Re: [PATCH v2 1/3] sched/fair: Clean up attach_entity_load_avg()

From: Peter Zijlstra
Date: Tue May 31 2016 - 04:34:19 EST


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..