linux-kernel - Re: [RFCv3 PATCH 30/48] sched: Calculate energy consumption of sched

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Message-ID: <20150324173955.GI18994@e105550-lin.cambridge.arm.com>
Date:	Tue, 24 Mar 2015 17:39:55 +0000
From:	Morten Rasmussen <morten.rasmussen@....com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Dietmar Eggemann <Dietmar.Eggemann@....com>,
	Sai Gurrappadi <sgurrappadi@...dia.com>,
	"mingo@...hat.com" <mingo@...hat.com>,
	"vincent.guittot@...aro.org" <vincent.guittot@...aro.org>,
	"yuyang.du@...el.com" <yuyang.du@...el.com>,
	"preeti@...ux.vnet.ibm.com" <preeti@...ux.vnet.ibm.com>,
	"mturquette@...aro.org" <mturquette@...aro.org>,
	"nico@...aro.org" <nico@...aro.org>,
	"rjw@...ysocki.net" <rjw@...ysocki.net>,
	Juri Lelli <Juri.Lelli@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Peter Boonstoppel <pboonstoppel@...dia.com>
Subject: Re: [RFCv3 PATCH 30/48] sched: Calculate energy consumption of
 sched_group

On Tue, Mar 24, 2015 at 04:10:37PM +0000, Peter Zijlstra wrote:
> On Tue, Mar 24, 2015 at 10:44:24AM +0000, Morten Rasmussen wrote:
> > > > Maybe remind us why this needs to be tied to sched_groups ? Why can't we
> > > > attach the energy information to the domains?
> 
> > In the current domain hierarchy you don't have domains with just one cpu
> > in them. If you attach the per-cpu energy data to the MC level domain
> > which spans the whole cluster, you break the current idea of attaching
> > information to the cpumask (currently sched_group, but could be
> > sched_domain as we discuss here) the information is associated with. You
> > would have to either introduce a level of single cpu domains at the
> > lowest level or move away from the idea of attaching data to the cpumask
> > that is associated with it.
> > 
> > Using sched_groups we do already have single cpu groups that we can
> > attach per-cpu data to, but we are missing a top level group spanning
> > the entire system for system wide energy data. So from that point of
> > view groups and domains are equally bad.
> 
> Oh urgh, good point that. Cursed if you do, cursed if you don't. Bugger.

Yeah :( I don't really care which one we choose. Adding another top
level domain with one big group spanning all cpus, but with all SD flags
disabled seems less intrusive than adding a level at the bottom.

Better ideas are very welcome.
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