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Filename Latest commit message Latest commit date
Liang Chen 52d322f919 kthread: Do not preempt current task if it is going to call schedule() 
commit 26c7295be0c5e6da3fa45970e9748be983175b1b 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 10:40:53 +02:00
arch
block
certs
crypto
Documentation kbuild: support LLVM=1 to switch the default tools to Clang/LLVM 2020-08-26 10:40:47 +02:00
drivers drm/amd/display: fix pow() crashing when given base 0 2020-08-26 10:40:53 +02:00
fs jbd2: add the missing unlock_buffer() in the error path of jbd2_write_superblock() 2020-08-26 10:40:52 +02:00
include
init
ipc
kernel kthread: Do not preempt current task if it is going to call schedule() 2020-08-26 10:40:53 +02:00
lib
LICENSES
mm mm, page_alloc: fix core hung in free_pcppages_bulk() 2020-08-26 10:40:51 +02:00
net can: j1939: socket: j1939_sk_bind(): make sure ml_priv is allocated 2020-08-26 10:40:50 +02:00
samples
scripts
security
sound ALSA: hda/realtek: Add quirk for Samsung Galaxy Book Ion 2020-08-26 10:40:50 +02:00
tools perf probe: Fix memory leakage when the probe point is not found 2020-08-26 10:40:48 +02:00
usr
virt
.clang-format
.cocciconfig
.get_maintainer.ignore
.gitattributes
.gitignore
.mailmap
COPYING
CREDITS
Kbuild
Kconfig
MAINTAINERS
Makefile kbuild: support LLVM=1 to switch the default tools to Clang/LLVM 2020-08-26 10:40:47 +02:00
README

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.

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.