Re: [PATCH 1/2] perf: Reset detached siblings' group_flags

Peter Zijlstra
2013-03-11T10:00:00Z

On Thu, 2013-03-07 at 13:19 +0900, Namhyung Kim wrote:
> From: Namhyung Kim <namhyung.kim@lge.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@redhat.com>
> Cc: Frederic Weisbecker <fweisbec@gmail.com>
> Signed-off-by: Namhyung Kim <namhyung@kernel.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.