Messages in this thread | ![/](/images/icornerl.gif) | | Date | Thu, 13 Jul 2017 20:25:19 +0530 | From | "Naveen N. Rao" <> | Subject | Re: [PATCH 2/2] kernel/events: Add option to enable counting sideband events in wakeup_events |
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On 2017/07/12 01:48PM, Peter Zijlstra wrote: > On Mon, Jun 19, 2017 at 08:01:08PM +0530, Naveen N. Rao wrote: > > diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c > > index 4e7c728569a8..f43a6081141f 100644 > > --- a/kernel/events/ring_buffer.c > > +++ b/kernel/events/ring_buffer.c > > @@ -197,6 +197,19 @@ __perf_output_begin(struct perf_output_handle *handle, > > * none of the data stores below can be lifted up by the compiler. > > */ > > > > + if (event->attr.count_sb_events && !event->attr.watermark) { > > + int wakeup_events = event->attr.wakeup_events; > > + > > + if (wakeup_events) { > > + int events = local_inc_return(&rb->events); > > + > > + if (events >= wakeup_events) { > > + local_sub(wakeup_events, &rb->events); > > + local_inc(&rb->wakeup); > > + } > > + } > > + } > > + > > if (unlikely(head - local_read(&rb->wakeup) > rb->watermark)) > > local_add(rb->watermark, &rb->wakeup); > > > > So this is a very performance sensitive function; not at all happy to > add bits here ... :/
:O
Does it at all help if the above is instead guarded by: if (unlikely(event->attr.count_sb_events)) { ... }
That should hopefully limit the impact to only when that option is used?
Thanks, Naveen
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