perf tools: Use machine->pid for tgid if machine is guest.

When we synthesize an comm event, if machine is guest, we should
use the pid of machine as the event->comm.pid, rather than tgid
of thread.
Signed-off-by: Dongsheng Yang <yangds.fnst@cn.fujitsu.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung.kim@lge.com>
Link: http://lkml.kernel.org/r/22455abe107c618a361e7b667ad0f098f7c9b4a3.1387572416.git.yangds.fnst@cn.fujitsu.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/event.c

@@ -106,8 +106,12 @@ static pid_t perf_event__synthesize_comm(struct perf_tool *tool,
 
 	memset(&event->comm, 0, sizeof(event->comm));
 
-	tgid = perf_event__get_comm_tgid(pid, event->comm.comm,
-					 sizeof(event->comm.comm));
+	if (machine__is_host(machine))
+		tgid = perf_event__get_comm_tgid(pid, event->comm.comm,
+						 sizeof(event->comm.comm));
+	else
+		tgid = machine->pid;
+
 	if (tgid < 0)
 		goto out;