linux-kernel - Re: [PATCH 1/2] perf: Reset detached siblings' group

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Date:	Mon, 11 Mar 2013 10:59:44 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Namhyung Kim <namhyung@...nel.org>
Cc:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Paul Mackerras <paulus@...ba.org>,
	Ingo Molnar <mingo@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Stephane Eranian <eranian@...gle.com>,
	Namhyung Kim <namhyung.kim@....com>,
	Jiri Olsa <jolsa@...hat.com>,
	Frederic Weisbecker <fweisbec@...il.com>
Subject: Re: [PATCH 1/2] perf: Reset detached siblings' group_flags

On Thu, 2013-03-07 at 13:19 +0900, Namhyung Kim wrote:
> From: Namhyung Kim <namhyung.kim@....com>
> 
> Currently if a group_leader event is deleted, the sibling events are
> upgraded to singleton events of a same group list.  At this time, the
> siblings inherit the leader's group_flags.
> 
> However, if the group has mixed hw/sw events the leader's group_flag
> does not contain PERF_GROUP_SOFTWARE so sibling sw events will miss
> the flag also.  Fix it.
> 
> Cc: Jiri Olsa <jolsa@...hat.com>
> Cc: Frederic Weisbecker <fweisbec@...il.com>
> Signed-off-by: Namhyung Kim <namhyung@...nel.org>
> ---
>  kernel/events/core.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 5c75791d7269..007dfe846d4d 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -1107,8 +1107,9 @@ static void perf_group_detach(struct perf_event *event)
>  			list_move_tail(&sibling->group_entry, list);
>  		sibling->group_leader = sibling;
>  
> -		/* Inherit group flags from the previous leader */
> -		sibling->group_flags = event->group_flags;
> +		/* Reset group flags for each siblings */
> +		sibling->group_flags = is_software_event(sibling) ?
> +						PERF_GROUP_SOFTWARE : 0;
>  	}


In such a case, does the event not continue to live on the hw pmu? That
is, after this patch we'll have a software event on the hardware pmu
list with PERF_GROUP_SOFTWARE set, right? Seems odd.

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