linux-kernel - [BUG] perf_event: when events are grouped, the time enabled / running values are incorrect

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Date:	Fri, 07 May 2010 18:56:15 -0700
From:	Corey Ashford <cjashfor@...ux.vnet.ibm.com>
To:	LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Paul Mackerras <paulus@...ba.org>
CC:	Stephane Eranian <eranian@...glemail.com>
Subject: [BUG] perf_event: when events are grouped, the time enabled / running
 values are incorrect

Hi,

There appears to be a bug in the kernel related to reading up the time 
running and enabled values for events that are in a group.  The group 
leader's time running and time enable values look correct, but all of 
the other group members have a zero value for their time running and 
time enabled fields.

This happens only when remote monitoring a process (perhaps only after 
it has terminated)... when self monitoring, the time running/enabled 
values come out non-zero, and the values are the same for all of the 
counters (as one would expect since they can be enabled/disabled 
simultaneously).

I've attached a test case which you can place in the tools/perf 
subdirectory and compile with just:

gcc -o show_re_bug show_re_bug.c

Thanks for your consideration,

- Corey

Corey Ashford
Software Engineer
IBM Linux Technology Center, Linux Toolchain
Beaverton, OR
cjashfor@...ibm.com

View attachment "show_re_bug.c" of type "text/plain" (6357 bytes)