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

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Date:	Thu, 6 Aug 2015 21:45:30 +0000
From:	"Liang, Kan" <kan.liang@...el.com>
To:	Stephane Eranian <eranian@...gle.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



> -----Original Message-----
> From: Stephane Eranian [mailto:eranian@...gle.com]
> Sent: Thursday, August 06, 2015 4:38 PM
> To: Liang, Kan
> Cc: Peter Zijlstra; mingo@...hat.com; Arnaldo Carvalho de Melo;
> ak@...ux.intel.com; LKML
> 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?

Rethink of it. I think I was unclear about the aggregation of all HT cpus
in same physical core.

physical core Cstate should equal to min(logical core C-state).
So only all logical core enters C6-state, the physical core enters C6-state,
then CORE_C6_RESIDENCY counts.

So if we only count on one logical core/HT for CORE_C6_RESIDENCY.
We don't need to divide by 2. The count result is the residency when all logical
core in C6 (some may deeper).

Thanks,
Kan