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

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Date:	Wed, 4 Jun 2014 16:42:27 +0100
From:	Morten Rasmussen <morten.rasmussen@....com>
To:	Peter Zijlstra <peterz@...radead.org>
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 Tue, Jun 03, 2014 at 12:44:28PM +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 */
> > +	};
> > +
> > +static struct capacity_state cap_states_cluster_a15[] = {
> > +	/* Cluster only power */
> > +	 { .cap =  840, .power =  7920, }, /*  500 MHz */
> > +	 { .cap = 1008, .power =  8165, }, /*  600 MHz */
> > +	 { .cap = 1176, .power =  8172, }, /*  700 MHz */
> > +	 { .cap = 1343, .power =  8195, }, /*  800 MHz */
> > +	 { .cap = 1511, .power =  8265, }, /*  900 MHz */
> > +	 { .cap = 1679, .power =  8446, }, /* 1000 MHz */
> > +	 { .cap = 1847, .power = 11426, }, /* 1100 MHz */
> > +	 { .cap = 2015, .power = 15200, }, /* 1200 MHz */
> > +	};
> 
> 
> So how did you obtain these numbers? Did you use numbers provided by the
> hardware people, or did you run a particular benchmark and record the
> power usage?
>
> Does that benchmark do some actual work (as opposed to a while(1) loop)
> to keep more silicon lit up?

Hardware people don't like sharing data, so I did my own measurements
and calculations to get the numbers above.

ARM TC2 has on-chip energy counters for counting energy consumed by the
A7 and A15 clusters. They are fairly accurate. I used sysbench cpu
benchmark as test workload for the above numbers. sysbench might not be
a representative workload, but it is easy to use. I think, ideally,
vendors would run their own mix of workloads they care about and derrive
their numbers for their platform based on that.

> If you have a setup for measuring these, should we try and publish that
> too so that people can run it on their platform and provide these
> numbers?

The workload setup I used quite simple. I ran sysbench with taskset with
different numbers of threads to extrapolate power consumed by each
individual cpu and how much comes from just powering on the domain.

Measuring the actual power is very platform specific. Developing a fully
automated tool do it for any given platform isn't straigt forward, but
I'm happy to share how I did it. I can add a description of the method I
used on TC2 to the documentation so others can use it as reference.
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