From f38628b06c36222367e26820879789ae59e49f60 Mon Sep 17 00:00:00 2001 From: Namhyung Kim Date: Tue, 6 Feb 2024 21:05:45 -0800 Subject: [PATCH] perf/core: Reduce PMU access to adjust sample freq In perf_adjust_freq_unthr_context(), it first starts the event and then stop unnecessarily to adjust the sampling frequency if the event is throttled. For a throttled non-frequency event, it doesn't have a freq so no need to adjust. Just starting the event would be ok. For a frequency event, whether it's throttled or not, it needs to stop before adjusting the frequency. That means it should not start the even if it was throttled. I tried to skip calling the stop callback, but it didn't work well since the event count might not be up to date. It should call the stop callback with PERF_EF_UPDATE anyway. However not calling start would prevent unnecessary MSR accesses (which can be costly) for already stopped events as stop state is saved in the hw config. Signed-off-by: Namhyung Kim Signed-off-by: Ingo Molnar Reviewed-by: Ian Rogers Reviewed-by: Kan Liang Link: https://lore.kernel.org/r/20240207050545.2727923-2-namhyung@kernel.org --- kernel/events/core.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/kernel/events/core.c b/kernel/events/core.c index 9566cfb273551..fd94e45a9d869 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -4146,7 +4146,8 @@ 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) + event->pmu->start(event, 0); } if (!event->attr.freq || !event->attr.sample_freq) -- 2.30.2