[tip:sched/urgent] sched: Add WAKEUP_PREEMPTION feature flag, on by default

[tip-bot for Ingo Molnar]

Commit-ID:  8ed92e51f99c2199c64cb33b4ba95ab12940a94c
Gitweb:     http://git.kernel.org/tip/8ed92e51f99c2199c64cb33b4ba95ab12940a94c
Author:     Ingo Molnar <mingo@xxxxxxx>
AuthorDate: Sun, 14 Oct 2012 14:28:50 +0200
Committer:  Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Tue, 16 Oct 2012 10:05:27 +0200

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@xxxxxxxxxx>
Cc: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Cc: Mike Galbraith <efault@xxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Link: http://lkml.kernel.org/n/tip-izoxq4haeg4mTognnDbwcevt@xxxxxxxxxxxxxx
---
 kernel/sched/fair.c     |    2 +-
 kernel/sched/features.h |    5 +++++
 2 files changed, 6 insertions(+), 1 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 6b800a1..f936552 100644
--- 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
--- 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)
--
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