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SubjectRe: [REDO PATCH v7] perf/x86/amd/power: Add AMD accumulated power reporting mechanism
Hi Vince,

Thanks for asking.

On Wed, Jun 15, 2016 at 09:13:59PM -0400, Vince Weaver wrote:
>
> three questions about this functionality:
>
> 1. In theory this should also work on an amd fam16h model 30h
> processor too, correct? The current code limits things to fam15h
> even though the fam16mod30h has all the proper cpuid flags.
>

I was told this feature would be supported on fam15h 60h, 70h and
later processors before. Just checked the fam16h model 30h BKDG, yes,
it should be also supported. But I didn't test that platform, if you
confirm it works in your side. We can enable it.

> I've tested the functionality a bit and it seems to work but for
> some reason the ptsc seems to occasionally count backwards
> on my machine. Any reason that would be? (It doesn't seem to be
> an overflow, just reading the ptsc 5ms apart and the values are
> slightly lower after than before).
>

PTSC's frequency is about 100Mhz, it shouldn't be overflow.

> 2. Unless I'm misunderstanding things, the code seems to be accumulating
> Power. (see chunk below) Power is an instantaneous measurement, it
> makes no sense to add values. If you use 5W for 1ms and 10W for
> 1ms, the average power across the 2ms interval is not 15W.
>
> You can add energy, but not power.
>
> > + delta *= cpu_pwr_sample_ratio * 1000;
> > + tdelta = new_ptsc - prev_ptsc;
> > +
> > + do_div(delta, tdelta);
> > + local64_add(delta, &event->count);
>

You're right. Nice catch! The average power is per compute unit. We
cannot add the power simplely for each processor/package.

So here, the average power per package should be (delta1 + delta2 + ... + deltaN)/(tdelta_avg).
I will work out a fix. Thanks to point out.

> 3. The actual results gathered seem rediculously low. 341 seconds of
> calculation and only using 183 mWatts of power?
>

mWatts are for processor power not system power. Below data is
calculated on fam15h model 60h which is low power platform. Even
though the method has a minor mistake, the processor power should be
in mWatts field.

> > Performance counter stats for 'system wide':
> >
> > 183.44 mWatts power/power-pkg/
> >
> > 341.837270111 seconds time elapsed
> >
> > root@hr-zp:/home/ray/tip# ./tools/perf/perf stat -a -e 'power/power-pkg/' sleep 10
>

Thanks,
Rui

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