linux-kernel - Re: [RFC v3 0/5] Add capacity capping support to the CPU controller

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Message-ID: <20170412144310.GB7572@e110439-lin>
Date:   Wed, 12 Apr 2017 15:43:10 +0100
From:   Patrick Bellasi <patrick.bellasi@....com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Tejun Heo <tj@...nel.org>, linux-kernel@...r.kernel.org,
        linux-pm@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        Paul Turner <pjt@...gle.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        John Stultz <john.stultz@...aro.org>,
        Todd Kjos <tkjos@...roid.com>,
        Tim Murray <timmurray@...gle.com>,
        Andres Oportus <andresoportus@...gle.com>,
        Joel Fernandes <joelaf@...gle.com>,
        Juri Lelli <juri.lelli@....com>,
        Chris Redpath <chris.redpath@....com>,
        Morten Rasmussen <morten.rasmussen@....com>,
        Dietmar Eggemann <dietmar.eggemann@....com>
Subject: Re: [RFC v3 0/5] Add capacity capping support to the CPU controller

On 12-Apr 16:34, Peter Zijlstra wrote:
> On Wed, Apr 12, 2017 at 02:27:41PM +0100, Patrick Bellasi wrote:
> > On 12-Apr 14:48, Peter Zijlstra wrote:
> > > On Tue, Apr 11, 2017 at 06:58:33PM +0100, Patrick Bellasi wrote:
> > > > >     illustrated per your above points in that it affects both, while in
> > > > >     fact it actually modifies another metric, namely util_avg.
> > > > 
> > > > I don't see it modifying in any direct way util_avg.
> > > 
> > > The point is that clamps called 'capacity' are applied to util. So while
> > > you don't modify util directly, you do modify the util signal (for one
> > > consumer).
> > 
> > Right, but this consumer (i.e. schedutil) it's already translating
> > the util_avg into a next_freq (which ultimately it's a capacity).
> > 
> > Thus, I don't see a big misfit in that code path to "filter" this
> > translation with a capacity clamp.
> 
> Still strikes me as odd though.

Can you better elaborate on they why?

-- 
#include <best/regards.h>

Patrick Bellasi