linux-kernel - Re: [RFCv5 PATCH 11/46] sched: Remove blocked load and utilization contributions of dying tasks

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Message-ID: <20150811145847.GA20892@e105550-lin.cambridge.arm.com>
Date:	Tue, 11 Aug 2015 15:58:48 +0100
From:	Morten Rasmussen <morten.rasmussen@....com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	mingo@...hat.com, vincent.guittot@...aro.org,
	daniel.lezcano@...aro.org,
	Dietmar Eggemann <Dietmar.Eggemann@....com>,
	yuyang.du@...el.com, mturquette@...libre.com, rjw@...ysocki.net,
	Juri Lelli <Juri.Lelli@....com>, sgurrappadi@...dia.com,
	pang.xunlei@....com.cn, linux-kernel@...r.kernel.org,
	linux-pm@...r.kernel.org
Subject: Re: [RFCv5 PATCH 11/46] sched: Remove blocked load and utilization
 contributions of dying tasks

On Tue, Aug 11, 2015 at 01:39:27PM +0200, Peter Zijlstra wrote:
> On Tue, Jul 07, 2015 at 07:23:54PM +0100, Morten Rasmussen wrote:
> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > index 775b0c7..fa12ce5 100644
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -3217,6 +3217,8 @@ dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
> >  	 * Update run-time statistics of the 'current'.
> >  	 */
> >  	update_curr(cfs_rq);
> > +	if (entity_is_task(se) && task_of(se)->state == TASK_DEAD)
> > +		flags &= !DEQUEUE_SLEEP;
> >  	dequeue_entity_load_avg(cfs_rq, se, flags & DEQUEUE_SLEEP);
> >  
> >  	update_stats_dequeue(cfs_rq, se);
> 
> I know this is entirely redundant at this point (we took Yuyang's
> patches), but this is the wrong way to go about doing this.

Yes, I'm still working my way through Yuyang's changes.

> You add extra code the hot dequeue path for something that 'never'
> happens. We have the sched_class::task_dead call for that.

I don't mind using sched_class::task_dead() instead. The reason why I
didn't go that way is that we have to retake the rq->lock or mess with
cfs_rq::removed_load instead of just not adding the utilization in
the first place when we have the rq->lock.

Anyway, it is probably redundant by now. I will check Yuyang's code to
see if he already fixed this problem.
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