linux-kernel - Re: [PATCH V2 1/1] perf/x86: Add Intel power cstate PMUs support

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Date:	Fri, 28 Aug 2015 08:10:46 -0700
From:	Stephane Eranian <eranian@...gle.com>
To:	"Liang, Kan" <kan.liang@...el.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	"mingo@...hat.com" <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	"ak@...ux.intel.com" <ak@...ux.intel.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V2 1/1] perf/x86: Add Intel power cstate PMUs support

On Fri, Aug 28, 2015 at 8:00 AM, Liang, Kan <kan.liang@...el.com> wrote:
>
>
>> On Tue, Aug 25, 2015 at 1:15 PM, Liang, Kan <kan.liang@...el.com> wrote:
>> >
>> >> >> >
>> >> >> I understand that these metrics are useful and needed however if I
>> >> >> look at the broader picture I see many PMUs doing similar things
>> >> >> or appearing different when they are actually very close. It would
>> >> >> be nice to have a more unified approach. You have RAPL (client,
>> >> >> server) which appears as the power PMU. You have the PCU uncore
>> on
>> >> >> servers which also provides C-state residency info. Yet, all these
>> >> >> appear differently and expose events with different names.
>> >> >> I think we could benefit from a more unifie approach here such
>> >> >> that you would be able to do
>> >> >>
>> >> >> $    perf stat -a -e power/c6-residency/, power/energy-pkg/
>> >> >>
>> >> >> on client and server without having to change the pmu name of the
>> >> >> event names.
>> >> >
>> >> > Yes, I agree. I'll think about it.
>> >> >
>> >
>> > Hi Stephane,
>> >
>> > I thought more about your suggestion regarding to create a unified
>> > power PMU for all related events include RAPL and residency.
>> > It looks we can benefit from a simple unified name, but it also brings
>> > too much confusion.
>> >   - cstate residency is the time of the core/socket in specific cstate.
>> >      While RAPL event is the power core/socket which consumed.
>> >      They have different concepts.
>> >   - cstate residency includes both per-core and per-socket events.
>> >      RAPL events is only per-socket. So the CPU mask is different.
>> >      It's very confused that the events in same PMU has different CPU
>> mask.
>> >
>> > So I think it should be better to use different PMUs for RAPL and
>> residency.
>> >
>> > What do you think?
>> >
>> Well, you are maybe confusing events with PMU. If you look at the core
>> PMU, it cover many events measuring vastly different aspects of the core.
>> Some events are per-thread, others are per-core.
>>
>> Here, I was thinking it would be good to have some power// PMU with
>> many events covering cstate residency, energy consumption. And yes,
>> some events would be per-socket, others per-core.
>
> So you agree to create two new cstate PMUs (per-core and per-socket) to
> cover cstate residency?
> If so, I will start to implement the V3 version for two new PMUs.
>
I did not say that. Instead I said there is some benefits in having everything
under a power// PMU, including possibly portability to other non x86
architectures.
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