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

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Message-ID: <4BEAE476.1090100@linux.vnet.ibm.com>
Date:	Wed, 12 May 2010 10:25:10 -0700
From:	Corey Ashford <cjashfor@...ux.vnet.ibm.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	LKML <linux-kernel@...r.kernel.org>,
	Paul Mackerras <paulus@...ba.org>,
	Stephane Eranian <eranian@...glemail.com>
Subject: Re: [BUG] perf_event: when events are grouped, the time enabled /
 running values are incorrect

On 05/11/2010 07:42 AM, Peter Zijlstra wrote:
> ---
> Subject: perf: Fix exit() vs event-groups
> From: Peter Zijlstra<a.p.zijlstra@...llo.nl>
> Date: Tue May 11 16:19:10 CEST 2010
>
> Corey reported that the value scale times of group siblings are not
> updated when the monitored task dies.
>
> The problem appears to be that we only update the group leader's
> time values, fix it by updating the whole group.
>
> Reported-by: Corey Ashford<cjashfor@...ux.vnet.ibm.com>
> Signed-off-by: Peter Zijlstra<a.p.zijlstra@...llo.nl>
> Cc: Paul Mackerras<paulus@...ba.org>
> Cc: stable@...nel.org
> ---
>   kernel/perf_event.c |   44 +++++++++++++++++++++++---------------------
>   1 file changed, 23 insertions(+), 21 deletions(-)
>
> Index: linux-2.6/kernel/perf_event.c
> ===================================================================
> --- linux-2.6.orig/kernel/perf_event.c
> +++ linux-2.6/kernel/perf_event.c
> @@ -255,6 +255,18 @@ static void update_event_times(struct pe
>   	event->total_time_running = run_end - event->tstamp_running;
>   }
>
> +/*
> + * Update total_time_enabled and total_time_running for all events in a group.
> + */
...

Peter,

Thanks for looking into this problem!  Unfortunately, I've been unable 
to test your patch.  It doesn't apply to 2.6.33.3 and so I tried the 
-tip tree (which has this patch committed).  The kernel built fine, but 
crashed almost immediately during the boot-up process on my Power5 machine.

I don't have the crash details at hand, but they didn't look related to 
this perf change.

- Corey
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