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>

diff --git a/include/linux/wait.h b/include/linux/wait.h
index ed7c122cb31f407f70a36a198d5e6d9ae48c01fa..5f3efabc36f4bb27af254bd7533e6c869bb68aaa 100644 (file)
--- 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)                          \
 ({                                                                             \