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

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Message-ID: <20160804150038.GQ6862@twins.programming.kicks-ass.net>
Date:	Thu, 4 Aug 2016 17:00:38 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	David Carrillo-Cisneros <davidcc@...gle.com>
Cc:	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 Mon, Aug 01, 2016 at 07:44:54PM -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?