linux-kernel - Re: [PATCH] sched/fair: Update min_vruntime for reweight

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Date:   Mon, 20 Nov 2023 12:48:35 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Yiwei Lin <s921975628@...il.com>
Cc:     mingo@...hat.com, wuyun.abel@...edance.com,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        linux-kernel@...r.kernel.org, s921975627@...il.com
Subject: Re: [PATCH] sched/fair: Update min_vruntime for reweight_entity()
 correctly

On Fri, Nov 17, 2023 at 04:01:06PM +0800, Yiwei Lin wrote:
> Since reweight_entity() may have chance to change the weight of
> cfs_rq->curr entity, we should also update_min_vruntime() if
> this is the case
> 
> Fixes: eab03c23c2a1 ("sched/eevdf: Fix vruntime adjustment on reweight")
> Signed-off-by: Yiwei Lin <s921975628@...il.com>


Right, but as you wrote in your other patch, min_vruntime isn't all that
critical anymore. I'll go queue this in sched/core, I don't think this
warrants /urgent.

> ---
>  kernel/sched/fair.c | 20 ++++++++++----------
>  1 file changed, 10 insertions(+), 10 deletions(-)
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 07f555857..6fb89f4a3 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -3815,17 +3815,17 @@ static void reweight_entity(struct cfs_rq *cfs_rq, struct sched_entity *se,
>  	enqueue_load_avg(cfs_rq, se);
>  	if (se->on_rq) {
>  		update_load_add(&cfs_rq->load, se->load.weight);
> -		if (!curr) {
> -			/*
> -			 * The entity's vruntime has been adjusted, so let's check
> -			 * whether the rq-wide min_vruntime needs updated too. Since
> -			 * the calculations above require stable min_vruntime rather
> -			 * than up-to-date one, we do the update at the end of the
> -			 * reweight process.
> -			 */
> +		if (!curr)
>  			__enqueue_entity(cfs_rq, se);
> -			update_min_vruntime(cfs_rq);
> -		}
> +
> +		/*
> +		 * The entity's vruntime has been adjusted, so let's check
> +		 * whether the rq-wide min_vruntime needs updated too. Since
> +		 * the calculations above require stable min_vruntime rather
> +		 * than up-to-date one, we do the update at the end of the
> +		 * reweight process.
> +		 */
> +		update_min_vruntime(cfs_rq);
>  	}
>  }
>  
> -- 
> 2.34.1
>