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perf/ring_buffer: Document AUX API usage

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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 the perf_aux_output_{begin,end}()
APIs.

Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Arnaldo Carvalho de Melo <acme@infradead.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mathieu Poirier <mathieu.poirier@linaro.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Cc: vince@deater.net
Link: http://lkml.kernel.org/r/1457098969-21595-4-git-send-email-alexander.shishkin@linux.intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Alexander Shishkin 2016-03-04 15:42:47 +02:00 committed by Ingo Molnar
parent 95ff4ca26c
commit af5bb4ed12
1 changed files with 10 additions and 0 deletions
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10
kernel/events/ring_buffer.c
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@ -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 @@ void *perf_aux_output_begin(struct perf_output_handle *handle,
* 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);
}