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 <>
Reviewed-by: Joel Fernandes (Google) <>
Cc: Joel Fernandes <>
Cc: Linus Torvalds <>
Cc: Peter Zijlstra <>
Cc: Rafael J. Wysocki <>
Cc: Thomas Gleixner <>
Signed-off-by: Ingo Molnar <>
1 file changed