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SubjectRe: [PATCH 5/7] perf: Document aux api usage
From
On 3 December 2015 at 03:32, Alexander Shishkin
<alexander.shishkin@linux.intel.com> wrote:
> In order to ensure safe aux buffer management, we rely on the assumption
> that pmu::stop() stops its ongoing aux transaction and not just the hw.
>
> This patch documents this requirement for perf_aux_output_{begin,end}()
> apis.
>
> Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
> Cc: Mathieu Poirier <mathieu.poirier@linaro.org>
> ---
> kernel/events/ring_buffer.c | 10 ++++++++++
> 1 file changed, 10 insertions(+)
>
> diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c
> index 6865ac95ca..1aed2617e8 100644
> --- a/kernel/events/ring_buffer.c
> +++ b/kernel/events/ring_buffer.c
> @@ -252,6 +252,10 @@ ring_buffer_init(struct ring_buffer *rb, long watermark, int flags)
> * The ordering is similar to that of perf_output_{begin,end}, with
> * the exception of (B), which should be taken care of by the pmu
> * driver, since ordering rules will differ depending on hardware.
> + *
> + * Call this from pmu::start(); see the comment in perf_aux_output_end()
> + * about its use in pmu callbacks. Both can also be called from the PMI
> + * handler if needed.
> */
> void *perf_aux_output_begin(struct perf_output_handle *handle,
> struct perf_event *event)
> @@ -323,6 +327,7 @@ void *perf_aux_output_begin(struct perf_output_handle *handle,
> return handle->rb->aux_priv;
>
> err_put:
> + /* can't be last */
> rb_free_aux(rb);
>
> err:
> @@ -337,6 +342,10 @@ err:
> * aux_head and posting a PERF_RECORD_AUX into the perf buffer. It is the
> * pmu driver's responsibility to observe ordering rules of the hardware,
> * so that all the data is externally visible before this is called.
> + *
> + * Note: this has to be called from pmu::stop() callback, as the assumption
> + * of the aux buffer management code is that after pmu::stop(), the aux
> + * transaction must be stopped and therefore drop the aux reference count.
> */
> void perf_aux_output_end(struct perf_output_handle *handle, unsigned long size,
> bool truncated)
> @@ -376,6 +385,7 @@ void perf_aux_output_end(struct perf_output_handle *handle, unsigned long size,
> handle->event = NULL;
>
> local_set(&rb->aux_nest, 0);
> + /* can't be last */
> rb_free_aux(rb);
> ring_buffer_put(rb);
> }
> --
> 2.6.2
>

Thanks for the heads-up. My next version (V7) will follow the same scheme.

Mathieu


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