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Date:   Thu, 1 Feb 2018 17:57:49 +0100
From:   Peter Zijlstra <peterz@infradead.org>
To:     Vincent Guittot <vincent.guittot@linaro.org>
Cc:     Morten Rasmussen <morten.rasmussen@foss.arm.com>,
        Ingo Molnar <mingo@kernel.org>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        Brendan Jackman <brendan.jackman@arm.com>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>,
        Morten Rasmussen <morten.rasmussen@arm.com>
Subject: Re: [RFC PATCH 2/5] sched: Add NOHZ_STATS_KICK
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On Wed, Jan 24, 2018 at 09:25:36AM +0100, Vincent Guittot wrote:
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 898785d..ed90303 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -7356,6 +7356,17 @@ static inline bool cfs_rq_is_decayed(struct cfs_rq *cfs_rq)
>  	return true;
>  }
>  
> +static inline bool cfs_rq_has_blocked(struct cfs_rq *cfs_rq)
> +{
> +	if (cfs_rq->avg.load_avg)
> +		return true;
> +
> +	if (cfs_rq->avg.util_avg)
> +		return true;
> +
> +	return false;
> +}
> +
>  #ifdef CONFIG_FAIR_GROUP_SCHED
>  
>  static void update_blocked_averages(int cpu)
> @@ -7393,7 +7404,9 @@ static void update_blocked_averages(int cpu)
>  		 */
>  		if (cfs_rq_is_decayed(cfs_rq))
>  			list_del_leaf_cfs_rq(cfs_rq);
> -		else
> +
> +		/* Don't need periodic decay once load/util_avg are null */
> +		if (cfs_rq_has_blocked(cfs_rq))
>  			done = false;
>  	}
>  
> @@ -7463,7 +7476,7 @@ static inline void update_blocked_averages(int cpu)
>  	update_cfs_rq_load_avg(cfs_rq_clock_task(cfs_rq), cfs_rq);
>  #ifdef CONFIG_NO_HZ_COMMON
>  	rq->last_blocked_load_update_tick = jiffies;
> -	if (cfs_rq_is_decayed(cfs_rq))
> +	if (cfs_rq_has_blocked(cfs_rq))
>  		rq->has_blocked_load = 0;
>  #endif
>  	rq_unlock_irqrestore(rq, &rf);

OK makes sense; would've been even better as a separate patch :-)