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 19:27:07 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	David Carrillo-Cisneros <davidcc@...gle.com>
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 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.