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

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Date:	Mon, 11 Mar 2013 20:34:21 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
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 Mon, 11 Mar 2013 10:59:44 +0100, Peter Zijlstra wrote:
> 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.

Right.

Just curious that dropping this one and applying just patch 2 will set
the PERF_GROUP_MIXED for them and it'll fix the mixed group problem
without migrating those events.  What do you think about this approach?

Thanks,
Namhyung
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