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

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Date:	Thu, 6 Aug 2015 13:38:21 -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 Thu, Aug 6, 2015 at 1:25 PM, Liang, Kan <kan.liang@...el.com> wrote:
>
>> >> >> >> +static cpumask_t power_cstate_core_cpu_mask;
>> >> >> >
>> >> >> > That one typically does not need a cpumask.
>> >> >> >
>> >> >> You need to pick one CPU out of the multi-core. But it is for
>> >> >> client parts thus there is only one socket. At least this is my
>> understanding.
>> >> >>
>> >> >
>> >> > CORE_C*_RESIDENCY are available for physical processor core.
>> >> > So logical processor in same physical processor core share the same
>> >> > counter.
>> >> > I think we need the cpumask to identify the default logical
>> >> > processor which do counting.
>> >> >
>> >> Did you restrict these events to system-wide mode only?
>> >>
>> Ok, so that means that your cpumask includes one HT per physical core.
>> But then, the result is not the simple aggregation of all the N/2 CPUs.
>
> The counter counts per physical core. The result is the aggregation of
> all HT cpus in same physical core.

But then don't you need to divide by 2 to get a meaningful result?
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