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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2005-04-16 22:20:36 +00:00
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#ifndef _linux_POSIX_TIMERS_H
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#define _linux_POSIX_TIMERS_H
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#include <linux/spinlock.h>
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#include <linux/list.h>
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timers: Posix interface for alarm-timers
This patch exposes alarm-timers to userland via the posix clock
and timers interface, using two new clockids: CLOCK_REALTIME_ALARM
and CLOCK_BOOTTIME_ALARM. Both clockids behave identically to
CLOCK_REALTIME and CLOCK_BOOTTIME, respectively, but timers
set against the _ALARM suffixed clockids will wake the system if
it is suspended.
Some background can be found here:
https://lwn.net/Articles/429925/
The concept for Alarm-timers was inspired by the Android Alarm
driver (by Arve Hjønnevåg) found in the Android kernel tree.
See: http://android.git.kernel.org/?p=kernel/common.git;a=blob;f=drivers/rtc/alarm.c;h=1250edfbdf3302f5e4ea6194847c6ef4bb7beb1c;hb=android-2.6.36
While the in-kernel interface is pretty similar between
alarm-timers and Android alarm driver, the user-space interface
for the Android alarm driver is via ioctls to a new char device.
As mentioned above, I've instead chosen to export this functionality
via the posix interface, as it seemed a little simpler and avoids
creating duplicate interfaces to things like CLOCK_REALTIME and
CLOCK_MONOTONIC under alternate names (ie:ANDROID_ALARM_RTC and
ANDROID_ALARM_SYSTEMTIME).
The semantics of the Android alarm driver are different from what
this posix interface provides. For instance, threads other then
the thread waiting on the Android alarm driver are able to modify
the alarm being waited on. Also this interface does not allow
the same wakelock semantics that the Android driver provides
(ie: kernel takes a wakelock on RTC alarm-interupt, and holds it
through process wakeup, and while the process runs, until the
process either closes the char device or calls back in to wait
on a new alarm).
One potential way to implement similar semantics may be via
the timerfd infrastructure, but this needs more research.
There may also need to be some sort of sysfs system level policy
hooks that allow alarm timers to be disabled to keep them
from firing at inappropriate times (ie: laptop in a well insulated
bag, mid-flight).
CC: Arve Hjønnevåg <arve@android.com>
CC: Thomas Gleixner <tglx@linutronix.de>
CC: Alessandro Zummo <a.zummo@towertech.it>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: John Stultz <john.stultz@linaro.org>
2011-01-11 17:54:33 +00:00
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#include <linux/alarmtimer.h>
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2019-08-27 19:31:02 +00:00
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#include <linux/timerqueue.h>
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2020-07-30 10:14:06 +00:00
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#include <linux/task_work.h>
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2005-04-16 22:20:36 +00:00
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2019-08-19 14:31:42 +00:00
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struct kernel_siginfo;
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struct task_struct;
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2013-06-28 00:06:42 +00:00
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2011-02-01 13:52:32 +00:00
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/*
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* Bit fields within a clockid:
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*
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* The most significant 29 bits hold either a pid or a file descriptor.
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*
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* Bit 2 indicates whether a cpu clock refers to a thread or a process.
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*
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* Bits 1 and 0 give the type: PROF=0, VIRT=1, SCHED=2, or FD=3.
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*
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* A clockid is invalid if bits 2, 1, and 0 are all set.
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*/
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2005-04-16 22:20:36 +00:00
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#define CPUCLOCK_PID(clock) ((pid_t) ~((clock) >> 3))
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#define CPUCLOCK_PERTHREAD(clock) \
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(((clock) & (clockid_t) CPUCLOCK_PERTHREAD_MASK) != 0)
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2011-02-01 13:52:35 +00:00
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2005-04-16 22:20:36 +00:00
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#define CPUCLOCK_PERTHREAD_MASK 4
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#define CPUCLOCK_WHICH(clock) ((clock) & (clockid_t) CPUCLOCK_CLOCK_MASK)
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#define CPUCLOCK_CLOCK_MASK 3
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#define CPUCLOCK_PROF 0
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#define CPUCLOCK_VIRT 1
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#define CPUCLOCK_SCHED 2
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#define CPUCLOCK_MAX 3
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2011-02-01 13:52:32 +00:00
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#define CLOCKFD CPUCLOCK_MAX
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#define CLOCKFD_MASK (CPUCLOCK_PERTHREAD_MASK|CPUCLOCK_CLOCK_MASK)
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2005-04-16 22:20:36 +00:00
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2017-12-29 03:11:36 +00:00
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static inline clockid_t make_process_cpuclock(const unsigned int pid,
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const clockid_t clock)
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{
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return ((~pid) << 3) | clock;
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}
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static inline clockid_t make_thread_cpuclock(const unsigned int tid,
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const clockid_t clock)
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{
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return make_process_cpuclock(tid, clock | CPUCLOCK_PERTHREAD_MASK);
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}
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2005-04-16 22:20:36 +00:00
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2017-12-29 03:11:36 +00:00
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static inline clockid_t fd_to_clockid(const int fd)
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{
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return make_process_cpuclock((unsigned int) fd, CLOCKFD);
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}
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static inline int clockid_to_fd(const clockid_t clk)
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{
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return ~(clk >> 3);
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}
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2011-02-01 13:52:35 +00:00
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2019-08-21 19:09:04 +00:00
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#ifdef CONFIG_POSIX_TIMERS
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2019-08-26 18:22:24 +00:00
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2019-08-27 19:31:02 +00:00
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/**
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* cpu_timer - Posix CPU timer representation for k_itimer
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* @node: timerqueue node to queue in the task/sig
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* @head: timerqueue head on which this timer is queued
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* @task: Pointer to target task
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* @elist: List head for the expiry list
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* @firing: Timer is currently firing
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*/
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struct cpu_timer {
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struct timerqueue_node node;
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struct timerqueue_head *head;
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2020-02-28 17:11:06 +00:00
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struct pid *pid;
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2019-08-27 19:31:02 +00:00
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struct list_head elist;
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int firing;
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};
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static inline bool cpu_timer_enqueue(struct timerqueue_head *head,
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struct cpu_timer *ctmr)
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{
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ctmr->head = head;
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return timerqueue_add(head, &ctmr->node);
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}
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static inline void cpu_timer_dequeue(struct cpu_timer *ctmr)
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{
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2019-09-05 12:03:40 +00:00
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if (ctmr->head) {
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2019-08-27 19:31:02 +00:00
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timerqueue_del(ctmr->head, &ctmr->node);
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2019-09-05 12:03:40 +00:00
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ctmr->head = NULL;
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}
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2019-08-27 19:31:02 +00:00
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}
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static inline u64 cpu_timer_getexpires(struct cpu_timer *ctmr)
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{
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return ctmr->node.expires;
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}
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static inline void cpu_timer_setexpires(struct cpu_timer *ctmr, u64 exp)
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{
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ctmr->node.expires = exp;
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}
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2019-08-21 19:09:04 +00:00
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/**
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2019-08-26 18:22:24 +00:00
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* posix_cputimer_base - Container per posix CPU clock
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* @nextevt: Earliest-expiration cache
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2019-08-27 19:31:02 +00:00
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* @tqhead: timerqueue head for cpu_timers
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2019-08-26 18:22:24 +00:00
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*/
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struct posix_cputimer_base {
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u64 nextevt;
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2019-08-27 19:31:02 +00:00
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struct timerqueue_head tqhead;
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2019-08-26 18:22:24 +00:00
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};
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/**
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* posix_cputimers - Container for posix CPU timer related data
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* @bases: Base container for posix CPU clocks
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2019-08-21 19:09:24 +00:00
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* @timers_active: Timers are queued.
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* @expiry_active: Timer expiry is active. Used for
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* process wide timers to avoid multiple
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* task trying to handle expiry concurrently
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2019-08-21 19:09:04 +00:00
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*
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* Used in task_struct and signal_struct
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*/
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struct posix_cputimers {
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2019-08-26 18:22:24 +00:00
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struct posix_cputimer_base bases[CPUCLOCK_MAX];
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2019-08-21 19:09:24 +00:00
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unsigned int timers_active;
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unsigned int expiry_active;
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2019-08-21 19:09:04 +00:00
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};
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2020-07-30 10:14:06 +00:00
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/**
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* posix_cputimers_work - Container for task work based posix CPU timer expiry
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* @work: The task work to be scheduled
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* @scheduled: @work has been scheduled already, no further processing
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*/
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struct posix_cputimers_work {
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struct callback_head work;
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unsigned int scheduled;
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};
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2019-08-21 19:09:04 +00:00
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static inline void posix_cputimers_init(struct posix_cputimers *pct)
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{
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2019-08-27 19:31:02 +00:00
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memset(pct, 0, sizeof(*pct));
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2019-08-21 19:09:19 +00:00
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pct->bases[0].nextevt = U64_MAX;
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pct->bases[1].nextevt = U64_MAX;
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pct->bases[2].nextevt = U64_MAX;
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2019-08-21 19:09:04 +00:00
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}
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2019-08-21 19:09:06 +00:00
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void posix_cputimers_group_init(struct posix_cputimers *pct, u64 cpu_limit);
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static inline void posix_cputimers_rt_watchdog(struct posix_cputimers *pct,
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u64 runtime)
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{
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2019-08-26 18:22:24 +00:00
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pct->bases[CPUCLOCK_SCHED].nextevt = runtime;
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2019-08-21 19:09:06 +00:00
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}
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2019-08-21 19:09:04 +00:00
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/* Init task static initializer */
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2019-08-26 18:22:24 +00:00
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#define INIT_CPU_TIMERBASE(b) { \
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2019-08-21 19:09:19 +00:00
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.nextevt = U64_MAX, \
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2019-08-26 18:22:24 +00:00
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}
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#define INIT_CPU_TIMERBASES(b) { \
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INIT_CPU_TIMERBASE(b[0]), \
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INIT_CPU_TIMERBASE(b[1]), \
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INIT_CPU_TIMERBASE(b[2]), \
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2019-08-21 19:09:04 +00:00
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}
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#define INIT_CPU_TIMERS(s) \
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.posix_cputimers = { \
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2019-08-26 18:22:24 +00:00
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.bases = INIT_CPU_TIMERBASES(s.posix_cputimers.bases), \
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2019-08-21 19:09:04 +00:00
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},
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#else
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struct posix_cputimers { };
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2019-08-29 06:19:40 +00:00
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struct cpu_timer { };
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2019-08-21 19:09:04 +00:00
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#define INIT_CPU_TIMERS(s)
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2019-08-21 19:09:06 +00:00
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static inline void posix_cputimers_init(struct posix_cputimers *pct) { }
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static inline void posix_cputimers_group_init(struct posix_cputimers *pct,
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u64 cpu_limit) { }
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2019-08-21 19:09:04 +00:00
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#endif
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2020-07-30 10:14:06 +00:00
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#ifdef CONFIG_POSIX_CPU_TIMERS_TASK_WORK
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2021-11-01 21:06:15 +00:00
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void clear_posix_cputimers_work(struct task_struct *p);
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2020-07-30 10:14:06 +00:00
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void posix_cputimers_init_work(void);
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#else
|
2021-11-01 21:06:15 +00:00
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static inline void clear_posix_cputimers_work(struct task_struct *p) { }
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2020-07-30 10:14:06 +00:00
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static inline void posix_cputimers_init_work(void) { }
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#endif
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2005-04-16 22:20:36 +00:00
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#define REQUEUE_PENDING 1
|
2017-05-30 21:15:40 +00:00
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/**
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* struct k_itimer - POSIX.1b interval timer structure.
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* @list: List head for binding the timer to signals->posix_timers
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* @t_hash: Entry in the posix timer hash table
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* @it_lock: Lock protecting the timer
|
2017-05-30 21:15:44 +00:00
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* @kclock: Pointer to the k_clock struct handling this timer
|
2017-05-30 21:15:40 +00:00
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* @it_clock: The posix timer clock id
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* @it_id: The posix timer id for identifying the timer
|
2017-05-30 21:15:48 +00:00
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* @it_active: Marker that timer is active
|
2017-05-30 21:15:40 +00:00
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* @it_overrun: The overrun counter for pending signals
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* @it_overrun_last: The overrun at the time of the last delivered signal
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* @it_requeue_pending: Indicator that timer waits for being requeued on
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* signal delivery
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* @it_sigev_notify: The notify word of sigevent struct for signal delivery
|
2017-05-30 21:15:43 +00:00
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* @it_interval: The interval for periodic timers
|
2017-05-30 21:15:40 +00:00
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* @it_signal: Pointer to the creators signal struct
|
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* @it_pid: The pid of the process/task targeted by the signal
|
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* @it_process: The task to wakeup on clock_nanosleep (CPU timers)
|
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* @sigq: Pointer to preallocated sigqueue
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* @it: Union representing the various posix timer type
|
2019-07-30 22:33:54 +00:00
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* internals.
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* @rcu: RCU head for freeing the timer.
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2017-05-30 21:15:40 +00:00
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*/
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struct k_itimer {
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struct list_head list;
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struct hlist_node t_hash;
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spinlock_t it_lock;
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2017-05-30 21:15:44 +00:00
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const struct k_clock *kclock;
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2017-05-30 21:15:40 +00:00
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clockid_t it_clock;
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timer_t it_id;
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2017-05-30 21:15:48 +00:00
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int it_active;
|
2018-06-26 13:21:32 +00:00
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s64 it_overrun;
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s64 it_overrun_last;
|
2017-05-30 21:15:40 +00:00
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int it_requeue_pending;
|
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|
|
int it_sigev_notify;
|
2017-05-30 21:15:43 +00:00
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|
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ktime_t it_interval;
|
2017-05-30 21:15:40 +00:00
|
|
|
struct signal_struct *it_signal;
|
2008-12-01 22:18:13 +00:00
|
|
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union {
|
2017-05-30 21:15:40 +00:00
|
|
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struct pid *it_pid;
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|
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struct task_struct *it_process;
|
2008-12-01 22:18:13 +00:00
|
|
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};
|
2017-05-30 21:15:40 +00:00
|
|
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struct sigqueue *sigq;
|
2005-04-16 22:20:36 +00:00
|
|
|
union {
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|
|
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struct {
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2017-05-30 21:15:40 +00:00
|
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struct hrtimer timer;
|
2005-04-16 22:20:36 +00:00
|
|
|
} real;
|
2019-08-27 19:31:02 +00:00
|
|
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struct cpu_timer cpu;
|
2011-08-10 19:09:24 +00:00
|
|
|
struct {
|
2017-05-30 21:15:40 +00:00
|
|
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struct alarm alarmtimer;
|
2011-08-10 19:09:24 +00:00
|
|
|
} alarm;
|
2005-04-16 22:20:36 +00:00
|
|
|
} it;
|
2019-07-30 22:33:54 +00:00
|
|
|
struct rcu_head rcu;
|
2005-04-16 22:20:36 +00:00
|
|
|
};
|
|
|
|
|
2019-08-19 14:31:47 +00:00
|
|
|
void run_posix_cpu_timers(void);
|
2006-01-10 04:52:28 +00:00
|
|
|
void posix_cpu_timers_exit(struct task_struct *task);
|
|
|
|
void posix_cpu_timers_exit_group(struct task_struct *task);
|
|
|
|
void set_process_cpu_timer(struct task_struct *task, unsigned int clock_idx,
|
2017-01-31 03:09:35 +00:00
|
|
|
u64 *newval, u64 *oldval);
|
2005-04-16 22:20:36 +00:00
|
|
|
|
2009-08-28 12:05:12 +00:00
|
|
|
void update_rlimit_cpu(struct task_struct *task, unsigned long rlim_new);
|
timers: fix itimer/many thread hang
Overview
This patch reworks the handling of POSIX CPU timers, including the
ITIMER_PROF, ITIMER_VIRT timers and rlimit handling. It was put together
with the help of Roland McGrath, the owner and original writer of this code.
The problem we ran into, and the reason for this rework, has to do with using
a profiling timer in a process with a large number of threads. It appears
that the performance of the old implementation of run_posix_cpu_timers() was
at least O(n*3) (where "n" is the number of threads in a process) or worse.
Everything is fine with an increasing number of threads until the time taken
for that routine to run becomes the same as or greater than the tick time, at
which point things degrade rather quickly.
This patch fixes bug 9906, "Weird hang with NPTL and SIGPROF."
Code Changes
This rework corrects the implementation of run_posix_cpu_timers() to make it
run in constant time for a particular machine. (Performance may vary between
one machine and another depending upon whether the kernel is built as single-
or multiprocessor and, in the latter case, depending upon the number of
running processors.) To do this, at each tick we now update fields in
signal_struct as well as task_struct. The run_posix_cpu_timers() function
uses those fields to make its decisions.
We define a new structure, "task_cputime," to contain user, system and
scheduler times and use these in appropriate places:
struct task_cputime {
cputime_t utime;
cputime_t stime;
unsigned long long sum_exec_runtime;
};
This is included in the structure "thread_group_cputime," which is a new
substructure of signal_struct and which varies for uniprocessor versus
multiprocessor kernels. For uniprocessor kernels, it uses "task_cputime" as
a simple substructure, while for multiprocessor kernels it is a pointer:
struct thread_group_cputime {
struct task_cputime totals;
};
struct thread_group_cputime {
struct task_cputime *totals;
};
We also add a new task_cputime substructure directly to signal_struct, to
cache the earliest expiration of process-wide timers, and task_cputime also
replaces the it_*_expires fields of task_struct (used for earliest expiration
of thread timers). The "thread_group_cputime" structure contains process-wide
timers that are updated via account_user_time() and friends. In the non-SMP
case the structure is a simple aggregator; unfortunately in the SMP case that
simplicity was not achievable due to cache-line contention between CPUs (in
one measured case performance was actually _worse_ on a 16-cpu system than
the same test on a 4-cpu system, due to this contention). For SMP, the
thread_group_cputime counters are maintained as a per-cpu structure allocated
using alloc_percpu(). The timer functions update only the timer field in
the structure corresponding to the running CPU, obtained using per_cpu_ptr().
We define a set of inline functions in sched.h that we use to maintain the
thread_group_cputime structure and hide the differences between UP and SMP
implementations from the rest of the kernel. The thread_group_cputime_init()
function initializes the thread_group_cputime structure for the given task.
The thread_group_cputime_alloc() is a no-op for UP; for SMP it calls the
out-of-line function thread_group_cputime_alloc_smp() to allocate and fill
in the per-cpu structures and fields. The thread_group_cputime_free()
function, also a no-op for UP, in SMP frees the per-cpu structures. The
thread_group_cputime_clone_thread() function (also a UP no-op) for SMP calls
thread_group_cputime_alloc() if the per-cpu structures haven't yet been
allocated. The thread_group_cputime() function fills the task_cputime
structure it is passed with the contents of the thread_group_cputime fields;
in UP it's that simple but in SMP it must also safely check that tsk->signal
is non-NULL (if it is it just uses the appropriate fields of task_struct) and,
if so, sums the per-cpu values for each online CPU. Finally, the three
functions account_group_user_time(), account_group_system_time() and
account_group_exec_runtime() are used by timer functions to update the
respective fields of the thread_group_cputime structure.
Non-SMP operation is trivial and will not be mentioned further.
The per-cpu structure is always allocated when a task creates its first new
thread, via a call to thread_group_cputime_clone_thread() from copy_signal().
It is freed at process exit via a call to thread_group_cputime_free() from
cleanup_signal().
All functions that formerly summed utime/stime/sum_sched_runtime values from
from all threads in the thread group now use thread_group_cputime() to
snapshot the values in the thread_group_cputime structure or the values in
the task structure itself if the per-cpu structure hasn't been allocated.
Finally, the code in kernel/posix-cpu-timers.c has changed quite a bit.
The run_posix_cpu_timers() function has been split into a fast path and a
slow path; the former safely checks whether there are any expired thread
timers and, if not, just returns, while the slow path does the heavy lifting.
With the dedicated thread group fields, timers are no longer "rebalanced" and
the process_timer_rebalance() function and related code has gone away. All
summing loops are gone and all code that used them now uses the
thread_group_cputime() inline. When process-wide timers are set, the new
task_cputime structure in signal_struct is used to cache the earliest
expiration; this is checked in the fast path.
Performance
The fix appears not to add significant overhead to existing operations. It
generally performs the same as the current code except in two cases, one in
which it performs slightly worse (Case 5 below) and one in which it performs
very significantly better (Case 2 below). Overall it's a wash except in those
two cases.
I've since done somewhat more involved testing on a dual-core Opteron system.
Case 1: With no itimer running, for a test with 100,000 threads, the fixed
kernel took 1428.5 seconds, 513 seconds more than the unfixed system,
all of which was spent in the system. There were twice as many
voluntary context switches with the fix as without it.
Case 2: With an itimer running at .01 second ticks and 4000 threads (the most
an unmodified kernel can handle), the fixed kernel ran the test in
eight percent of the time (5.8 seconds as opposed to 70 seconds) and
had better tick accuracy (.012 seconds per tick as opposed to .023
seconds per tick).
Case 3: A 4000-thread test with an initial timer tick of .01 second and an
interval of 10,000 seconds (i.e. a timer that ticks only once) had
very nearly the same performance in both cases: 6.3 seconds elapsed
for the fixed kernel versus 5.5 seconds for the unfixed kernel.
With fewer threads (eight in these tests), the Case 1 test ran in essentially
the same time on both the modified and unmodified kernels (5.2 seconds versus
5.8 seconds). The Case 2 test ran in about the same time as well, 5.9 seconds
versus 5.4 seconds but again with much better tick accuracy, .013 seconds per
tick versus .025 seconds per tick for the unmodified kernel.
Since the fix affected the rlimit code, I also tested soft and hard CPU limits.
Case 4: With a hard CPU limit of 20 seconds and eight threads (and an itimer
running), the modified kernel was very slightly favored in that while
it killed the process in 19.997 seconds of CPU time (5.002 seconds of
wall time), only .003 seconds of that was system time, the rest was
user time. The unmodified kernel killed the process in 20.001 seconds
of CPU (5.014 seconds of wall time) of which .016 seconds was system
time. Really, though, the results were too close to call. The results
were essentially the same with no itimer running.
Case 5: With a soft limit of 20 seconds and a hard limit of 2000 seconds
(where the hard limit would never be reached) and an itimer running,
the modified kernel exhibited worse tick accuracy than the unmodified
kernel: .050 seconds/tick versus .028 seconds/tick. Otherwise,
performance was almost indistinguishable. With no itimer running this
test exhibited virtually identical behavior and times in both cases.
In times past I did some limited performance testing. those results are below.
On a four-cpu Opteron system without this fix, a sixteen-thread test executed
in 3569.991 seconds, of which user was 3568.435s and system was 1.556s. On
the same system with the fix, user and elapsed time were about the same, but
system time dropped to 0.007 seconds. Performance with eight, four and one
thread were comparable. Interestingly, the timer ticks with the fix seemed
more accurate: The sixteen-thread test with the fix received 149543 ticks
for 0.024 seconds per tick, while the same test without the fix received 58720
for 0.061 seconds per tick. Both cases were configured for an interval of
0.01 seconds. Again, the other tests were comparable. Each thread in this
test computed the primes up to 25,000,000.
I also did a test with a large number of threads, 100,000 threads, which is
impossible without the fix. In this case each thread computed the primes only
up to 10,000 (to make the runtime manageable). System time dominated, at
1546.968 seconds out of a total 2176.906 seconds (giving a user time of
629.938s). It received 147651 ticks for 0.015 seconds per tick, still quite
accurate. There is obviously no comparable test without the fix.
Signed-off-by: Frank Mayhar <fmayhar@google.com>
Cc: Roland McGrath <roland@redhat.com>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-09-12 16:54:39 +00:00
|
|
|
|
2018-09-25 09:27:20 +00:00
|
|
|
void posixtimer_rearm(struct kernel_siginfo *info);
|
2005-04-16 22:20:36 +00:00
|
|
|
#endif
|