Messages in this thread Patch in this message | | | Date | Wed, 10 Apr 2024 04:57:45 -0000 | From | "tip-bot2 for Namhyung Kim" <> | Subject | [tip: perf/core] perf/core: Reduce PMU access to adjust sample freq |
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The following commit has been merged into the perf/core branch of tip:
Commit-ID: f38628b06c36222367e26820879789ae59e49f60 Gitweb: https://git.kernel.org/tip/f38628b06c36222367e26820879789ae59e49f60 Author: Namhyung Kim <namhyung@kernel.org> AuthorDate: Tue, 06 Feb 2024 21:05:45 -08:00 Committer: Ingo Molnar <mingo@kernel.org> CommitterDate: Wed, 10 Apr 2024 06:13:57 +02:00
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 <namhyung@kernel.org> Signed-off-by: Ingo Molnar <mingo@kernel.org> Reviewed-by: Ian Rogers <irogers@google.com> Reviewed-by: Kan Liang <kan.liang@linux.intel.com> 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 9566cfb..fd94e45 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)
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