linux-kernel - Re: [BUG] perf_event: semantic of PERF_SAMPLE

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Message-ID: <1314360781.11049.2.camel@twins>
Date:	Fri, 26 Aug 2011 14:13:01 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Stephane Eranian <eranian@...gle.com>
Cc:	LKML <linux-kernel@...r.kernel.org>, mingo@...e.hu,
	Robert Richter <robert.richter@....com>,
	Vince Weaver <vweaver1@...s.utk.edu>
Subject: Re: [BUG] perf_event: semantic of PERF_SAMPLE_READ unclear

On Fri, 2011-08-26 at 14:02 +0200, Stephane Eranian wrote:
> On Thu, Aug 25, 2011 at 7:32 PM, Peter Zijlstra <peterz@...radead.org> wrote:
> > On Thu, 2011-08-25 at 19:19 +0200, Stephane Eranian wrote:
> >> But the difficulty is that
> >> we cannot grab any locks, not sure we need one given the call path.
> >
> > Nah we should be able to simply iterate all siblings and update them
> > in-place, since its group members they should all be co-scheduled. The
> > only difficulty is cross pmu group members..
> >
> Are we allowing event from different PMU to be in the same event group?
> If so, is that useful?

We allow software events, which can always be scheduled, to be part of a
hardware group. We don't allow mixing of different hardware pmus.

Allowing a software event is useful if for example the hardware pmu
doesn't have a sampling interrupt.


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