linux-kernel - Re: [RFC PATCH 06/16] arm: topology: Define TC2 sched energy and provide it to scheduler

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Date:	Fri, 6 Jun 2014 22:52:49 -0400 (EDT)
From:	Nicolas Pitre <nicolas.pitre@...aro.org>
To:	Peter Zijlstra <peterz@...radead.org>
cc:	Morten Rasmussen <morten.rasmussen@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"mingo@...nel.org" <mingo@...nel.org>,
	"rjw@...ysocki.net" <rjw@...ysocki.net>,
	"vincent.guittot@...aro.org" <vincent.guittot@...aro.org>,
	"daniel.lezcano@...aro.org" <daniel.lezcano@...aro.org>,
	"preeti@...ux.vnet.ibm.com" <preeti@...ux.vnet.ibm.com>,
	Dietmar Eggemann <Dietmar.Eggemann@....com>
Subject: Re: [RFC PATCH 06/16] arm: topology: Define TC2 sched energy and
 provide it to scheduler

On Wed, 4 Jun 2014, Peter Zijlstra wrote:

> On Wed, Jun 04, 2014 at 05:02:30PM +0100, Morten Rasmussen wrote:
> > On Tue, Jun 03, 2014 at 12:50:15PM +0100, Peter Zijlstra wrote:
> > > On Fri, May 23, 2014 at 07:16:33PM +0100, Morten Rasmussen wrote:
> > > > +static struct capacity_state cap_states_cluster_a7[] = {
> > > > +	/* Cluster only power */
> > > > +	 { .cap =  358, .power = 2967, }, /*  350 MHz */
> > > > +	 { .cap =  410, .power = 2792, }, /*  400 MHz */
> > > > +	 { .cap =  512, .power = 2810, }, /*  500 MHz */
> > > > +	 { .cap =  614, .power = 2815, }, /*  600 MHz */
> > > > +	 { .cap =  717, .power = 2919, }, /*  700 MHz */
> > > > +	 { .cap =  819, .power = 2847, }, /*  800 MHz */
> > > > +	 { .cap =  922, .power = 3917, }, /*  900 MHz */
> > > > +	 { .cap = 1024, .power = 4905, }, /* 1000 MHz */
> > > > +	};
> > > 
> > > So one thing I remember was that we spoke about restricting this to
> > > frequency levels where the voltage changed.
> > > 
> > > Because voltage jumps were the biggest factor to energy usage.
> > > 
> > > Any word on that?
> > 
> > Since we don't drive P-state changes from the scheduler, I think we
> > could leave out P-states from the table without too much trouble. Good
> > point.
> 
> Well, we eventually want to go there I think.

People within Linaro have initial code for this.  Should be posted as an 
RFC soon.

> Although we still needed
> to come up with something for Intel, because I'm not at all sure how all
> that works.

Our initial code reuse whatever existing platform specific cpufreq 
drivers.  The idea is to bypass the cpufreq governors.

If Intel hardware doesn't provide/allow much control here then the 
platform driver should already tell the cpufreq core (and by extension 
the scheduler) about the extent of what can be done.


Nicolas
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