Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
 kernel/events/core.c |   51 +++++++++++++++++++++++----------------------------
 1 file changed, 23 insertions(+), 28 deletions(-)

--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -4090,7 +4090,7 @@ perf_adjust_freq_unthr_context(struct pe
 	if (!(ctx->nr_freq || unthrottle))
 		return;
 
-	raw_spin_lock(&ctx->lock);
+	guard(raw_spinlock)(&ctx->lock);
 
 	list_for_each_entry_rcu(event, &ctx->event_list, event_entry) {
 		if (event->state != PERF_EVENT_STATE_ACTIVE)
@@ -4100,7 +4100,7 @@ perf_adjust_freq_unthr_context(struct pe
 		if (!event_filter_match(event))
 			continue;
 
-		perf_pmu_disable(event->pmu);
+		guard(perf_pmu_disable)(event->pmu);
 
 		hwc = &event->hw;
 
@@ -4110,34 +4110,29 @@ perf_adjust_freq_unthr_context(struct pe
 			event->pmu->start(event, 0);
 		}
 
-		if (!event->attr.freq || !event->attr.sample_freq)
-			goto next;
+		if (event->attr.freq && event->attr.sample_freq) {
+			/*
+			 * stop the event and update event->count
+			 */
+			event->pmu->stop(event, PERF_EF_UPDATE);
+
+			now = local64_read(&event->count);
+			delta = now - hwc->freq_count_stamp;
+			hwc->freq_count_stamp = now;
+
+			/*
+			 * restart the event
+			 * reload only if value has changed
+			 * we have stopped the event so tell that
+			 * to perf_adjust_period() to avoid stopping it
+			 * twice.
+			 */
+			if (delta > 0)
+				perf_adjust_period(event, period, delta, false);
 
-		/*
-		 * stop the event and update event->count
-		 */
-		event->pmu->stop(event, PERF_EF_UPDATE);
-
-		now = local64_read(&event->count);
-		delta = now - hwc->freq_count_stamp;
-		hwc->freq_count_stamp = now;
-
-		/*
-		 * restart the event
-		 * reload only if value has changed
-		 * we have stopped the event so tell that
-		 * to perf_adjust_period() to avoid stopping it
-		 * twice.
-		 */
-		if (delta > 0)
-			perf_adjust_period(event, period, delta, false);
-
-		event->pmu->start(event, delta > 0 ? PERF_EF_RELOAD : 0);
-	next:
-		perf_pmu_enable(event->pmu);
+			event->pmu->start(event, delta > 0 ? PERF_EF_RELOAD : 0);
+		}
 	}
-
-	raw_spin_unlock(&ctx->lock);
 }
 
 /*

On Thu, Nov 2, 2023 at 8:32 AM Peter Zijlstra <peterz@infradead.org> wrote:
>
>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> ---
>  kernel/events/core.c |   51 +++++++++++++++++++++++----------------------------
>  1 file changed, 23 insertions(+), 28 deletions(-)
>
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -4090,7 +4090,7 @@ perf_adjust_freq_unthr_context(struct pe
>         if (!(ctx->nr_freq || unthrottle))
>                 return;
>
> -       raw_spin_lock(&ctx->lock);
> +       guard(raw_spinlock)(&ctx->lock);
>
>         list_for_each_entry_rcu(event, &ctx->event_list, event_entry) {
>                 if (event->state != PERF_EVENT_STATE_ACTIVE)
> @@ -4100,7 +4100,7 @@ perf_adjust_freq_unthr_context(struct pe
>                 if (!event_filter_match(event))
>                         continue;
>
> -               perf_pmu_disable(event->pmu);
> +               guard(perf_pmu_disable)(event->pmu);
>
>                 hwc = &event->hw;
>
> @@ -4110,34 +4110,29 @@ perf_adjust_freq_unthr_context(struct pe
>                         event->pmu->start(event, 0);
>                 }
>
> -               if (!event->attr.freq || !event->attr.sample_freq)
> -                       goto next;
> +               if (event->attr.freq && event->attr.sample_freq) {

Any reason for this change?  I think we can just change the
'goto next' to 'continue', no?

Also I think this code needs changes to optimize the access.
A similar reason for the cgroup switch, it accesses all the
pmu/events in the context even before checking the sampling
frequency.  This is bad for uncore PMUs (and KVM too).

But this is a different issue..

Thanks,
Namhyung


> +                       /*
> +                        * stop the event and update event->count
> +                        */
> +                       event->pmu->stop(event, PERF_EF_UPDATE);
> +
> +                       now = local64_read(&event->count);
> +                       delta = now - hwc->freq_count_stamp;
> +                       hwc->freq_count_stamp = now;
> +
> +                       /*
> +                        * restart the event
> +                        * reload only if value has changed
> +                        * we have stopped the event so tell that
> +                        * to perf_adjust_period() to avoid stopping it
> +                        * twice.
> +                        */
> +                       if (delta > 0)
> +                               perf_adjust_period(event, period, delta, false);
>
> -               /*
> -                * stop the event and update event->count
> -                */
> -               event->pmu->stop(event, PERF_EF_UPDATE);
> -
> -               now = local64_read(&event->count);
> -               delta = now - hwc->freq_count_stamp;
> -               hwc->freq_count_stamp = now;
> -
> -               /*
> -                * restart the event
> -                * reload only if value has changed
> -                * we have stopped the event so tell that
> -                * to perf_adjust_period() to avoid stopping it
> -                * twice.
> -                */
> -               if (delta > 0)
> -                       perf_adjust_period(event, period, delta, false);
> -
> -               event->pmu->start(event, delta > 0 ? PERF_EF_RELOAD : 0);
> -       next:
> -               perf_pmu_enable(event->pmu);
> +                       event->pmu->start(event, delta > 0 ? PERF_EF_RELOAD : 0);
> +               }
>         }
> -
> -       raw_spin_unlock(&ctx->lock);
>  }
>
>  /*
>
>

On Fri, Nov 03, 2023 at 06:14:32PM -0700, Namhyung Kim wrote:
> On Thu, Nov 2, 2023 at 8:32 AM Peter Zijlstra <peterz@infradead.org> wrote:
> >
> >
> > Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> > ---
> >  kernel/events/core.c |   51 +++++++++++++++++++++++----------------------------
> >  1 file changed, 23 insertions(+), 28 deletions(-)
> >
> > --- a/kernel/events/core.c
> > +++ b/kernel/events/core.c
> > @@ -4090,7 +4090,7 @@ perf_adjust_freq_unthr_context(struct pe
> >         if (!(ctx->nr_freq || unthrottle))
> >                 return;
> >
> > -       raw_spin_lock(&ctx->lock);
> > +       guard(raw_spinlock)(&ctx->lock);
> >
> >         list_for_each_entry_rcu(event, &ctx->event_list, event_entry) {
> >                 if (event->state != PERF_EVENT_STATE_ACTIVE)
> > @@ -4100,7 +4100,7 @@ perf_adjust_freq_unthr_context(struct pe
> >                 if (!event_filter_match(event))
> >                         continue;
> >
> > -               perf_pmu_disable(event->pmu);
> > +               guard(perf_pmu_disable)(event->pmu);
> >
> >                 hwc = &event->hw;
> >
> > @@ -4110,34 +4110,29 @@ perf_adjust_freq_unthr_context(struct pe
> >                         event->pmu->start(event, 0);
> >                 }
> >
> > -               if (!event->attr.freq || !event->attr.sample_freq)
> > -                       goto next;
> > +               if (event->attr.freq && event->attr.sample_freq) {
> 
> Any reason for this change?  I think we can just change the
> 'goto next' to 'continue', no?

Linus initially got confused about the life-time of for-loop scopes, but
yeah, this could be continue just fine.

> Also I think this code needs changes to optimize the access.
> A similar reason for the cgroup switch, it accesses all the
> pmu/events in the context even before checking the sampling
> frequency.  This is bad for uncore PMUs (and KVM too).
> 
> But this is a different issue..

Right, lets do that in another patch. Also, there seems to be a problem
with the cgroup thing :/