linux-kernel - Re: [PATCH] sched/pelt: check that *_avg are null when *

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Message-ID: <438d95b4-330b-8a4b-a800-bab15db4f170@arm.com>
Date:   Thu, 3 Jun 2021 12:42:33 +0200
From:   Dietmar Eggemann <dietmar.eggemann@....com>
To:     Vincent Guittot <vincent.guittot@...aro.org>, mingo@...hat.com,
        peterz@...radead.org, juri.lelli@...hat.com, rostedt@...dmis.org,
        bsegall@...gle.com, mgorman@...e.de, bristot@...hat.com,
        linux-kernel@...r.kernel.org
Cc:     odin@...d.al
Subject: Re: [PATCH] sched/pelt: check that *_avg are null when *_sum are

On 01/06/2021 17:53, Vincent Guittot wrote:
> Check that we never break the rule that pelt's avg values are null if
> pelt's sum are.
> 
> Signed-off-by: Vincent Guittot <vincent.guittot@...aro.org>
> ---
> 
> This is what I used for patch 20210601085832.12626-1-vincent.guittot@...aro.org
> 
>  kernel/sched/fair.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index a2c30e52de76..c17feadeafcc 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -8021,6 +8021,15 @@ static inline bool cfs_rq_is_decayed(struct cfs_rq *cfs_rq)
>  	if (cfs_rq->avg.runnable_sum)
>  		return false;
>  
> +	/*
> +	 * _avg must be null when _sum are null because _avg = _sum / divider
> +	 * Make sure that rounding and/or propagation of PELT values never
> +	 * break this.
> +	 */
> +	SCHED_WARN_ON(cfs_rq->avg.load_avg ||
> +		      cfs_rq->avg.util_avg ||
> +		      cfs_rq->avg.runnable_avg);
> +
>  	return true;
>  }

Reviewed-by: Dietmar Eggemann <dietmar.eggemann@....com>