perf: Add API for PMUs to write to the AUX area

For pmus that wish to write data to ring buffer's AUX area, provide
perf_aux_output_{begin,end}() calls to initiate/commit data writes,
similarly to perf_output_{begin,end}. These also use the same output
handle structure. Also, similarly to software counterparts, these
will direct inherited events' output to parents' ring buffers.

After the perf_aux_output_begin() returns successfully, handle->size
is set to the maximum amount of data that can be written wrt aux_tail
pointer, so that no data that the user hasn't seen will be overwritten,
therefore this should always be called before hardware writing is
enabled. On success, this will return the pointer to pmu driver's
private structure allocated for this aux area by pmu::setup_aux. Same
pointer can also be retrieved using perf_get_aux() while hardware
writing is enabled.

PMU driver should pass the actual amount of data written as a parameter
to perf_aux_output_end(). All hardware writes should be completed and
visible before this one is called.

Additionally, perf_aux_output_skip() will adjust output handle and
aux_head in case some part of the buffer has to be skipped over to
maintain hardware's alignment constraints.

Nested writers are forbidden and guards are in place to catch such
attempts.

Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Kaixu Xia <kaixu.xia@linaro.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Robert Richter <rric@kernel.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: acme@infradead.org
Cc: adrian.hunter@intel.com
Cc: kan.liang@intel.com
Cc: markus.t.metzger@intel.com
Cc: mathieu.poirier@linaro.org
Link: http://lkml.kernel.org/r/1421237903-181015-8-git-send-email-alexander.shishkin@linux.intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 23 insertions, 1 deletions

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index f936a1e51f29..45c5873ad9b3 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -573,7 +573,10 @@ struct perf_output_handle {
 	struct ring_buffer		*rb;
 	unsigned long			wakeup;
 	unsigned long			size;
-	void				*addr;
+	union {
+		void			*addr;
+		unsigned long		head;
+	};
 	int				page;
 };
 
@@ -608,6 +611,14 @@ perf_cgroup_from_task(struct task_struct *task)
 
 #ifdef CONFIG_PERF_EVENTS
 
+extern void *perf_aux_output_begin(struct perf_output_handle *handle,
+				   struct perf_event *event);
+extern void perf_aux_output_end(struct perf_output_handle *handle,
+				unsigned long size, bool truncated);
+extern int perf_aux_output_skip(struct perf_output_handle *handle,
+				unsigned long size);
+extern void *perf_get_aux(struct perf_output_handle *handle);
+
 extern int perf_pmu_register(struct pmu *pmu, const char *name, int type);
 extern void perf_pmu_unregister(struct pmu *pmu);
 
@@ -898,6 +909,17 @@ extern void perf_event_disable(struct perf_event *event);
 extern int __perf_event_disable(void *info);
 extern void perf_event_task_tick(void);
 #else /* !CONFIG_PERF_EVENTS: */
+static inline void *
+perf_aux_output_begin(struct perf_output_handle *handle,
+		      struct perf_event *event)				{ return NULL; }
+static inline void
+perf_aux_output_end(struct perf_output_handle *handle, unsigned long size,
+		    bool truncated)					{ }
+static inline int
+perf_aux_output_skip(struct perf_output_handle *handle,
+		     unsigned long size)				{ return -EINVAL; }
+static inline void *
+perf_get_aux(struct perf_output_handle *handle)				{ return NULL; }
 static inline void
 perf_event_task_sched_in(struct task_struct *prev,
 			 struct task_struct *task)			{ }