perf: Only dump the throttle log for the leader

The PERF_RECORD_THROTTLE records are dumped for all throttled events.
It's not necessary for group events, which are throttled altogether.

Optimize it by only dump the throttle log for the leader.

The sample right after the THROTTLE record must be generated by the
actual target event. It is good enough for the perf tool to locate the
actual target event.

Suggested-by: Namhyung Kim <[email protected]>
Signed-off-by: Kan Liang <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Acked-by: Namhyung Kim <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

Author: Kan Liang

kernel/events/core.c

@@ -2650,14 +2650,16 @@ static void perf_event_unthrottle(struct perf_event *event, bool start)
 	event->hw.interrupts = 0;
 	if (start)
 		event->pmu->start(event, 0);
-	perf_log_throttle(event, 1);
+	if (event == event->group_leader)
+		perf_log_throttle(event, 1);
 }
 
 static void perf_event_throttle(struct perf_event *event)
 {
 	event->pmu->stop(event, 0);
 	event->hw.interrupts = MAX_INTERRUPTS;
-	perf_log_throttle(event, 0);
+	if (event == event->group_leader)
+		perf_log_throttle(event, 0);
 }
 
 static void perf_event_unthrottle_group(struct perf_event *event, bool skip_start_event)