[PATCH] perf tools: Add comment for idx in struct perf_sample_id

[Adrian Hunter]

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

Signed-off-by: Adrian Hunter <adrian.hunter@xxxxxxxxx>
---
 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 cad54e8ba522..ba13eb771775 100644
--- a/tools/perf/util/evsel.h
+++ b/tools/perf/util/evsel.h
@@ -22,6 +22,13 @@ struct perf_sample_id {
 	struct hlist_node 	node;
 	u64		 	id;
 	struct perf_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;
-- 
2.17.1