linux-kernel - Re: [PATCH 1/1] Sched/fair: Improve the accuracy of sched_stat

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Message-ID: <20201014131910.GG2628@hirez.programming.kicks-ass.net>
Date:   Wed, 14 Oct 2020 15:19:10 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     qianjun.kernel@...il.com
Cc:     mingo@...hat.com, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, linux-kernel@...r.kernel.org,
        Yafang Shao <laoar.shao@...il.com>
Subject: Re: [PATCH 1/1] Sched/fair: Improve the accuracy of sched_stat_wait
 statistics

On Fri, Oct 09, 2020 at 05:25:30PM +0800, qianjun.kernel@...il.com wrote:
> From: jun qian <qianjun.kernel@...il.com>
> 
> When the sched_schedstat changes from 0 to 1, some sched se maybe
> already in the runqueue, the se->statistics.wait_start will be 0.
> So it will let the (rq_of(cfs_rq)) - se->statistics.wait_start)
> wrong. We need to avoid this scenario.
> 
> Signed-off-by: jun qian <qianjun.kernel@...il.com>
> Signed-off-by: Yafang Shao <laoar.shao@...il.com>

This SoB chain isn't valid. Did Yafang's tag need to a reviewed-by or
something?

> ---
>  kernel/sched/fair.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 1a68a05..6f8ca0c 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -906,6 +906,15 @@ static void update_curr_fair(struct rq *rq)
>  	if (!schedstat_enabled())
>  		return;
>  
> +	/*
> +	 * When the sched_schedstat changes from 0 to 1, some sched se
> +	 * maybe already in the runqueue, the se->statistics.wait_start
> +	 * will be 0.So it will let the delta wrong. We need to avoid this
> +	 * scenario.
> +	 */
> +	if (unlikely(!schedstat_val(se->statistics.wait_start)))
> +		return;
> +
>  	delta = rq_clock(rq_of(cfs_rq)) - schedstat_val(se->statistics.wait_start);
>  
>  	if (entity_is_task(se)) {
> -- 
> 1.8.3.1
>