Measure processing latency

hw/buffer.h

@@ -17,6 +17,7 @@ typedef struct buffer_s {
   int mmap_reflinks;
   struct buffer_s *mmap_source;
   bool enqueued;
+  uint64_t enqueue_time_us;
 } buffer_t;
 
 buffer_t *buffer_open(const char *name, struct buffer_list_s *buf_list, int buffer);