linux-kernel - Re: [PATCH v2 1/3] sched/fair: Clean up attach_entity_load

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Date:	Tue, 31 May 2016 10:34:02 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Yuyang Du <yuyang.du@...el.com>
Cc:	mingo@...nel.org, linux-kernel@...r.kernel.org, bsegall@...gle.com,
	pjt@...gle.com, morten.rasmussen@....com,
	vincent.guittot@...aro.org, dietmar.eggemann@....com
Subject: Re: [PATCH v2 1/3] sched/fair: Clean up attach_entity_load_avg()

On Tue, May 31, 2016 at 06:32:54AM +0800, Yuyang Du wrote:
> +++ b/kernel/sched/fair.c
> @@ -2961,24 +2961,6 @@ static inline void update_load_avg(struct sched_entity *se, int update_tg)
>  
>  static void attach_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se)
>  {
> -	if (!sched_feat(ATTACH_AGE_LOAD))
> -		goto skip_aging;
> -
> -	/*
> -	 * If we got migrated (either between CPUs or between cgroups) we'll
> -	 * have aged the average right before clearing @last_update_time.
> -	 */
> -	if (se->avg.last_update_time) {
> -		__update_load_avg(cfs_rq->avg.last_update_time, cpu_of(rq_of(cfs_rq)),
> -				  &se->avg, 0, 0, NULL);
> -
> -		/*
> -		 * XXX: we could have just aged the entire load away if we've been
> -		 * absent from the fair class for too long.
> -		 */
> -	}
> -
> -skip_aging:
>  	se->avg.last_update_time = cfs_rq->avg.last_update_time;
>  	cfs_rq->avg.load_avg += se->avg.load_avg;
>  	cfs_rq->avg.load_sum += se->avg.load_sum;

So I'm not a big fan of this patch; the aging is a conceptual part of
attaching the load, the fact that it only happens in one callsite is a
mere 'accident'.

The other two patches look reasonable; but I'll wait until Vince has
commented on them..