perf tools: Ensure event leader stays at head of evlist after sorting

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: Chun-Tse Shao <ctshao@google.com>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: James Clark <james.clark@linaro.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Falcon <thomas.falcon@intel.com>
Cc: Thomas Richter <tmricht@linux.ibm.com>
Signed-off-by: Ian Rogers <irogers@google.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

diff --git a/tools/perf/util/parse-events.c b/tools/perf/util/parse-events.c
index 1497e1f2a08ca633a30fc8a337c696e36ecfacfb..943569e82b82f91ab351e23f6c4ad853bf4d3cde 100644 (file)
--- 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 *orig_leader = pos->first_wildcard_match;
+
+               if (!orig_leader)
+                       continue;
+
+               if (orig_leader->first_wildcard_match) {
+                       /* Original leader was redirected to a new leader */
+                       pos->first_wildcard_match = orig_leader->first_wildcard_match;
+               } else if (pos->core.idx < orig_leader->core.idx) {
+                       /*
+                        * We are earlier than the original leader in sorted order,
+                        * and no earlier alias has claimed leadership yet.
+                        */
+                       orig_leader->first_wildcard_match = pos;
+                       pos->first_wildcard_match = NULL;
+               }
+       }
+
        list_for_each_entry(pos, list, core.node) {
                struct evsel *pos_leader = evsel__leader(pos);