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