[PATCH]sched: stop hrtick timer if running task is switching from fair scheduling class to another

[Kirill Tkhai <kirill.tkhai@gmail.com>]

[PATCH]sched: stop hrtick timer if running task is switching from fair
scheduling class to another

We have to stop hrtick timer to avoid excess interrupt. Not-fair tasks
are not interested in fair's hrtick. RT class uses its own fixed
timeslice (in case of RR), which doesn't depend on current value of hrtick
timer.

Kernel tree/version/git: next-20111216

This is resending, nobody answered me in previous time.

Signed-off-by: Kirill Tkhai <kirill.tkhai@gmail.com>
---

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 211cdc5..7733ba7 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -368,7 +368,7 @@ static struct rq *this_rq_lock(void)
  * rq->lock.
  */
 
-static void hrtick_clear(struct rq *rq)
+void hrtick_clear(struct rq *rq)
 {
 	if (hrtimer_active(&rq->hrtick_timer))
 		hrtimer_cancel(&rq->hrtick_timer);
@@ -480,10 +480,6 @@ static void init_rq_hrtick(struct rq *rq)
 	rq->hrtick_timer.function = hrtick;
 }
 #else	/* CONFIG_SCHED_HRTICK */
-static inline void hrtick_clear(struct rq *rq)
-{
-}
-
 static inline void init_rq_hrtick(struct rq *rq)
 {
 }
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index a4d2b7a..b083a91 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5271,6 +5271,13 @@ static void switched_from_fair(struct rq *rq,
struct task_struct *p)
 		place_entity(cfs_rq, se, 0);
 		se->vruntime -= cfs_rq->min_vruntime;
 	}
+
+	/*
+	 * Other scheduling classes are not interested in fair's hrtick timer.
+	 */
+	if (task_current(rq, p) && sched_feat(HRTICK))
+		hrtick_clear(rq);
+
 }
 
 /*
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index d8d3613..f3c177c 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -936,6 +936,8 @@ static inline int hrtick_enabled(struct rq *rq)
 	return hrtimer_is_hres_active(&rq->hrtick_timer);
 }
 
+void hrtick_clear(struct rq *rq);
+
 void hrtick_start(struct rq *rq, u64 delay);
 
 #else
@@ -945,6 +947,10 @@ static inline int hrtick_enabled(struct rq *rq)
 	return 0;
 }
 
+static inline void hrtick_clear(struct rq *rq)
+{
+}
+
 #endif /* CONFIG_SCHED_HRTICK */
 
 #ifdef CONFIG_SMP