linux-kernel - Re: [PATCH 1/3] sched/fair: skip idle cfs

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Date:   Wed, 06 Jan 2021 15:13:31 +0000
From:   Valentin Schneider <valentin.schneider@....com>
To:     Vincent Guittot <vincent.guittot@...aro.org>, mingo@...hat.com,
        peterz@...radead.org, juri.lelli@...hat.com,
        dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
        mgorman@...e.de, bristot@...hat.com, linux-kernel@...r.kernel.org
Cc:     Vincent Guittot <vincent.guittot@...aro.org>
Subject: Re: [PATCH 1/3] sched/fair: skip idle cfs_rq

On 06/01/21 14:34, Vincent Guittot wrote:
> Don't waste time checking whether an idle cfs_rq could be the busiest
> queue. Furthermore, this can end up selecting a cfs_rq with a high load
> but being idle in case of migrate_load.
>
> Signed-off-by: Vincent Guittot <vincent.guittot@...aro.org>

Makes sense to me.

Reviewed-by: Valentin Schneider <valentin.schneider@....com>

> ---
>  kernel/sched/fair.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 04a3ce20da67..5428b8723e61 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -9389,8 +9389,11 @@ static struct rq *find_busiest_queue(struct lb_env *env,
>  		if (rt > env->fbq_type)
>  			continue;
>  
> -		capacity = capacity_of(i);
>  		nr_running = rq->cfs.h_nr_running;
> +		if (!nr_running)
> +			continue;
> +
> +		capacity = capacity_of(i);
>  
>  		/*
>  		 * For ASYM_CPUCAPACITY domains, don't pick a CPU that could
> -- 
> 2.17.1