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

From: Stephane Eranian
Date: Fri Mar 22 2013 - 13:36:45 EST

On Fri, Mar 22, 2013 at 6:33 PM, Andi Kleen <ak@xxxxxxxxxxxxxxx> wrote:
> 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.
the hrtimer is activated only when multiplexing is needed
and that's for any PMU.
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