Re: [PATCH v2] perf tools: Ensure event leader stays at head of evlist after sorting

[Chun-Tse Shao]

My apologies, resend the patch:
lore.kernel.org/20260505211924.1961056-2-ctshao@xxxxxxxxxx

On Sun, May 3, 2026 at 6:51 PM Namhyung Kim <namhyung@xxxxxxxxxx> wrote:
>
> On Fri, May 01, 2026 at 03:33:47PM -0700, Chun-Tse Shao wrote:
> > From: Ian Rogers <irogers@xxxxxxxxxx>
> >
> > For evlist of a certain event/metric, the HEAD should be the event
> > leader. In some scenarios where uncore_xxx_0 does not exist, the event
> > leader is not the first element after sorting. For example, on my test
> > machine uncore_iio_0 does not exist, the event leader is uncore_iio_2.
> >
> > However, in `evlist__cmp`, it was reordered based on the PMU name, which
> > makes uncore_iio_1 the HEAD of evlist, breaking the following merge
> > logic in `evsel__merge_aliases`.
> >
> > The patch adds a loop at the end of
> > `parse_events__sort_events_and_fix_groups` to make sure the first
> > wildcard match is the earliest entry in the list, updating pointers
> > accordingly without breaking reordering detection.
> >
> > Tested on device lacks uncore_iio_0, and `perf test` looks good.
> >
> > Signed-off-by: Ian Rogers <irogers@xxxxxxxxxx>
> > Signed-off-by: Chun-Tse Shao <ctshao@xxxxxxxxxx>
> > ---
> > v2:
> >   Adding missing Signed-off-by from Ian Rogers.
> >   Renaming variable `l` to `orig_leader`.
>
> I can't see this.
>
> Thanks,
> Namhyung
>
> >
> > v1: lore.kernel.org/20260501043532.790711-1-ctshao@xxxxxxxxxx
> >
> >  tools/perf/util/parse-events.c | 27 +++++++++++++++++++++++++++
> >  1 file changed, 27 insertions(+)
> >
> > diff --git a/tools/perf/util/parse-events.c b/tools/perf/util/parse-events.c
> > index 1497e1f2a08c..be825617321d 100644
> > --- a/tools/perf/util/parse-events.c
> > +++ b/tools/perf/util/parse-events.c
> > @@ -2251,6 +2251,33 @@ static int parse_events__sort_events_and_fix_groups(struct list_head *list)
> >               }
> >               last_event_was_forced_leader = (force_grouped_leader == pos);
> >       }
> > +
> > +     /*
> > +      * Make sure the first wildcard match is the earliest entry in the list.
> > +      * Since list_sort might have reordered the aliases, the original leader
> > +      * might not be at the head of the list anymore. We find the first
> > +      * alias in the sorted list and make it the new leader, and redirect
> > +      * all other aliases to it.
> > +      */
> > +     list_for_each_entry(pos, list, core.node) {
> > +             struct evsel *l = pos->first_wildcard_match;
> > +
> > +             if (!l)
> > +                     continue;
> > +
> > +             if (l->first_wildcard_match) {
> > +                     /* Original leader was redirected to a new leader */
> > +                     pos->first_wildcard_match = l->first_wildcard_match;
> > +             } else if (pos->core.idx < l->core.idx) {
> > +                     /*
> > +                      * We are earlier than the original leader in sorted order,
> > +                      * and no earlier alias has claimed leadership yet.
> > +                      */
> > +                     l->first_wildcard_match = pos;
> > +                     pos->first_wildcard_match = NULL;
> > +             }
> > +     }
> > +
> >       list_for_each_entry(pos, list, core.node) {
> >               struct evsel *pos_leader = evsel__leader(pos);
> >
> > --
> > 2.54.0.545.g6539524ca2-goog
> >