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

From: Patrick Bellasi <patrick.bellasi@arm.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Tejun Heo <tj@kernel.org>,
	linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org,
	Ingo Molnar <mingo@redhat.com>,
	"Rafael J . Wysocki" <rafael.j.wysocki@intel.com>,
	Paul Turner <pjt@google.com>,
	Vincent Guittot <vincent.guittot@linaro.org>,
	John Stultz <john.stultz@linaro.org>,
	Todd Kjos <tkjos@android.com>, Tim Murray <timmurray@google.com>,
	Andres Oportus <andresoportus@google.com>,
	Joel Fernandes <joelaf@google.com>,
	Juri Lelli <juri.lelli@arm.com>,
	Chris Redpath <chris.redpath@arm.com>,
	Morten Rasmussen <morten.rasmussen@arm.com>,
	Dietmar Eggemann <dietmar.eggemann@arm.com>
Subject: Re: [RFC v3 0/5] Add capacity capping support to the CPU controller
Date: Wed, 12 Apr 2017 15:43:10 +0100	[thread overview]
Message-ID: <20170412144310.GB7572@e110439-lin> (raw)
In-Reply-To: <20170412143414.2c27dakhrydl2pqb@hirez.programming.kicks-ass.net>

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