linux-kernel - Re: [PATCH v7 3/4] perf,x86: add Intel RAPL PMU support

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Date:	Fri, 29 Nov 2013 21:09:46 +0100
From:	Stephane Eranian <eranian@...gle.com>
To:	Vince Weaver <vince@...ter.net>
Cc:	Ingo Molnar <mingo@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	"mingo@...e.hu" <mingo@...e.hu>,
	"ak@...ux.intel.com" <ak@...ux.intel.com>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Jiri Olsa <jolsa@...hat.com>,
	"Yan, Zheng" <zheng.z.yan@...el.com>,
	Borislav Petkov <bp@...en8.de>,
	Maria Dimakopoulou <maria.n.dimakopoulou@...il.com>
Subject: Re: [PATCH v7 3/4] perf,x86: add Intel RAPL PMU support

On Fri, Nov 29, 2013 at 8:16 PM, Vince Weaver <vince@...ter.net> wrote:
> On Thu, 28 Nov 2013, Stephane Eranian wrote:
>
>> On Thu, Nov 28, 2013 at 1:26 PM, Ingo Molnar <mingo@...nel.org> wrote:
>> >
>> > * Vince Weaver <vince@...ter.net> wrote:
>> >
>> >> On Wed, 27 Nov 2013, Stephane Eranian wrote:
>> >>
>> >> > On Wed, Nov 27, 2013 at 7:35 PM, Vince Weaver <vince@...ter.net> wrote:
>> >>
>> >> > > So I notice PP1 (which is the GPU power on non-server chips)
>> >> > > is not supported.
>> >> > >
>> >> > > Is that just for simplicity?
>> >> > >
>> >> > Does it work on specific models only? I bet so. How to detect those?
>> >>
>> >> In general it is on the machines that don't support the DRAM measurements
>> >> (so the non-EP machines) but I don't know if there's a nice list anywhere.
>> >>
>> >> Intel manuals say:
>> >>    For a client platform, PP1 domain refers to the power plane of a
>> >>    specific device in the uncore. For server platforms, PP1 domain is not
>> >>    supported,
>> >>
>> >> usually PP1 I think maps to the embedded GPU.
>> >
>> > It would indeed be nice to expose PP1 too via the same facility -
>> > Haswell and later spends some 40% of the CPU die on the integrated GPU
>> > and people end up using it.
>> >
>> My worry is to determine if the GPU is actually enabled or even present.
>> Using the x86_model may not be enough for that.
>
> In my experience if the device is not there you just get 0s as results
> from RAPL (I've also seen this on some Sandybridge-EP machines we have
> that for whatever reason don't support the DRAM RAPL results).
>
> So in theory it would be harmless to export the values even if not
> supported.  What is the worst failure mode?  That somehow a recent CPU
> doesn't support the MSR and we get a GPF when trying to access it?
>
Yes. I think that's what you get with DRAM on client for instance.

> Vince
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