linux-kernel - Re: [PATCH 4/7] sched: Track group sched

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Message-ID: <20141008111326.GB1788@e105550-lin.cambridge.arm.com>
Date:	Wed, 8 Oct 2014 12:13:26 +0100
From:	Morten Rasmussen <morten.rasmussen@....com>
To:	"bsegall@...gle.com" <bsegall@...gle.com>
Cc:	Vincent Guittot <vincent.guittot@...aro.org>,
	"peterz@...radead.org" <peterz@...radead.org>,
	"mingo@...nel.org" <mingo@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"preeti@...ux.vnet.ibm.com" <preeti@...ux.vnet.ibm.com>,
	"kamalesh@...ux.vnet.ibm.com" <kamalesh@...ux.vnet.ibm.com>,
	"linux@....linux.org.uk" <linux@....linux.org.uk>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"riel@...hat.com" <riel@...hat.com>,
	"efault@....de" <efault@....de>,
	"nicolas.pitre@...aro.org" <nicolas.pitre@...aro.org>,
	"linaro-kernel@...ts.linaro.org" <linaro-kernel@...ts.linaro.org>,
	"daniel.lezcano@...aro.org" <daniel.lezcano@...aro.org>,
	Dietmar Eggemann <Dietmar.Eggemann@....com>,
	"pjt@...gle.com" <pjt@...gle.com>
Subject: Re: [PATCH 4/7] sched: Track group sched_entity usage contributions

On Tue, Oct 07, 2014 at 09:15:39PM +0100, bsegall@...gle.com wrote:
> Vincent Guittot <vincent.guittot@...aro.org> writes:
> 
> > From: Morten Rasmussen <morten.rasmussen@....com>
> >
> > Adds usage contribution tracking for group entities. Unlike
> > se->avg.load_avg_contrib, se->avg.utilization_avg_contrib for group
> > entities is the sum of se->avg.utilization_avg_contrib for all entities on the
> > group runqueue. It is _not_ influenced in any way by the task group
> > h_load. Hence it is representing the actual cpu usage of the group, not
> > its intended load contribution which may differ significantly from the
> > utilization on lightly utilized systems.
> 
> 
> Just noting that this version also has usage disappear immediately when
> a task blocks, although it does what you probably want on migration.

Yes, as it was discussed at Ksummit, we should include blocked
usage. It gives a much more stable metric.

> Also, group-ses don't ever use their running_avg_sum so it's kinda a
> waste, but I'm not sure it's worth doing anything about.

Yeah, but since we still have to maintain runnable_avg_sum for group-ses
it isn't much that can be saved I think. Maybe avoid calling
update_entity_load_avg() from set_next_entity() for group-ses, but I'm
not sure how much it helps.
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