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

[Peter Zijlstra]

On Wed, Jun 04, 2014 at 04:42:27PM +0100, Morten Rasmussen wrote:
> 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. 

Recent Intel chips have that too; they come packaged as:

  perf stat -a -e "power/energy-cores/" -- cmd

(through the perf_event_intel_rapl.c driver), It would be ideal if the
ARM equivalent was available through a similar interface.

http://lwn.net/Articles/573602/

> 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.

That would be good I think, esp. if we can get similar perf based energy
measurement things sorted. And if we make the tool consume the machine
topology present in sysfs we can get a long way towards automating this
I think.

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