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Subject: Re: [PATCH v3] sched/fair: simplfy the work when reweighting entity
To:     Jiang Biao <benbjiang@gmail.com>, mingo@redhat.com,
        peterz@infradead.org, juri.lelli@redhat.com,
        vincent.guittot@linaro.org
Cc:     rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de,
        linux-kernel@vger.kernel.org, Jiang Biao <benbjiang@tencent.com>
References: <20200811113209.34057-1-benbjiang@tencent.com>
From:   Dietmar Eggemann <dietmar.eggemann@arm.com>
Message-ID: <4a0e414a-7662-58f5-f9ef-b1796552b9be@arm.com>
Date:   Mon, 17 Aug 2020 14:28:00 +0200
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On 11/08/2020 13:32, Jiang Biao wrote:
> From: Jiang Biao <benbjiang@tencent.com>
> 
> The code in reweight_entity() can be simplified.
> 
> For a sched entity on the rq, the entity accounting can be replaced by
> cfs_rq instantaneous load updates currently called from within the
> entity accounting.
> 
> Even though an entity on the rq can't represent a task in
> reweight_entity() (a task is always dequeued before calling this
> function) and so the numa task accounting and the rq->cfs_tasks list
> management of the entity accounting are never called, the redundant
> cfs_rq->nr_running decrement/increment will be avoided.
> 
> Signed-off-by: Jiang Biao <benbjiang@tencent.com>
> ---
> v3<-v2: Amend commit log taking Dietmar's advice. Thx.
> v2<-v1: Amend the commit log
> 
>  kernel/sched/fair.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 04fa8dbcfa4d..18a8fc7bd0de 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -3086,7 +3086,7 @@ static void reweight_entity(struct cfs_rq *cfs_rq, struct sched_entity *se,
>  		/* commit outstanding execution time */
>  		if (cfs_rq->curr == se)
>  			update_curr(cfs_rq);
> -		account_entity_dequeue(cfs_rq, se);
> +		update_load_sub(&cfs_rq->load, se->load.weight);
>  	}
>  	dequeue_load_avg(cfs_rq, se);
>  
> @@ -3102,7 +3102,7 @@ static void reweight_entity(struct cfs_rq *cfs_rq, struct sched_entity *se,
>  
>  	enqueue_load_avg(cfs_rq, se);
>  	if (se->on_rq)
> -		account_entity_enqueue(cfs_rq, se);
> +		update_load_add(&cfs_rq->load, se->load.weight);
>  
>  }

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