perf bench: Fix bench/sched-pipe.c to wait for child process

Ingo reported this small 'perf bench sched pipe' output problem:

 | $ ./perf bench sched pipe
 | (executing 1000000 pipe operations between two tasks)
 |
 |	Total time:4.898 sec
 | $		4.898586 usecs/op
 |		204140 ops/sec
 |
 | the shell prompt came back before the usecs/op and ops/sec line
 | was printed. Process teardown race, lack of wait() or so?

This caused by lack of calling waitpid() by parent process,
so I added it.

Signed-off-by: Hitoshi Mitake <mitake@dcl.info.waseda.ac.jp>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jiri Kosina <jkosina@suse.cz>
LKML-Reference: <1257737465-7546-1-git-send-email-mitake@dcl.info.waseda.ac.jp>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 7 insertions, 3 deletions

diff --git a/tools/perf/bench/sched-pipe.c b/tools/perf/bench/sched-pipe.c
index 3214ed20b1aa..6a29100e9282 100644
--- a/tools/perf/bench/sched-pipe.c
+++ b/tools/perf/bench/sched-pipe.c
@@ -26,6 +26,7 @@
 #include <errno.h>
 #include <assert.h>
 #include <sys/time.h>
+#include <sys/types.h>
 
 #define LOOPS_DEFAULT 1000000
 static int loops = LOOPS_DEFAULT;
@@ -58,8 +59,8 @@ int bench_sched_pipe(int argc, const char **argv,
          * discarding returned value of read(), write()
          * causes error in building environment for perf
          */
-        int ret;
-        pid_t pid;
+        int ret, wait_stat;
+        pid_t pid, retpid;
 
         argc = parse_options(argc, argv, options,
                              bench_sched_pipe_usage, 0);
@@ -87,8 +88,11 @@ int bench_sched_pipe(int argc, const char **argv,
         gettimeofday(&stop, NULL);
         timersub(&stop, &start, &diff);
 
-        if (pid)
+        if (pid) {
+                retpid = waitpid(pid, &wait_stat, 0);
+                assert((retpid == pid) && WIFEXITED(wait_stat));
                 return 0;
+        }
 
         if (simple)
                 printf("%lu.%03lu\n",