linux-kernel - Re: [PATCH v3 4/5] sched: sync a se with its cfs_rq when switching sched class to fair class

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Date:	Thu, 20 Aug 2015 14:23:40 +0900
From:	Byungchul Park <byungchul.park@....com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	mingo@...nel.org, linux-kernel@...r.kernel.org, yuyang.du@...el.com
Subject: Re: [PATCH v3 4/5] sched: sync a se with its cfs_rq when switching
 sched class to fair class

On Wed, Aug 19, 2015 at 07:12:41PM +0200, Peter Zijlstra wrote:
> On Wed, Aug 19, 2015 at 03:47:15PM +0900, byungchul.park@....com wrote:
> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > index 1be042a..3419f6c 100644
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -2711,6 +2711,17 @@ 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)
> >  {
> > +	/*
> > +	 * in case of migration and cgroup-change, more care should be taken
> > +	 * because se's cfs_rq was changed, that means calling __update_load_avg
> > +	 * with new cfs_rq->avg.last_update_time is meaningless. so we skip the
> > +	 * update here. we have to update it with prev cfs_rq just before changing
> > +	 * se's cfs_rq, and get here soon.
> > +	 */
> > +	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);
> > +
> >  	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;
> 
> you seem to have forgotten to remove the same logic from
> enqueue_entity_load_avg(), which will now call __update_load_avg()
> twice.

i am sorry for not catching what you want to say. enqueue_entity_load_avg()
calls __update_load_avg() in normal case, that is, not having changed its 
cfs_rq, while in case having changed its cfs_rq, we only need to attach the
average load assuming that __update_load_avg() was already called when its
cfs_rq was changed.

is there anything i missed? could you let me know if yes?

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