linux-kernel - Re: [PATCH 2/3] perf/core: introduce pmu_event_flags and PMUEF_READ_CPU

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Date:	Thu, 4 Aug 2016 10:49:30 -0700
From:	David Carrillo-Cisneros <davidcc@...gle.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	linux-kernel <linux-kernel@...r.kernel.org>,
	"x86@...nel.org" <x86@...nel.org>, Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andi Kleen <ak@...ux.intel.com>,
	Kan Liang <kan.liang@...el.com>, Paul Turner <pjt@...gle.com>,
	Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH 2/3] perf/core: introduce pmu_event_flags and PMUEF_READ_CPU_PKG

On Thu, Aug 4, 2016 at 10:27 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> On Thu, Aug 04, 2016 at 10:23:43AM -0700, David Carrillo-Cisneros wrote:
>> >> Introduce the flag PMUEF_READ_CPU_PKG, useful for uncore events, that
>> >> allows a PMU to signal the generic perf code that an event is readable
>> >> on the current CPU if the event is:
>> >>   - active in a CPU in the same package as the current CPU (local CPU)
>> >
>> > Ok that I get..
>> >
>> >>   - not active but is attached to a CPU (i.e. event->cpu != -1) in the
>> >>   same package as the current CPU.
>> >
>> > but this, not so much. Why would you want to read an inactive counter?
>>
>> Uncore counters are active even if its event is not.
>
> Not in general they are not, and if they are (freerunning msr counters
> for example) we should not include the counts when the event is
> inactive.
>
True that. I conflated Intel CQM specific behavior with other uncore
(In CQM we want to read when the event is inactive). I'll fix that in
next version.