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-rw-r--r--tools/perf/util/cs-etm-decoder/cs-etm-decoder.c12
1 files changed, 10 insertions, 2 deletions
diff --git a/tools/perf/util/cs-etm-decoder/cs-etm-decoder.c b/tools/perf/util/cs-etm-decoder/cs-etm-decoder.c
index c8b98fa22997..4d5fc374e730 100644
--- a/tools/perf/util/cs-etm-decoder/cs-etm-decoder.c
+++ b/tools/perf/util/cs-etm-decoder/cs-etm-decoder.c
@@ -96,11 +96,19 @@ int cs_etm_decoder__get_packet(struct cs_etm_decoder *decoder,
/* Nothing to do, might as well just return */
if (decoder->packet_count == 0)
return 0;
+ /*
+ * The queueing process in function cs_etm_decoder__buffer_packet()
+ * increments the tail *before* using it. This is somewhat counter
+ * intuitive but it has the advantage of centralizing tail management
+ * at a single location. Because of that we need to follow the same
+ * heuristic with the head, i.e we increment it before using its
+ * value. Otherwise the first element of the packet queue is not
+ * used.
+ */
+ decoder->head = (decoder->head + 1) & (MAX_BUFFER - 1);
*packet = decoder->packet_buffer[decoder->head];
- decoder->head = (decoder->head + 1) & (MAX_BUFFER - 1);
-
decoder->packet_count--;
return 1;