perf tools: Only override the default :tid comm entry

Events may still be ordered even if there are no timestamps e.g. if the
data is recorded per-thread.

Also synthesized COMM events have a timestamp of zero.

Consequently it is better to keep comm entries even if they have a
timestamp of zero.

However, when a struct thread is created the command string is not known
and a comm entry with a string of the form ":<tid>" is used.

In that case thread->comm_set is false and the comm entry should be
overridden.
Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@gmail.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/r/1415715423-15563-4-git-send-email-adrian.hunter@intel.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/thread.c

@@ -103,15 +103,14 @@ struct comm *thread__exec_comm(const struct thread *thread)
 	return last;
 }
 
-/* CHECKME: time should always be 0 if event aren't ordered */
 int __thread__set_comm(struct thread *thread, const char *str, u64 timestamp,
 		       bool exec)
 {
 	struct comm *new, *curr = thread__comm(thread);
 	int err;
 
-	/* Override latest entry if it had no specific time coverage */
-	if (!curr->start && !curr->exec) {
+	/* Override the default :tid entry */
+	if (!thread->comm_set) {
 		err = comm__override(curr, str, timestamp, exec);
 		if (err)
 			return err;