[PATCH v2] sched/wait: use freezable_schedule when possible

[PATCH v2] sched/wait: use freezable_schedule when possible

[Hugo Lefeuvre]

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.

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>
---
Changes in v2:
  - Add test results to commit message.
  - Split from initial patch set[0] since this patch can go in separately
    [0] https://lkml.org/lkml/2019/2/1/19

 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

Re: [PATCH v2] sched/wait: use freezable_schedule when possible

[Joel Fernandes]

On Thu, Feb 07, 2019 at 09:03:52PM +0100, Hugo Lefeuvre wrote:
> 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.
> 
> 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.
> 

Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>


> Signed-off-by: Hugo Lefeuvre <hle@owl.eu.com>
> ---
> Changes in v2:
>   - Add test results to commit message.
>   - Split from initial patch set[0] since this patch can go in separately
>     [0] https://lkml.org/lkml/2019/2/1/19
> 
>  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

[tip:sched/core] sched/wait: Use freezable_schedule() when possible

[tip-bot for Hugo Lefeuvre]

Commit-ID:  2b9c2a4859ad5ac7b5a28e9db28c3e618760fe8c
Gitweb:     https://git.kernel.org/tip/2b9c2a4859ad5ac7b5a28e9db28c3e618760fe8c
Author:     Hugo Lefeuvre <hle@owl.eu.com>
AuthorDate: Thu, 7 Feb 2019 21:03:52 +0100
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Mon, 11 Feb 2019 08:34:04 +0100

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>
---
 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)				\
 ({										\