Messages in this thread | | | Date | Mon, 7 Jun 2021 17:27:25 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH v2 1/8] perf/ring_buffer: Add comment for barriers on AUX ring buffer |
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On Wed, Jun 02, 2021 at 06:30:00PM +0800, Leo Yan wrote: > AUX ring buffer applies almost the same barriers as perf ring buffer, > but there has an exception for ordering between writing the AUX trace > data and updating user_page::aux_head. > > This patch adds comment for how to use the barriers on AUX ring buffer, > and gives comment to ask the drivers to flush the trace data into AUX > ring buffer prior to updating user_page::aux_head. > > Signed-off-by: Leo Yan <leo.yan@linaro.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> --- > kernel/events/ring_buffer.c | 9 +++++++++ > 1 file changed, 9 insertions(+) > > diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c > index 52868716ec35..5cf6579be05e 100644 > --- a/kernel/events/ring_buffer.c > +++ b/kernel/events/ring_buffer.c > @@ -509,6 +509,15 @@ void perf_aux_output_end(struct perf_output_handle *handle, unsigned long size) > perf_event_aux_event(handle->event, aux_head, size, > handle->aux_flags); > > + /* > + * See perf_output_put_handle(), AUX ring buffer applies the same > + * barrier pairing as the perf ring buffer; except for B, since > + * AUX ring buffer is written by hardware trace, we cannot simply > + * use the generic memory barrier (like smp_wmb()) prior to update > + * user_page::aux_head, the hardware trace driver takes the > + * responsibility to ensure the trace data has been flushed into > + * the AUX buffer before calling perf_aux_output_end(). > + */ > WRITE_ONCE(rb->user_page->aux_head, rb->aux_head); > if (rb_need_aux_wakeup(rb)) > wakeup = true; > -- > 2.25.1 >
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