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

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Message-ID: <20140604172712.GJ13930@laptop.programming.kicks-ass.net>
Date:	Wed, 4 Jun 2014 19:27:12 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Morten Rasmussen <morten.rasmussen@....com>
Cc:	"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, 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. Although we still needed
to come up with something for Intel, because I'm not at all sure how all
that works.

> TC2 is an early development platform and somewhat different from what
> you find in end user products. TC2 actually uses the same voltage for
> all states except the highest 2-3 states. That is not typical. The
> voltage is typically slightly different for each state, however, the
> difference get bigger for higher P-states. We could probably get away
> with representing multiple states as one in the energy model if the
> voltage change is minimal.

So while I don't mind the full table, esp. if its fairly easy to
generate using that tool you spoke about, I just wondered if it made
sense to somewhat reduce it.

Now that I look at the actual .power values, you can indeed see that all
except the last two are pretty much similar in power usage.

On that, is that fluctuation measurement noise, or is that stable?
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