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;