From: Paul Mackerras <paulus@samba.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@elte.hu>,
linux-kernel@vger.kernel.org, fweisbec@gmail.com,
Dave Wootton <dwootton@us.ibm.com>
Subject: Re: Why is PERF_FORMAT_GROUP incompatible with inherited events?
Date: Mon, 15 Feb 2010 15:56:44 +1100 [thread overview]
Message-ID: <20100215045644.GK13769@brick.ozlabs.ibm.com> (raw)
In-Reply-To: <1266151107.5273.629.camel@laptop>
On Sun, Feb 14, 2010 at 01:38:27PM +0100, Peter Zijlstra wrote:
> 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().
Ah, true, I should have read the code more carefully.
> 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.
I suppose it should give the same value as read() would, but the
possibly unbounded interrupt latency is a bit of a worry. I can't
think of a way to avoid it, though (other than not using
PERF_SAMPLE_READ with inherited sampling events :).
> 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.
Cool.
Paul.
next prev parent reply other threads:[~2010-02-15 4:56 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-02-12 3:02 Why is PERF_FORMAT_GROUP incompatible with inherited events? Paul Mackerras
2010-02-14 10:12 ` Peter Zijlstra
2010-02-14 11:33 ` Paul Mackerras
2010-02-14 12:38 ` Peter Zijlstra
2010-02-15 4:56 ` Paul Mackerras [this message]
2010-02-15 9:29 ` Peter Zijlstra
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