From: Alexander Shishkin <alexander.shishkin@linux.intel.com>
To: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Ingo Molnar <mingo@redhat.com>,
linux-kernel@vger.kernel.org, vince@deater.net,
eranian@google.com, Arnaldo Carvalho de Melo <acme@infradead.org>,
Alexander Shishkin <alexander.shishkin@linux.intel.com>,
Mathieu Poirier <mathieu.poirier@linaro.org>
Subject: [PATCH v2 3/5] perf: Document aux api usage
Date: Fri, 4 Mar 2016 15:42:47 +0200 [thread overview]
Message-ID: <1457098969-21595-4-git-send-email-alexander.shishkin@linux.intel.com> (raw)
In-Reply-To: <1457098969-21595-1-git-send-email-alexander.shishkin@linux.intel.com>
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 fb7f5bce27..b5feb7ebb9 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);
}
--
2.7.0
next prev parent reply other threads:[~2016-03-04 13:43 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-03-04 13:42 [PATCH v2 0/5] perf: Untangle aux refcounting Alexander Shishkin
2016-03-04 13:42 ` [PATCH v2 1/5] perf: Refuse to begin aux transaction after aux_mmap_count drops Alexander Shishkin
2016-03-31 9:23 ` [tip:perf/core] perf/ring_buffer: Refuse to begin AUX transaction after rb->aux_mmap_count drops tip-bot for Alexander Shishkin
2016-03-04 13:42 ` [PATCH v2 2/5] perf: Free aux pages in unmap path Alexander Shishkin
2016-03-14 12:38 ` Peter Zijlstra
2016-03-14 14:04 ` Alexander Shishkin
2016-03-14 16:42 ` Peter Zijlstra
2016-03-17 13:05 ` Alexander Shishkin
2016-03-23 8:34 ` Peter Zijlstra
2016-03-31 9:24 ` [tip:perf/core] perf/core: Free AUX " tip-bot for Alexander Shishkin
2016-03-04 13:42 ` Alexander Shishkin [this message]
2016-03-31 9:24 ` [tip:perf/core] perf/ring_buffer: Document AUX API usage tip-bot for Alexander Shishkin
2016-03-04 13:42 ` [PATCH v2 4/5] perf/x86/intel/pt: Move transaction start/stop to pmu start/stop callbacks Alexander Shishkin
2016-03-31 9:24 ` [tip:perf/core] perf/x86/intel/pt: Move transaction start/stop to PMU " tip-bot for Alexander Shishkin
2016-03-04 13:42 ` [PATCH v2 5/5] perf/x86/intel/bts: Move transaction start/stop to " Alexander Shishkin
2016-03-31 9:25 ` [tip:perf/core] " tip-bot for Alexander Shishkin
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