[PATCH 18/19] perf tools: Store PERF_RECORD_FINISHED_ROUND only for nonempty rounds

[Jiri Olsa]

Currently we store PERF_RECORD_FINISHED_ROUND event each time
we go throught mmap buffers no matter if it contains any data,
which is useless.

Forcing the PERF_RECORD_FINISHED_ROUND event to be stored any
time we finished the round AND wrote at least one event.

Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Cc: Corey Ashford <cjashfor@xxxxxxxxxxxxxxxxxx>
Cc: David Ahern <dsahern@xxxxxxxxx>
Cc: Frederic Weisbecker <fweisbec@xxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Jean Pihet <jean.pihet@xxxxxxxxxx>
Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
Cc: Paul Mackerras <paulus@xxxxxxxxx>
Cc: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>
---
 tools/perf/builtin-record.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
index 4a1a54265b04..4869050e7194 100644
--- a/tools/perf/builtin-record.c
+++ b/tools/perf/builtin-record.c
@@ -238,6 +238,7 @@ static struct perf_event_header finished_round_event = {
 
 static int record__mmap_read_all(struct record *rec)
 {
+	u64 bytes_written = rec->bytes_written;
 	int i;
 	int rc = 0;
 
@@ -250,7 +251,12 @@ static int record__mmap_read_all(struct record *rec)
 		}
 	}
 
-	rc = record__write(rec, &finished_round_event, sizeof(finished_round_event));
+	/*
+	 * Mark the round finished in case we wrote
+	 * at least one event.
+	 */
+	if (bytes_written != rec->bytes_written)
+		rc = record__write(rec, &finished_round_event, sizeof(finished_round_event));
 
 out:
 	return rc;
-- 
1.8.3.1

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