rt,
|
2019-06-21 08:42:10 +00:00
|
|
|
|
|
|
|
#ifdef CONFIG_UCLAMP_TASK
|
|
|
|
.uclamp_enabled = 1,
|
|
|
|
#endif
|
2007-07-09 16:51:58 +00:00
|
|
|
};
|
2008-06-19 12:22:24 +00:00
|
|
|
|
2017-06-21 18:22:02 +00:00
|
|
|
#ifdef CONFIG_RT_GROUP_SCHED
|
|
|
|
/*
|
|
|
|
* Ensure that the real time constraints are schedulable.
|
|
|
|
*/
|
|
|
|
static DEFINE_MUTEX(rt_constraints_mutex);
|
|
|
|
|
|
|
|
static inline int tg_has_rt_tasks(struct task_group *tg)
|
|
|
|
{
|
2020-01-25 14:50:38 +00:00
|
|
|
struct task_struct *task;
|
|
|
|
struct css_task_iter it;
|
|
|
|
int ret = 0;
|
2017-06-21 18:22:02 +00:00
|
|
|
|
|
|
|
/*
|
|
|
|
* Autogroups do not have RT tasks; see autogroup_create().
|
|
|
|
*/
|
|
|
|
if (task_group_is_autogroup(tg))
|
|
|
|
return 0;
|
|
|
|
|
2020-01-25 14:50:38 +00:00
|
|
|
css_task_iter_start(&tg->css, 0, &it);
|
|
|
|
while (!ret && (task = css_task_iter_next(&it)))
|
|
|
|
ret |= rt_task(task);
|
|
|
|
css_task_iter_end(&it);
|
2017-06-21 18:22:02 +00:00
|
|
|
|
2020-01-25 14:50:38 +00:00
|
|
|
return ret;
|
2017-06-21 18:22:02 +00:00
|
|
|
}
|
|
|
|
|
|
|
|
struct rt_schedulable_data {
|
|
|
|
struct task_group *tg;
|
|
|
|
u64 rt_period;
|
|
|
|
u64 rt_runtime;
|
|
|
|
};
|
|
|
|
|
|
|
|
static int tg_rt_schedulable(struct task_group *tg, void *data)
|
|
|
|
{
|
|
|
|
struct rt_schedulable_data *d = data;
|
|
|
|
struct task_group *child;
|
|
|
|
unsigned long total, sum = 0;
|
|
|
|
u64 period, runtime;
|
|
|
|
|
|
|
|
period = ktime_to_ns(tg->rt_bandwidth.rt_period);
|
|
|
|
runtime = tg->rt_bandwidth.rt_runtime;
|
|
|
|
|
|
|
|
if (tg == d->tg) {
|
|
|
|
period = d->rt_period;
|
|
|
|
runtime = d->rt_runtime;
|
|
|
|
}
|
|
|
|
|
|
|
|
/*
|
|
|
|
* Cannot have more runtime than the period.
|
|
|
|
*/
|
|
|
|
if (runtime > period && runtime != RUNTIME_INF)
|
|
|
|
return -EINVAL;
|
|
|
|
|
|
|
|
/*
|
2020-01-25 14:50:38 +00:00
|
|
|
* Ensure we don't starve existing RT tasks if runtime turns zero.
|
2017-06-21 18:22:02 +00:00
|
|
|
*/
|
2020-01-25 14:50:38 +00:00
|
|
|
if (rt_bandwidth_enabled() && !runtime &&
|
|
|
|
tg->rt_bandwidth.rt_runtime && tg_has_rt_tasks(tg))
|
2017-06-21 18:22:02 +00:00
|
|
|
return -EBUSY;
|
|
|
|
|
|
|
|
total = to_ratio(period, runtime);
|
|
|
|
|
|
|
|
/*
|
|
|
|
* Nobody can have more than the global setting allows.
|
|
|
|
*/
|
|
|
|
if (total > to_ratio(global_rt_period(), global_rt_runtime()))
|
|
|
|
return -EINVAL;
|
|
|
|
|
|
|
|
/*
|
|
|
|
* The sum of our children's runtime should not exceed our own.
|
|
|
|
*/
|
|
|
|
list_for_each_entry_rcu(child, &tg->children, siblings) {
|
|
|
|
period = ktime_to_ns(child->rt_bandwidth.rt_period);
|
|
|
|
runtime = child->rt_bandwidth.rt_runtime;
|
|
|
|
|
|
|
|
if (child == d->tg) {
|
|
|
|
period = d->rt_period;
|
|
|
|
runtime = d->rt_runtime;
|
|
|
|
}
|
|
|
|
|
|
|
|
sum += to_ratio(period, runtime);
|
|
|
|
}
|
|
|
|
|
|
|
|
if (sum > total)
|
|
|
|
return -EINVAL;
|
|
|
|
|
|
|
|
return 0;
|
|
|
|
}
|
|
|
|
|
|
|
|
static int __rt_schedulable(struct task_group *tg, u64 period, u64 runtime)
|
|
|
|
{
|
|
|
|
int ret;
|
|
|
|
|
|
|
|
struct rt_schedulable_data data = {
|
|
|
|
.tg = tg,
|
|
|
|
.rt_period = period,
|
|
|
|
.rt_runtime = runtime,
|
|
|
|
};
|
|
|
|
|
|
|
|
rcu_read_lock();
|
|
|
|
ret = walk_tg_tree(tg_rt_schedulable, tg_nop, &data);
|
|
|
|
rcu_read_unlock();
|
|
|
|
|
|
|
|
return ret;
|
|
|
|
}
|
|
|
|
|
|
|
|
static int tg_set_rt_bandwidth(struct task_group *tg,
|
|
|
|
u64 rt_period, u64 rt_runtime)
|
|
|
|
{
|
|
|
|
int i, err = 0;
|
|
|
|
|
|
|
|
/*
|
|
|
|
* Disallowing the root group RT runtime is BAD, it would disallow the
|
|
|
|
* kernel creating (and or operating) RT threads.
|
|
|
|
*/
|
|
|
|
if (tg == &root_task_group && rt_runtime == 0)
|
|
|
|
return -EINVAL;
|
|
|
|
|
|
|
|
/* No period doesn't make any sense. */
|
|
|
|
if (rt_period == 0)
|
|
|
|
return -EINVAL;
|
|
|
|
|
2020-04-25 10:52:48 +00:00
|
|
|
/*
|
|
|
|
* Bound quota to defend quota against overflow during bandwidth shift.
|
|
|
|
*/
|
|
|
|
if (rt_runtime != RUNTIME_INF && rt_runtime > max_rt_runtime)
|
|
|
|
return -EINVAL;
|
|
|
|
|
2017-06-21 18:22:02 +00:00
|
|
|
mutex_lock(&rt_constraints_mutex);
|
|
|
|
err = __rt_schedulable(tg, rt_period, rt_runtime);
|
|
|
|
if (err)
|
|
|
|
goto unlock;
|
|
|
|
|
|
|
|
raw_spin_lock_irq(&tg->rt_bandwidth.rt_runtime_lock);
|
|
|
|
tg->rt_bandwidth.rt_period = ns_to_ktime(rt_period);
|
|
|
|
tg->rt_bandwidth.rt_runtime = rt_runtime;
|
|
|
|
|
|
|
|
for_each_possible_cpu(i) {
|
|
|
|
struct rt_rq *rt_rq = tg->rt_rq[i];
|
|
|
|
|
|
|
|
raw_spin_lock(&rt_rq->rt_runtime_lock);
|
|
|
|
rt_rq->rt_runtime = rt_runtime;
|
|
|
|
raw_spin_unlock(&rt_rq->rt_runtime_lock);
|
|
|
|
}
|
|
|
|
raw_spin_unlock_irq(&tg->rt_bandwidth.rt_runtime_lock);
|
|
|
|
unlock:
|
|
|
|
mutex_unlock(&rt_constraints_mutex);
|
|
|
|
|
|
|
|
return err;
|
|
|
|
}
|
|
|
|
|
|
|
|
int sched_group_set_rt_runtime(struct task_group *tg, long rt_runtime_us)
|
|
|
|
{
|
|
|
|
u64 rt_runtime, rt_period;
|
|
|
|
|
|
|
|
rt_period = ktime_to_ns(tg->rt_bandwidth.rt_period);
|
|
|
|
rt_runtime = (u64)rt_runtime_us * NSEC_PER_USEC;
|
|
|
|
if (rt_runtime_us < 0)
|
|
|
|
rt_runtime = RUNTIME_INF;
|
2019-02-27 08:10:17 +00:00
|
|
|
else if ((u64)rt_runtime_us > U64_MAX / NSEC_PER_USEC)
|
|
|
|
return -EINVAL;
|
2017-06-21 18:22:02 +00:00
|
|
|
|
|
|
|
return tg_set_rt_bandwidth(tg, rt_period, rt_runtime);
|
|
|
|
}
|
|
|
|
|
|
|
|
long sched_group_rt_runtime(struct task_group *tg)
|
|
|
|
{
|
|
|
|
u64 rt_runtime_us;
|
|
|
|
|
|
|
|
if (tg->rt_bandwidth.rt_runtime == RUNTIME_INF)
|
|
|
|
return -1;
|
|
|
|
|
|
|
|
rt_runtime_us = tg->rt_bandwidth.rt_runtime;
|
|
|
|
do_div(rt_runtime_us, NSEC_PER_USEC);
|
|
|
|
return rt_runtime_us;
|
|
|
|
}
|
|
|
|
|
|
|
|
int sched_group_set_rt_period(struct task_group *tg, u64 rt_period_us)
|
|
|
|
{
|
|
|
|
u64 rt_runtime, rt_period;
|
|
|
|
|
2019-02-27 08:10:17 +00:00
|
|
|
if (rt_period_us > U64_MAX / NSEC_PER_USEC)
|
|
|
|
return -EINVAL;
|
|
|
|
|
2017-06-21 18:22:02 +00:00
|
|
|
rt_period = rt_period_us * NSEC_PER_USEC;
|
|
|
|
rt_runtime = tg->rt_bandwidth.rt_runtime;
|
|
|
|
|
|
|
|
return tg_set_rt_bandwidth(tg, rt_period, rt_runtime);
|
|
|
|
}
|
|
|
|
|
|
|
|
long sched_group_rt_period(struct task_group *tg)
|
|
|
|
{
|
|
|
|
u64 rt_period_us;
|
|
|
|
|
|
|
|
rt_period_us = ktime_to_ns(tg->rt_bandwidth.rt_period);
|
|
|
|
do_div(rt_period_us, NSEC_PER_USEC);
|
|
|
|
return rt_period_us;
|
|
|
|
}
|
|
|
|
|
2022-03-18 02:54:17 +00:00
|
|
|
#ifdef CONFIG_SYSCTL
|
2017-06-21 18:22:02 +00:00
|
|
|
static int sched_rt_global_constraints(void)
|
|
|
|
{
|
|
|
|
int ret = 0;
|
|
|
|
|
|
|
|
mutex_lock(&rt_constraints_mutex);
|
|
|
|
ret = __rt_schedulable(NULL, 0, 0);
|
|
|
|
mutex_unlock(&rt_constraints_mutex);
|
|
|
|
|
|
|
|
return ret;
|
|
|
|
}
|
2022-03-18 02:54:17 +00:00
|
|
|
#endif /* CONFIG_SYSCTL */
|
2017-06-21 18:22:02 +00:00
|
|
|
|
|
|
|
int sched_rt_can_attach(struct task_group *tg, struct task_struct *tsk)
|
|
|
|
{
|
|
|
|
/* Don't accept realtime tasks when there is no way for them to run */
|
|
|
|
if (rt_task(tsk) && tg->rt_bandwidth.rt_runtime == 0)
|
|
|
|
return 0;
|
|
|
|
|
|
|
|
return 1;
|
|
|
|
}
|
|
|
|
|
|
|
|
#else /* !CONFIG_RT_GROUP_SCHED */
|
2022-03-18 02:54:17 +00:00
|
|
|
|
|
|
|
#ifdef CONFIG_SYSCTL
|
2017-06-21 18:22:02 +00:00
|
|
|
static int sched_rt_global_constraints(void)
|
|
|
|
{
|
|
|
|
unsigned long flags;
|
|
|
|
int i;
|
|
|
|
|
|
|
|
raw_spin_lock_irqsave(&def_rt_bandwidth.rt_runtime_lock, flags);
|
|
|
|
for_each_possible_cpu(i) {
|
|
|
|
struct rt_rq *rt_rq = &cpu_rq(i)->rt;
|
|
|
|
|
|
|
|
raw_spin_lock(&rt_rq->rt_runtime_lock);
|
|
|
|
rt_rq->rt_runtime = global_rt_runtime();
|
|
|
|
raw_spin_unlock(&rt_rq->rt_runtime_lock);
|
|
|
|
}
|
|
|
|
raw_spin_unlock_irqrestore(&def_rt_bandwidth.rt_runtime_lock, flags);
|
|
|
|
|
|
|
|
return 0;
|
|
|
|
}
|
2022-03-18 02:54:17 +00:00
|
|
|
#endif /* CONFIG_SYSCTL */
|
2017-06-21 18:22:02 +00:00
|
|
|
#endif /* CONFIG_RT_GROUP_SCHED */
|
|
|
|
|
2022-03-18 02:54:17 +00:00
|
|
|
#ifdef CONFIG_SYSCTL
|
2017-06-21 18:22:02 +00:00
|
|
|
static int sched_rt_global_validate(void)
|
|
|
|
{
|
|
|
|
if (sysctl_sched_rt_period <= 0)
|
|
|
|
return -EINVAL;
|
|
|
|
|
|
|
|
if ((sysctl_sched_rt_runtime != RUNTIME_INF) &&
|
2020-04-25 10:52:48 +00:00
|
|
|
((sysctl_sched_rt_runtime > sysctl_sched_rt_period) ||
|
|
|
|
((u64)sysctl_sched_rt_runtime *
|
|
|
|
NSEC_PER_USEC > max_rt_runtime)))
|
2017-06-21 18:22:02 +00:00
|
|
|
return -EINVAL;
|
|
|
|
|
|
|
|
return 0;
|
|
|
|
}
|
|
|
|
|
|
|
|
static void sched_rt_do_global(void)
|
|
|
|
{
|
2021-12-03 03:36:18 +00:00
|
|
|
unsigned long flags;
|
|
|
|
|
|
|
|
raw_spin_lock_irqsave(&def_rt_bandwidth.rt_runtime_lock, flags);
|
2017-06-21 18:22:02 +00:00
|
|
|
def_rt_bandwidth.rt_runtime = global_rt_runtime();
|
|
|
|
def_rt_bandwidth.rt_period = ns_to_ktime(global_rt_period());
|
2021-12-03 03:36:18 +00:00
|
|
|
raw_spin_unlock_irqrestore(&def_rt_bandwidth.rt_runtime_lock, flags);
|
2017-06-21 18:22:02 +00:00
|
|
|
}
|
|
|
|
|
2022-02-15 11:45:59 +00:00
|
|
|
static int sched_rt_handler(struct ctl_table *table, int write, void *buffer,
|
2020-04-24 06:43:38 +00:00
|
|
|
size_t *lenp, loff_t *ppos)
|
2017-06-21 18:22:02 +00:00
|
|
|
{
|
|
|
|
int old_period, old_runtime;
|
|
|
|
static DEFINE_MUTEX(mutex);
|
|
|
|
int ret;
|
|
|
|
|
|
|
|
mutex_lock(&mutex);
|
|
|
|
old_period = sysctl_sched_rt_period;
|
|
|
|
old_runtime = sysctl_sched_rt_runtime;
|
|
|
|
|
|
|
|
ret = proc_dointvec(table, write, buffer, lenp, ppos);
|
|
|
|
|
|
|
|
if (!ret && write) {
|
|
|
|
ret = sched_rt_global_validate();
|
|
|
|
if (ret)
|
|
|
|
goto undo;
|
|
|
|
|
|
|
|
ret = sched_dl_global_validate();
|
|
|
|
if (ret)
|
|
|
|
goto undo;
|
|
|
|
|
|
|
|
ret = sched_rt_global_constraints();
|
|
|
|
if (ret)
|
|
|
|
goto undo;
|
|
|
|
|
|
|
|
sched_rt_do_global();
|
|
|
|
sched_dl_do_global();
|
|
|
|
}
|
|
|
|
if (0) {
|
|
|
|
undo:
|
|
|
|
sysctl_sched_rt_period = old_period;
|
|
|
|
sysctl_sched_rt_runtime = old_runtime;
|
|
|
|
}
|
|
|
|
mutex_unlock(&mutex);
|
|
|
|
|
|
|
|
return ret;
|
|
|
|
}
|
|
|
|
|
2022-02-15 11:46:01 +00:00
|
|
|
static int sched_rr_handler(struct ctl_table *table, int write, void *buffer,
|
2020-04-24 06:43:38 +00:00
|
|
|
size_t *lenp, loff_t *ppos)
|
2017-06-21 18:22:02 +00:00
|
|
|
{
|
|
|
|
int ret;
|
|
|
|
static DEFINE_MUTEX(mutex);
|
|
|
|
|
|
|
|
mutex_lock(&mutex);
|
|
|
|
ret = proc_dointvec(table, write, buffer, lenp, ppos);
|
|
|
|
/*
|
|
|
|
* Make sure that internally we keep jiffies.
|
|
|
|
* Also, writing zero resets the timeslice to default:
|
|
|
|
*/
|
|
|
|
if (!ret && write) {
|
|
|
|
sched_rr_timeslice =
|
|
|
|
sysctl_sched_rr_timeslice <= 0 ? RR_TIMESLICE :
|
|
|
|
msecs_to_jiffies(sysctl_sched_rr_timeslice);
|
|
|
|
}
|
|
|
|
mutex_unlock(&mutex);
|
sched: Clean up and harmonize the coding style of the scheduler code base
A good number of small style inconsistencies have accumulated
in the scheduler core, so do a pass over them to harmonize
all these details:
- fix speling in comments,
- use curly braces for multi-line statements,
- remove unnecessary parentheses from integer literals,
- capitalize consistently,
- remove stray newlines,
- add comments where necessary,
- remove invalid/unnecessary comments,
- align structure definitions and other data types vertically,
- add missing newlines for increased readability,
- fix vertical tabulation where it's misaligned,
- harmonize preprocessor conditional block labeling
and vertical alignment,
- remove line-breaks where they uglify the code,
- add newline after local variable definitions,
No change in functionality:
md5:
1191fa0a890cfa8132156d2959d7e9e2 built-in.o.before.asm
1191fa0a890cfa8132156d2959d7e9e2 built-in.o.after.asm
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-03-03 13:01:12 +00:00
|
|
|
|
2017-06-21 18:22:02 +00:00
|
|
|
return ret;
|
|
|
|
}
|
2022-03-18 02:54:17 +00:00
|
|
|
#endif /* CONFIG_SYSCTL */
|
2017-06-21 18:22:02 +00:00
|
|
|
|
2008-06-19 12:22:24 +00:00
|
|
|
#ifdef CONFIG_SCHED_DEBUG
|
2011-10-25 08:00:11 +00:00
|
|
|
void print_rt_stats(struct seq_file *m, int cpu)
|
2008-06-19 12:22:24 +00:00
|
|
|
{
|
2011-05-14 06:20:02 +00:00
|
|
|
rt_rq_iter_t iter;
|
2008-06-19 12:22:24 +00:00
|
|
|
struct rt_rq *rt_rq;
|
|
|
|
|
|
|
|
rcu_read_lock();
|
2011-05-14 06:20:02 +00:00
|
|
|
for_each_rt_rq(rt_rq, iter, cpu_rq(cpu))
|
2008-06-19 12:22:24 +00:00
|
|
|
print_rt_rq(m, cpu, rt_rq);
|
|
|
|
rcu_read_unlock();
|
|
|
|
}
|
2008-06-24 18:09:43 +00:00
|
|
|
#endif /* CONFIG_SCHED_DEBUG */
|