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

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Date:   Tue, 21 Nov 2023 10:57:54 -0500
From:   "Liang, Kan" <kan.liang@...ux.intel.com>
To:     Namhyung Kim <namhyung@...nel.org>,
        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>,
        Ian Rogers <irogers@...gle.com>,
        Mingwei Zhang <mizhang@...gle.com>
Subject: Re: [PATCH 2/3] perf/core: Reduce PMU access to adjust sample freq



On 2023-11-20 5:19 p.m., Namhyung Kim wrote:
> 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@...nel.org>

Reviewed-by: Kan Liang <kan.liang@...ux.intel.com>

Thanks,
Kan

> ---
>  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);
>  	}
>  }