Messages in this thread | | | Date | Fri, 4 Aug 2017 23:43:08 +0530 | From | "Naveen N. Rao" <> | Subject | Re: [PATCH v2 2/2] kernel/events: Add option to enable counting sideband events in wakeup_events |
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On 2017/08/04 12:59PM, Peter Zijlstra wrote: > On Tue, Aug 01, 2017 at 08:14:04PM +0530, Naveen N. Rao wrote: > > @@ -5974,19 +5976,8 @@ void perf_output_sample(struct perf_output_handle *handle, > > } > > } > > > > + if (!event->attr.count_sb_events) > > + rb_handle_wakeup_events(event, handle->rb); > > } > > > +void __always_inline > > +rb_handle_wakeup_events(struct perf_event *event, struct ring_buffer *rb) > > +{ > > + int wakeup_events = event->attr.wakeup_events; > > + > > + if (!event->attr.watermark && wakeup_events) { > > + int events = local_inc_return(&rb->events); > > + > > + if (events >= wakeup_events) { > > + local_sub(wakeup_events, &rb->events); > > + local_inc(&rb->wakeup); > > + } > > + } > > +} > > + > > static int __always_inline > > __perf_output_begin(struct perf_output_handle *handle, > > struct perf_event *event, unsigned int size, > > @@ -197,6 +212,9 @@ __perf_output_begin(struct perf_output_handle *handle, > > * none of the data stores below can be lifted up by the compiler. > > */ > > > > + if (unlikely(event->attr.count_sb_events)) > > + rb_handle_wakeup_events(event, rb); > > + > > if (unlikely(head - local_read(&rb->wakeup) > rb->watermark)) > > local_add(rb->watermark, &rb->wakeup); > > > > I'm still slightly uneasy over this.. Yes most of our events are > samples, so we'd pay the overhead already. But could you still look at > performance of this, see for example this commit: > > 9ecda41acb97 ("perf/core: Add ::write_backward attribute to perf event") > > we went through a lot of variants to not hurt performance.
Sure. I'll run the tests and get back.
Thanks, Naveen
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