linux-kernel - [PATCH 1/3] sched/wait: use freezable

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Message-ID: <d9b2ed186ed6fcacaaecd876bb66dca8fa329d8b.1548998323.git.hle@owl.eu.com>
Date:   Fri, 1 Feb 2019 06:38:05 +0100
From:   Hugo Lefeuvre <hle@....eu.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Greg Hartman <ghartman@...gle.com>,
        Alistair Strachan <strachan@...gle.com>,
        Arve Hjønnevåg <arve@...roid.com>,
        Todd Kjos <tkjos@...roid.com>,
        Martijn Coenen <maco@...roid.com>,
        Christian Brauner <christian@...uner.io>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        devel@...verdev.osuosl.org, linux-kernel@...r.kernel.org,
        Joel Fernandes <joel@...lfernandes.org>
Subject: [PATCH 1/3] sched/wait: use freezable_schedule when possible

Replace schedule(); try_to_freeze() by 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.

Signed-off-by: Hugo Lefeuvre <hle@....eu.com>
---
 include/linux/wait.h | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/include/linux/wait.h b/include/linux/wait.h
index ed7c122cb31f..5f3efabc36f4 100644
--- a/include/linux/wait.h
+++ b/include/linux/wait.h
@@ -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)				\
 ({										\
-- 
2.20.1