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Liang Chen 1c263d0e54 kthread: Do not preempt current task if it is going to call schedule() 
commit 26c7295be0 upstream.

when we create a kthread with ktrhead_create_on_cpu(),the child thread
entry is ktread.c:ktrhead() which will be preempted by the parent after
call complete(done) while schedule() is not called yet,then the parent
will call wait_task_inactive(child) but the child is still on the runqueue,
so the parent will schedule_hrtimeout() for 1 jiffy,it will waste a lot of
time,especially on startup.

  parent                             child
ktrhead_create_on_cpu()
  wait_fo_completion(&done) -----> ktread.c:ktrhead()
                             |----- complete(done);--wakeup and preempted by parent
 kthread_bind() <------------|  |-> schedule();--dequeue here
  wait_task_inactive(child)     |
   schedule_hrtimeout(1 jiffy) -|

So we hope the child just wakeup parent but not preempted by parent, and the
child is going to call schedule() soon,then the parent will not call
schedule_hrtimeout(1 jiffy) as the child is already dequeue.

The same issue for ktrhead_park()&&kthread_parkme().
This patch can save 120ms on rk312x startup with CONFIG_HZ=300.

Signed-off-by: Liang Chen <cl@rock-chips.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Link: https://lkml.kernel.org/r/20200306070133.18335-2-cl@rock-chips.com
Signed-off-by: Chanho Park <chanho61.park@samsung.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2020-08-26 10:31:00 +02:00
arch arm64: dts: marvell: espressobin: add ethernet alias 2020-08-21 11:05:39 +02:00
block block: release bip in a right way in error path 2020-07-16 08:17:23 +02:00
certs export.h: remove VMLINUX_SYMBOL() and VMLINUX_SYMBOL_STR() 2018-08-22 23:21:44 +09:00
crypto crypto: af_alg - fix use-after-free in af_alg_accept() due to bh_lock_sock() 2020-07-09 09:37:10 +02:00
Documentation dt-bindings: iio: io-channel-mux: Fix compatible string in example code 2020-08-21 11:05:30 +02:00
drivers drm/amd/display: fix pow() crashing when given base 0 2020-08-26 10:31:00 +02:00
firmware Fix built-in early-load Intel microcode alignment 2020-01-23 08:21:29 +01:00
fs jbd2: add the missing unlock_buffer() in the error path of jbd2_write_superblock() 2020-08-26 10:30:59 +02:00
include iommu/vt-d: Enforce PASID devTLB field mask 2020-08-21 11:05:36 +02:00
init printk: queue wake_up_klogd irq_work only if per-CPU areas are ready 2020-07-22 09:32:13 +02:00
ipc ipc/util.c: sysvipc_find_ipc() incorrectly updates position index 2020-05-20 08:18:40 +02:00
kernel kthread: Do not preempt current task if it is going to call schedule() 2020-08-26 10:31:00 +02:00
lib test_kmod: avoid potential double free in trigger_config_run_type() 2020-08-21 11:05:38 +02:00
LICENSES LICENSES: Remove CC-BY-SA-4.0 license text 2018-10-18 11:28:50 +02:00
mm mm, page_alloc: fix core hung in free_pcppages_bulk() 2020-08-26 10:30:59 +02:00
net mac80211: fix misplaced while instead of if 2020-08-21 11:05:32 +02:00
samples samples: bpf: Fix build error 2020-06-03 08:19:31 +02:00
scripts scripts/gdb: fix lx-symbols 'gdb.error' while loading modules 2020-07-29 10:16:51 +02:00
security Smack: prevent underflow in smk_set_cipso() 2020-08-19 08:14:59 +02:00
sound ALSA: echoaudio: Fix potential Oops in snd_echo_resume() 2020-08-21 11:05:38 +02:00
tools perf probe: Fix memory leakage when the probe point is not found 2020-08-26 10:30:58 +02:00
usr initramfs: restore default compression behavior 2020-04-13 10:44:59 +02:00
virt KVM: arm64: Synchronize sysreg state on injecting an AArch32 exception 2020-06-22 09:05:09 +02:00
.clang-format clang-format: Set IndentWrappedFunctionNames false 2018-08-01 18:38:51 +02:00
.cocciconfig
.get_maintainer.ignore
.gitattributes .gitattributes: set git diff driver for C source code files 2016-10-07 18:46:30 -07:00
.gitignore Kbuild updates for v4.17 (2nd) 2018-04-15 17:21:30 -07:00
.mailmap libnvdimm-for-4.19_misc 2018-08-25 18:13:10 -07:00
COPYING COPYING: use the new text with points to the license files 2018-03-23 12:41:45 -06:00
CREDITS 9p: remove Ron Minnich from MAINTAINERS 2018-08-17 16:20:26 -07:00
Kbuild Kbuild updates for v4.15 2017-11-17 17:45:29 -08:00
Kconfig kconfig: move the "Executable file formats" menu to fs/Kconfig.binfmt 2018-08-02 08:06:55 +09:00
MAINTAINERS MAINTAINERS: Update drm/i915 bug filing URL 2020-02-28 16:38:49 +01:00
Makefile Linux 4.19.141 2020-08-21 11:05:39 +02:00
README Docs: Added a pointer to the formatted docs to README 2018-03-21 09:02:53 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
See Documentation/00-INDEX for a list of what is contained in each file.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.