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

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Message-ID: <CABPqkBTNx02J__sO89++u4B+zipi5hgCZviiz=drer9FpAMqGQ@mail.gmail.com>
Date:	Thu, 25 Aug 2011 23:24:10 +0200
From:	Stephane Eranian <eranian@...gle.com>
To:	Peter Zijlstra <peterz@...radead.org>
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 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..
>
Yes, that's what I thought, we should be able to invoke an arch callback
to update the SW counter then we proceed with perf_event_count().
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