sched: Add WAKEUP_PREEMPTION feature flag, on by default

As per the recent discussion with Mike and Linus, make it easier to
test with/without this feature. No change in default behavior.

Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/n/tip-izoxq4haeg4mTognnDbwcevt@git.kernel.org

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 6b800a1..f936552 100644 (file)
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -2907,7 +2907,7 @@ static void check_preempt_wakeup(struct rq *rq, struct task_struct *p, int wake_
         * Batch and idle tasks do not preempt non-idle tasks (their preemption
         * is driven by the tick):
         */
-       if (unlikely(p->policy != SCHED_NORMAL))
+       if (unlikely(p->policy != SCHED_NORMAL) || !sched_feat(WAKEUP_PREEMPTION))
                return;
 
        find_matching_se(&se, &pse);

diff --git a/kernel/sched/features.h b/kernel/sched/features.h
index eebefca..e68e69a 100644 (file)
--- a/kernel/sched/features.h
+++ b/kernel/sched/features.h
@@ -32,6 +32,11 @@ SCHED_FEAT(LAST_BUDDY, true)
 SCHED_FEAT(CACHE_HOT_BUDDY, true)
 
 /*
+ * Allow wakeup-time preemption of the current task:
+ */
+SCHED_FEAT(WAKEUP_PREEMPTION, true)
+
+/*
  * Use arch dependent cpu power functions
  */
 SCHED_FEAT(ARCH_POWER, true)