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

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Message-ID: <20180517040822.t3zkbb2pxla7jnbp@vireshk-i7>
Date:   Thu, 17 May 2018 09:38:22 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Vincent Guittot <vincent.guittot@...aro.org>
Cc:     peterz@...radead.org, mingo@...nel.org,
        linux-kernel@...r.kernel.org, patrick.bellasi@....com,
        tglx@...utronix.de, efault@....de, juri.lelli@...hat.com,
        "# v4 . 16+" <stable@...r.kernel.org>
Subject: Re: [PATCH] sched/rt: fix call to cpufreq_update_util

On 16-05-18, 20:18, Vincent Guittot wrote:
> 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;
>  

Remove this blank line as well ?

> -	/* 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

-- 
viresh