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

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Date:	Tue, 21 Jul 2015 09:08:07 +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

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.

se is the corresponding sched_entity of cfs_rq. And when we need the
runnable_load_avg, we just calculate by the expression above.

This can be thought as a lazy way to update runnable_load_avg, and we
don't need to modify __update_load_avg any more.

Regards,
Boqun
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