linux-kernel - [PATCH 7/8] Reprogram timers only when necessary

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Message-ID: <20090615190901.GQ21741@gandalf.sssup.it>
Date:	Mon, 15 Jun 2009 21:09:02 +0200
From:	Fabio Checconi <fchecconi@...il.com>
To:	mingo@...e.hu, a.p.zijlstra@...llo.nl
Cc:	linux-kernel@...r.kernel.org
Subject: [PATCH 7/8] Reprogram timers only when necessary

Avoid unnecessary timer reprogramming when a group is at its full
capacity and it is already enqueued.  Such a group will not need
further budget recharges until it astually consumes its budget, so
do not rearm its timer immediately.
---
 kernel/sched_rt.c |   19 ++++++++++++++++++-
 1 files changed, 18 insertions(+), 1 deletions(-)

diff --git a/kernel/sched_rt.c b/kernel/sched_rt.c
index f43ce7b..a9db16b 100644
--- a/kernel/sched_rt.c
+++ b/kernel/sched_rt.c
@@ -386,6 +386,19 @@ static int do_sched_rt_period_timer(struct rt_rq *rt_rq, int overrun)
 	return idle;
 }
 
+static inline int rt_rq_needs_recharge(struct rt_rq *rt_rq)
+{
+	struct sched_rt_entity *rt_se = rt_rq->rt_se;
+
+	if (rt_rq->rt_time)
+		return 1;
+
+	if (!rt_se)
+		return 0;
+
+	return !on_rt_rq(rt_rq->rt_se);
+}
+
 static enum hrtimer_restart sched_rt_period_timer(struct hrtimer *timer)
 {
 	struct rt_rq *rt_rq = container_of(timer, struct rt_rq,
@@ -402,7 +415,8 @@ static enum hrtimer_restart sched_rt_period_timer(struct hrtimer *timer)
 		idle = do_sched_rt_period_timer(rt_rq, overrun);
 	}
 
-	return idle ? HRTIMER_NORESTART : HRTIMER_RESTART;
+	return idle || !rt_rq_needs_recharge(rt_rq) ?
+		HRTIMER_NORESTART : HRTIMER_RESTART;
 }
 
 static void start_rt_period_timer(struct rt_rq *rt_rq)
@@ -428,6 +442,9 @@ static void start_rt_period_timer(struct rt_rq *rt_rq)
 		if (overrun)
 			__do_sched_rt_period_timer(rt_rq, overrun);
 
+		if (!rt_rq_needs_recharge(rt_rq))
+			return;
+
 		soft = hrtimer_get_softexpires(&rt_rq->rt_period_timer);
 		hard = hrtimer_get_expires(&rt_rq->rt_period_timer);
 		range = ktime_to_ns(ktime_sub(hard, soft));
-- 
1.6.2.2

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