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

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Message-ID: <CABPqkBRXJPMqbdxAdapc0YtqKgZZubo2iFEhsV8VxpDG4WM9Sg@mail.gmail.com>
Date:	Fri, 26 Aug 2011 14:08:07 +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

Ok, forget what I said, I think the current code is fine.

perf_output_read_group() does call event->pmu->read() which
calls x86_perf_event_update(). And this routine does read the
actual counter. So you do get the latest version possible.


On Fri, Aug 26, 2011 at 2:02 PM, Stephane Eranian <eranian@...gle.com> 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?
>
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