linux-kernel - [PATCH v2 2/2] perf/core: Reduce PMU access to adjust sample freq

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Date: Thu, 11 Jan 2024 12:43:48 -0800
From: namhyung@...nel.org
To: Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>
Cc: Mark Rutland <mark.rutland@....com>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Mingwei Zhang <mizhang@...gle.com>,
	Namhyung Kim <namhyung@...nel.org>,
	Ian Rogers <irogers@...gle.com>,
	Kan Liang <kan.liang@...ux.intel.com>
Subject: [PATCH v2 2/2] perf/core: Reduce PMU access to adjust sample freq

From: Namhyung Kim <namhyung@...nel.org>

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.

Reviewed-by: Ian Rogers <irogers@...gle.com>
Reviewed-by: Kan Liang <kan.liang@...ux.intel.com>
Signed-off-by: Namhyung Kim <namhyung@...nel.org>
---
 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 e9ce79c8c145..243cd09ba7fe 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -4121,10 +4121,15 @@ 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;
 
 		/*
@@ -4132,6 +4137,7 @@ 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;
@@ -4146,6 +4152,7 @@ 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);
 	}
 }
-- 
2.43.0.275.g3460e3d667-goog