linux-kernel - [BUG(?)] perf_events: combining multiple tracepoint events into a group produces no counts on member events

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Date:	Tue, 30 Nov 2010 17:00:16 -0800
From:	Corey Ashford <cjashfor@...ux.vnet.ibm.com>
To:	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Frederic Weisbecker <fweisbec@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Stephane Eranian <eranian@...gle.com>
Subject: [BUG(?)] perf_events: combining multiple tracepoint events into a
 group produces no counts on member events

Hi,

I'm not sure that what I'm seeing is a bug, or was something intentional.

If I place multiple tracepoint events into a group and measure counts of 
these events on a process, I get no counts for the tracepoint events 
other than the group leader.

Is this expected behavior?

It's not clear to me why this should be the case; grouping shouldn't 
have any ill effects on tracepoint events, from my understanding.

I noticed this because my private version of the perf tool has the event 
group patch https://lkml.org/lkml/2010/11/24/584 as well as the patch 
which fixes the parsing of multiple tracepoint events in the same -e 
switch: https://lkml.org/lkml/2010/11/30/460

When I dig into the code a bit, I find that each event opens 
successfully, so that's not the problem.  If I disable the grouping, 
then I get counts for all of the tracepoint events.

- Corey

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