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

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Date: Tue,  9 Jan 2024 13:36:23 -0800
From: Namhyung Kim <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>,
	Ian Rogers <irogers@...gle.com>,
	Kan Liang <kan.liang@...ux.intel.com>
Subject: [PATCH RESEND 2/2] perf/core: Reduce PMU access to adjust sample freq

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 ce9db9dbfd4c..c80b6aa0e354 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);
 	}
 }
-- 
2.43.0.472.g3155946c3a-goog