Subject: Re: Why is PERF_FORMAT_GROUP incompatible with inherited events?
From: Peter Zijlstra <peterz@infradead.org>
To: Paul Mackerras <paulus@samba.org>
Cc: Ingo Molnar <mingo@elte.hu>, linux-kernel@vger.kernel.org,
       fweisbec@gmail.com, Dave Wootton <dwootton@us.ibm.com>
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Date: Sun, 14 Feb 2010 13:38:27 +0100
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On Sun, 2010-02-14 at 22:33 +1100, Paul Mackerras wrote:
> 
> But we don't go and collect the count delta from children without
> PERF_FORMAT_GROUP, so why would we with it? 

Yes we do, see perf_event_read_value().

But now that I look at it we don't seem to do so in
perf_output_read_one()... I guess we should fix that.

There is of course the lock inversion in the .read() code reported by
stephane, but other than that is seems to actually support inherited &&
group just fine.

So I think if we fix that lock inversion and make the PERF_SAMPLE_READ
code look like the .read() code it should all work out.


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