Commit 2b9c2a48 authored Feb 07, 2019 by Hugo Lefeuvre Committed by Ingo Molnar Feb 11, 2019

sched/wait: Use freezable_schedule() when possible



Replace 'schedule(); try_to_freeze();' with a call to freezable_schedule().

Tasks calling freezable_schedule() set the PF_FREEZER_SKIP flag
before calling schedule(). Unlike tasks calling schedule();
try_to_freeze() tasks calling freezable_schedule() are not awaken by
try_to_freeze_tasks(). Instead they call try_to_freeze() when they
wake up if the freeze is still underway.

It is not a problem since sleeping tasks can't do anything which isn't
allowed for a frozen task while sleeping.

The result is a potential performance gain during freeze, since less
tasks have to be awaken.

For instance on a bare Debian vm running a 4.19 stable kernel, the
number of tasks skipped in freeze_task() went up from 12 without the
patch to 32 with the patch (out of 448), an increase of > x2.5.

Signed-off-by: Hugo Lefeuvre <hle@owl.eu.com>
Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Cc: Joel Fernandes <joel@joelfernandes.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rafael J. Wysocki <rjw@rjwysocki.net>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20190207200352.GA27859@behemoth.owl.eu.com.local


Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent 9f132742

include/linux/wait.h

+3 −3

Original line number	Diff line number	Diff line
		@@ -308,7 +308,7 @@ do { \

		#define __wait_event_freezable(wq_head, condition) \
		___wait_event(wq_head, condition, TASK_INTERRUPTIBLE, 0, 0, \
		schedule(); try_to_freeze())
		freezable_schedule())

		/**
		* wait_event_freezable - sleep (or freeze) until a condition gets true
		@@ -367,7 +367,7 @@ do { \
		#define __wait_event_freezable_timeout(wq_head, condition, timeout) \
		___wait_event(wq_head, ___wait_cond_timeout(condition), \
		TASK_INTERRUPTIBLE, 0, timeout, \
		__ret = schedule_timeout(__ret); try_to_freeze())
		__ret = freezable_schedule_timeout(__ret))

		/*
		* like wait_event_timeout() -- except it uses TASK_INTERRUPTIBLE to avoid
		@@ -588,7 +588,7 @@ do { \

		#define __wait_event_freezable_exclusive(wq, condition) \
		___wait_event(wq, condition, TASK_INTERRUPTIBLE, 1, 0, \
		schedule(); try_to_freeze())
		freezable_schedule())

		#define wait_event_freezable_exclusive(wq, condition) \
		({ \

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