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sched/rt: Fix call to cpufreq_update_util()

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With commit:

  8f111bc357 ("cpufreq/schedutil: Rewrite CPUFREQ_RT support")

the schedutil governor uses rq->rt.rt_nr_running to detect whether an
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 has not been updated yet when dequeue_top_rt_rq() is
called so schedutil still considers that an RT task is running when the
last task is dequeued. The update of rq->rt.rt_nr_running happens later
in dequeue_rt_stack().

In fact, we can take advantage of the sequence that the dequeue then
re-enqueue rt entities when a rt task is enqueued or dequeued;
As a result enqueue_top_rt_rq() is always called when a task is
enqueued or dequeued and also when groups are throttled or unthrottled.
The only place that not use enqueue_top_rt_rq() is when root rt_rq is
throttled.

Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: efault@gmx.de
Cc: juri.lelli@redhat.com
Cc: patrick.bellasi@arm.com
Cc: viresh.kumar@linaro.org
Fixes: 8f111bc357 ('cpufreq/schedutil: Rewrite CPUFREQ_RT support')
Link: http://lkml.kernel.org/r/1530021202-21695-1-git-send-email-vincent.guittot@linaro.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Vincent Guittot
2018-06-26 15:53:22 +02:00
committed by Ingo Molnar
parent d9c0ffcabd
commit 296b2ffe7f
3 changed files with 16 additions and 7 deletions
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16
kernel/sched/rt.c
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@@ -508,8 +508,11 @@ static void sched_rt_rq_dequeue(struct rt_rq *rt_rq)
rt_se = rt_rq->tg->rt_se[cpu];
if (!rt_se)
if (!rt_se) {
dequeue_top_rt_rq(rt_rq);
/* Kick cpufreq (see the comment in kernel/sched/sched.h). */
cpufreq_update_util(rq_of_rt_rq(rt_rq), 0);
}
else if (on_rt_rq(rt_se))
dequeue_rt_entity(rt_se, 0);
}
@@ -1001,8 +1004,6 @@ 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
@@ -1014,11 +1015,14 @@ enqueue_top_rt_rq(struct rt_rq *rt_rq)
if (rt_rq->rt_queued)
return;
if (rt_rq_throttled(rt_rq) || !rt_rq->rt_nr_running)
if (rt_rq_throttled(rt_rq))
return;
add_nr_running(rq, rt_rq->rt_nr_running);
rt_rq->rt_queued = 1;
if (rt_rq->rt_nr_running) {
add_nr_running(rq, rt_rq->rt_nr_running);
rt_rq->rt_queued = 1;
}
/* Kick cpufreq (see the comment in kernel/sched/sched.h). */
cpufreq_update_util(rq, 0);