linux-kernel - [PATCH] sched/rt: fix call to cpufreq_update

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Date:   Wed, 16 May 2018 20:18:39 +0200
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     peterz@...radead.org, mingo@...nel.org,
        linux-kernel@...r.kernel.org
Cc:     patrick.bellasi@....com, viresh.kumar@...aro.org,
        tglx@...utronix.de, efault@....de, juri.lelli@...hat.com,
        Vincent Guittot <vincent.guittot@...aro.org>,
        "# v4 . 16+" <stable@...r.kernel.org>
Subject: [PATCH] sched/rt: fix call to cpufreq_update_util

With commit 8f111bc357aa ("cpufreq/schedutil: Rewrite CPUFREQ_RT support")
schedutil governor uses rq->rt.rt_nr_running to detect whether a RT task is
currently running on the CPU and to set frequency to max if necessary.
cpufreq_update_util() is called in enqueue/dequeue_top_rt_rq() but
rq->rt.rt_nr_running as not been updated yet when dequeue_top_rt_rq() is
called so schedutil still considers that a RT task is running when the
last task is dequeued. The update of rq->rt.rt_nr_running happens later
in dequeue_rt_stack()

Fixes: 8f111bc357aa ('cpufreq/schedutil: Rewrite CPUFREQ_RT support')
Cc: <stable@...r.kernel.org> # v4.16+
Signed-off-by: Vincent Guittot <vincent.guittot@...aro.org>
---
 kernel/sched/rt.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 7aef6b4..6e74d3d 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -1001,8 +1001,6 @@ dequeue_top_rt_rq(struct rt_rq *rt_rq)
 	sub_nr_running(rq, rt_rq->rt_nr_running);
 	rt_rq->rt_queued = 0;
 
-	/* Kick cpufreq (see the comment in kernel/sched/sched.h). */
-	cpufreq_update_util(rq, 0);
 }
 
 static void
@@ -1288,6 +1286,9 @@ static void dequeue_rt_stack(struct sched_rt_entity *rt_se, unsigned int flags)
 		if (on_rt_rq(rt_se))
 			__dequeue_rt_entity(rt_se, flags);
 	}
+
+	/* Kick cpufreq (see the comment in kernel/sched/sched.h). */
+	cpufreq_update_util(rq_of_rt_rq(rt_rq_of_se(back)), 0);
 }
 
 static void enqueue_rt_entity(struct sched_rt_entity *rt_se, unsigned int flags)
-- 
2.7.4