linux-kernel - Re: [PATCH v10 6/7] sched: Provide runnable_load_avg back to cfs

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Message-ID: <20150721102956.GA5380@fixme-laptop.cn.ibm.com>
Date:	Tue, 21 Jul 2015 18:29:56 +0800
From:	Boqun Feng <boqun.feng@...il.com>
To:	Yuyang Du <yuyang.du@...el.com>
Cc:	mingo@...nel.org, peterz@...radead.org,
	linux-kernel@...r.kernel.org, pjt@...gle.com, bsegall@...gle.com,
	morten.rasmussen@....com, vincent.guittot@...aro.org,
	dietmar.eggemann@....com, umgwanakikbuti@...il.com,
	len.brown@...el.com, rafael.j.wysocki@...el.com,
	arjan@...ux.intel.com, fengguang.wu@...el.com
Subject: Re: [PATCH v10 6/7] sched: Provide runnable_load_avg back to cfs_rq

On Tue, Jul 21, 2015 at 06:18:46PM +0800, Boqun Feng wrote:
> On Tue, Jul 21, 2015 at 08:44:01AM +0800, Yuyang Du wrote:
> > On Tue, Jul 21, 2015 at 09:08:07AM +0800, Boqun Feng wrote:
> > > Hi Yuyang,
> > > 
> > > On Wed, Jul 15, 2015 at 08:04:41AM +0800, Yuyang Du wrote:
> > > > The cfs_rq's load_avg is composed of runnable_load_avg and blocked_load_avg.
> > > > Before this series, sometimes the runnable_load_avg is used, and sometimes
> > > > the load_avg is used. Completely replacing all uses of runnable_load_avg
> > > > with load_avg may be too big a leap, i.e., the blocked_load_avg is concerned
> > > > to result in overrated load. Therefore, we get runnable_load_avg back.
> > > > 
> > > > The new cfs_rq's runnable_load_avg is improved to be updated with all of the
> > > > runnable sched_eneities at the same time, so the one sched_entity updated and
> > > > the others stale problem is solved.
> > > > 
> > > 
> > > How about tracking cfs_rq's blocked_load_avg instead of
> > > runnable_load_avg, because, AFAICS:
> > > 
> > > cfs_rq->runnable_load_avg = se->avg.load_avg - cfs_rq->blocked_load_avg.
> > 
> > No, cfs_rq->runnable_load_avg = cfs_rq->avg.load_avg - cfs_rq->blocked_load_avg,
> > without rounding errors and the like.
> >  
> 
> Oh, sorry.. yeah, you're right here.
> 

The point is that you have already tracked the sum of runnable_load_avg
and blocked_load_avg in cfs_rq->avg.load_avg. If you're going to track
part of the sum, you'd better track the one that's updated less
frequently, right?

Anyway, this idea just comes into my mind. I wonder which is udpated
less frequently myself too. ;-) So I ask to see whether there is
something we can improve.

Regards,
Boqun

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