Re: [PATCH 1/3] perf/core: Update perf_adjust_freq_unthr_context()

[Mingwei Zhang <mizhang@google.com>]

On Mon, Nov 20, 2023, Namhyung Kim wrote:
> It was unnecessarily disabling and enabling PMUs for each event.  It
> should be done at PMU level.  Add pmu_ctx->nr_freq counter to check it
> at each PMU.  As pmu context has separate active lists for pinned group
> and flexible group, factor out a new function to do the job.
> 
> Another minor optimization is that it can skip PMUs w/ CAP_NO_INTERRUPT
> even if it needs to unthrottle sampling events.
> 
> Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Tested-by: Mingwei Zhang <mizhang@google.com>
> ---
>  include/linux/perf_event.h |  1 +
>  kernel/events/core.c       | 68 +++++++++++++++++++++++---------------
>  2 files changed, 43 insertions(+), 26 deletions(-)
> 
> diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
> index 0367d748fae0..3eb17dc89f5e 100644
> --- a/include/linux/perf_event.h
> +++ b/include/linux/perf_event.h
> @@ -879,6 +879,7 @@ struct perf_event_pmu_context {
>  
>  	unsigned int			nr_events;
>  	unsigned int			nr_cgroups;
> +	unsigned int			nr_freq;
>  
>  	atomic_t			refcount; /* event <-> epc */
>  	struct rcu_head			rcu_head;
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 3eb26c2c6e65..53e2ad73102d 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -2275,8 +2275,10 @@ event_sched_out(struct perf_event *event, struct perf_event_context *ctx)
>  
>  	if (!is_software_event(event))
>  		cpc->active_oncpu--;
> -	if (event->attr.freq && event->attr.sample_freq)
> +	if (event->attr.freq && event->attr.sample_freq) {
>  		ctx->nr_freq--;
> +		epc->nr_freq--;
> +	}
>  	if (event->attr.exclusive || !cpc->active_oncpu)
>  		cpc->exclusive = 0;
>  
> @@ -2531,9 +2533,10 @@ event_sched_in(struct perf_event *event, struct perf_event_context *ctx)
>  
>  	if (!is_software_event(event))
>  		cpc->active_oncpu++;
> -	if (event->attr.freq && event->attr.sample_freq)
> +	if (event->attr.freq && event->attr.sample_freq) {
>  		ctx->nr_freq++;
> -
> +		epc->nr_freq++;
> +	}
>  	if (event->attr.exclusive)
>  		cpc->exclusive = 1;
>  
> @@ -4096,30 +4099,14 @@ static void perf_adjust_period(struct perf_event *event, u64 nsec, u64 count, bo
>  	}
>  }
>  
> -/*
> - * combine freq adjustment with unthrottling to avoid two passes over the
> - * events. At the same time, make sure, having freq events does not change
> - * the rate of unthrottling as that would introduce bias.
> - */
> -static void
> -perf_adjust_freq_unthr_context(struct perf_event_context *ctx, bool unthrottle)
> +static void perf_adjust_freq_unthr_events(struct list_head *event_list)
>  {
>  	struct perf_event *event;
>  	struct hw_perf_event *hwc;
>  	u64 now, period = TICK_NSEC;
>  	s64 delta;
>  
> -	/*
> -	 * only need to iterate over all events iff:
> -	 * - context have events in frequency mode (needs freq adjust)
> -	 * - there are events to unthrottle on this cpu
> -	 */
> -	if (!(ctx->nr_freq || unthrottle))
> -		return;
> -
> -	raw_spin_lock(&ctx->lock);
> -
> -	list_for_each_entry_rcu(event, &ctx->event_list, event_entry) {
> +	list_for_each_entry(event, event_list, active_list) {
>  		if (event->state != PERF_EVENT_STATE_ACTIVE)
>  			continue;
>  
> @@ -4127,8 +4114,6 @@ perf_adjust_freq_unthr_context(struct perf_event_context *ctx, bool unthrottle)
>  		if (!event_filter_match(event))
>  			continue;
>  
> -		perf_pmu_disable(event->pmu);
> -
>  		hwc = &event->hw;
>  
>  		if (hwc->interrupts == MAX_INTERRUPTS) {
> @@ -4138,7 +4123,7 @@ perf_adjust_freq_unthr_context(struct perf_event_context *ctx, bool unthrottle)
>  		}
>  
>  		if (!event->attr.freq || !event->attr.sample_freq)
> -			goto next;
> +			continue;
>  
>  		/*
>  		 * stop the event and update event->count
> @@ -4160,8 +4145,39 @@ perf_adjust_freq_unthr_context(struct perf_event_context *ctx, bool unthrottle)
>  			perf_adjust_period(event, period, delta, false);
>  
>  		event->pmu->start(event, delta > 0 ? PERF_EF_RELOAD : 0);
> -	next:
> -		perf_pmu_enable(event->pmu);
> +	}
> +}
> +
> +/*
> + * combine freq adjustment with unthrottling to avoid two passes over the
> + * events. At the same time, make sure, having freq events does not change
> + * the rate of unthrottling as that would introduce bias.
> + */
> +static void
> +perf_adjust_freq_unthr_context(struct perf_event_context *ctx, bool unthrottle)
> +{
> +	struct perf_event_pmu_context *pmu_ctx;
> +
> +	/*
> +	 * only need to iterate over all events iff:
> +	 * - context have events in frequency mode (needs freq adjust)
> +	 * - there are events to unthrottle on this cpu
> +	 */
> +	if (!(ctx->nr_freq || unthrottle))
> +		return;
> +
> +	raw_spin_lock(&ctx->lock);
> +
> +	list_for_each_entry(pmu_ctx, &ctx->pmu_ctx_list, pmu_ctx_entry) {
> +		if (!(pmu_ctx->nr_freq || unthrottle))
> +			continue;
> +		if (pmu_ctx->pmu->capabilities & PERF_PMU_CAP_NO_INTERRUPT)
> +			continue;
> +
> +		perf_pmu_disable(pmu_ctx->pmu);
> +		perf_adjust_freq_unthr_events(&pmu_ctx->pinned_active);
> +		perf_adjust_freq_unthr_events(&pmu_ctx->flexible_active);
> +		perf_pmu_enable(pmu_ctx->pmu);
>  	}
>  
>  	raw_spin_unlock(&ctx->lock);
> -- 
> 2.43.0.rc1.413.gea7ed67945-goog
>