[tip: perf/core] perf evsel: Add comment for 'idx' member in 'struct perf_sample_id

[tip-bot2 for Adrian Hunter]

The following commit has been merged into the perf/core branch of tip:

Commit-ID:     3c84e65a533dbaa1a29bfd847deca73704b675eb
Gitweb:        https://git.kernel.org/tip/3c84e65a533dbaa1a29bfd847deca73704b675eb
Author:        Adrian Hunter <adrian.hunter@xxxxxxxxx>
AuthorDate:    Mon, 12 Aug 2019 12:09:35 +03:00
Committer:     Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
CommitterDate: Tue, 20 Aug 2019 12:17:45 -03:00

perf evsel: Add comment for 'idx' member in 'struct perf_sample_id

The 'idx' member was added as preparation for AUX area sampling. Add a
comment to describe why.

Signed-off-by: Adrian Hunter <adrian.hunter@xxxxxxxxx>
Cc: Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: Michael Petlan <mpetlan@xxxxxxxxxx>
Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/83ff264f-84c3-5372-8976-dd9293d20c6f@xxxxxxxxx
Signed-off-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
---
 tools/perf/util/evsel.h | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/tools/perf/util/evsel.h b/tools/perf/util/evsel.h
index 9cd6e3a..efe0806 100644
--- a/tools/perf/util/evsel.h
+++ b/tools/perf/util/evsel.h
@@ -23,6 +23,13 @@ struct perf_sample_id {
 	struct hlist_node 	node;
 	u64		 	id;
 	struct evsel		*evsel;
+       /*
+	* 'idx' will be used for AUX area sampling. A sample will have AUX area
+	* data that will be queued for decoding, where there are separate
+	* queues for each CPU (per-cpu tracing) or task (per-thread tracing).
+	* The sample ID can be used to lookup 'idx' which is effectively the
+	* queue number.
+	*/
 	int			idx;
 	int			cpu;
 	pid_t			tid;