linux-kernel - Re: Why is PERF_FORMAT_GROUP incompatible with inherited events?

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Message-ID: <1266151107.5273.629.camel@laptop>
Date:	Sun, 14 Feb 2010 13:38:27 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Paul Mackerras <paulus@...ba.org>
Cc:	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
	fweisbec@...il.com, Dave Wootton <dwootton@...ibm.com>
Subject: Re: Why is PERF_FORMAT_GROUP incompatible with inherited events?

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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