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Date: Tue, 24 Mar 2015 17:10:37 +0100
From: Peter Zijlstra <peterz@infradead.org>
To: Morten Rasmussen <morten.rasmussen@arm.com>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>,
        Sai Gurrappadi <sgurrappadi@nvidia.com>,
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        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Peter Boonstoppel <pboonstoppel@nvidia.com>
Subject: Re: [RFCv3 PATCH 30/48] sched: Calculate energy consumption of
 sched_group
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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.