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 ... :/
