Re: [BUG] perf_event: semantic of PERF_SAMPLE_READ unclear

[Stephane Eranian]

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@xxxxxxxxxx> wrote:
> On Thu, Aug 25, 2011 at 7:32 PM, Peter Zijlstra <peterz@xxxxxxxxxxxxx> 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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