[PATCH 2/3] perf/core: Reduce PMU access to adjust sample freq

[Namhyung Kim]

For throttled events, it first starts the event and then stop
unnecessarily.  As it's already stopped, it can directly adjust
the frequency and then move on.

Signed-off-by: Namhyung Kim <namhyung@xxxxxxxxxx>
---
 kernel/events/core.c | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 53e2ad73102d..fd3449e4d081 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -4119,10 +4119,15 @@ static void perf_adjust_freq_unthr_events(struct list_head *event_list)
 		if (hwc->interrupts == MAX_INTERRUPTS) {
 			hwc->interrupts = 0;
 			perf_log_throttle(event, 1);
-			event->pmu->start(event, 0);
-		}
 
-		if (!event->attr.freq || !event->attr.sample_freq)
+			if (!event->attr.freq || !event->attr.sample_freq) {
+				delta = 0;
+				goto next;
+			}
+
+			if (event->hw.state & PERF_HES_STOPPED)
+				goto adjust;
+		} else if (!event->attr.freq || !event->attr.sample_freq)
 			continue;
 
 		/*
@@ -4130,6 +4135,7 @@ static void perf_adjust_freq_unthr_events(struct list_head *event_list)
 		 */
 		event->pmu->stop(event, PERF_EF_UPDATE);
 
+adjust:
 		now = local64_read(&event->count);
 		delta = now - hwc->freq_count_stamp;
 		hwc->freq_count_stamp = now;
@@ -4144,6 +4150,7 @@ static void perf_adjust_freq_unthr_events(struct list_head *event_list)
 		if (delta > 0)
 			perf_adjust_period(event, period, delta, false);
 
+next:
 		event->pmu->start(event, delta > 0 ? PERF_EF_RELOAD : 0);
 	}
 }
-- 
2.43.0.rc1.413.gea7ed67945-goog