linux-kernel - Re: [PATCH] perf_counter: Start counting time enabled when group leader gets enabled

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Message-Id: <1251184888.7538.1087.camel@twins>
Date:	Tue, 25 Aug 2009 09:21:28 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Paul Mackerras <paulus@...ba.org>
Cc:	eranian@...il.com, Ingo Molnar <mingo@...e.hu>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Robert Richter <robert.richter@....com>,
	Andi Kleen <andi@...stfloor.org>,
	Maynard Johnson <mpjohn@...ibm.com>,
	Carl Love <cel@...ibm.com>,
	Corey J Ashford <cjashfor@...ibm.com>,
	Philip Mucci <mucci@...s.utk.edu>,
	Dan Terpstra <terpstra@...s.utk.edu>,
	perfmon2-devel <perfmon2-devel@...ts.sourceforge.net>
Subject: Re: [PATCH] perf_counter: Start counting time enabled when group
 leader gets enabled

On Tue, 2009-08-25 at 15:17 +1000, Paul Mackerras wrote:
> Currently, if a group is created where the group leader is initially
> disabled but a non-leader member is initially enabled, and then the
> leader is subsequently enabled some time later, the time_enabled for
> the non-leader member will reflect the whole time since it was created,
> not just the time since the leader was enabled.  This is incorrect,
> because all of the members are effectively disabled while the leader
> is disabled, since none of the members can go on the PMU if the leader
> can't.
> 
> Thus we have to update the ->tstamp_enabled for all the enabled group
> members when a group leader is enabled, so that the time_enabled
> computation only counts the time since the leader was enabled.
> Similarly, when disabling a group leader we have to update the
> time_enabled and time_running for all of the group members.
> Also, in update_counter_times, we have to treat a counter whose group
> leader is disabled as being disabled.
> 
> Reported-by: Stephane Eranian <eranian@...glemail.com>
> Signed-off-by: Paul Mackerras <paulus@...ba.org>

Looks good, thanks Paul!

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