diff options
| author | Alexander Shishkin <alexander.shishkin@linux.intel.com> | 2016-03-04 15:42:47 +0200 |
|---|---|---|
| committer | Mathieu Poirier <mathieu.poirier@linaro.org> | 2016-06-01 15:42:47 -0600 |
| commit | 84b84017f4369341bdf54054f86947043fa534ef (patch) | |
| tree | 1c544f9bc3ce8f837561f88661a6436357351fbe | |
| parent | c5611c7b5fc21996fc8d81e0d6cbcd75ced77bbb (diff) | |
perf/ring_buffer: Document AUX API usage
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>
(cherry picked from commit af5bb4ed1254a378b6028c09e58bdcc1cd9bf5b3)
| -rw-r--r-- | kernel/events/ring_buffer.c | 10 |
1 files changed, 10 insertions, 0 deletions
diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c index dcd21cae982c..084be7d41bcf 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) @@ -384,6 +393,7 @@ 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); } |