linux-kernel - Re: [PATCH v5 0/2] perf: use hrtimer for event multiplexing

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Message-ID: <20130322173326.GN19692@tassilo.jf.intel.com>
Date:	Fri, 22 Mar 2013 10:33:26 -0700
From:	Andi Kleen <ak@...ux.intel.com>
To:	Stephane Eranian <eranian@...gle.com>
Cc:	linux-kernel@...r.kernel.org, peterz@...radead.org, mingo@...e.hu,
	acme@...hat.com, jolsa@...hat.com, namhyung.kim@....com
Subject: Re: [PATCH v5 0/2] perf: use hrtimer for event multiplexing

On Fri, Mar 22, 2013 at 11:51:37AM +0100, Stephane Eranian wrote:
> The current scheme of using the timer tick was fine
> for per-thread events. However, it was causing
> bias issues in system-wide mode (including for
> uncore PMUs). Event groups would not get their
> fair share of runtime on the PMU. With tickless
> kernels, if a core is idle there is no timer tick,
> and thus no event rotation (multiplexing). However,
> there are events (especially uncore events) which do
> count even though cores are asleep.

Would it be possible to only do this when uncore events
are active? Otherwise it may have a large power cost
and actually change results, as the core counters
will tick more.

-Andi
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