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Subject[PATCH] perf bench: Flush stdout before starting bench suite
From: Namhyung Kim <>

perf bench prints header message for bench suite before starting the
benchmark. However if the stdout is redirected to a file and bench
suite forks child processes this (and possibly other debugging
messages too) will be repeated multiple times.

$ perf bench sched messaging
# Running sched/messaging benchmark...
# 20 sender and receiver processes per group
# 10 groups == 400 processes run

Total time: 0.100 [sec]

$ perf bench sched messaging > result.txt
$ wc -l result.txt

In this file, there were so many "Running sched/messaging benchmark..."
lines. This was because stdout is converted to fully-buffered due to
the redirection and inherited child processes. Other lines are printed
after reaping all those tasks.

So fix it by flushing stdout before starting bench suites.

Cc: Hitoshi Mitake <>
Signed-off-by: Namhyung Kim <>
tools/perf/builtin-bench.c | 2 ++
1 file changed, 2 insertions(+)

diff --git a/tools/perf/builtin-bench.c b/tools/perf/builtin-bench.c
index cae9a5fd2ecf..afd1255a632f 100644
--- a/tools/perf/builtin-bench.c
+++ b/tools/perf/builtin-bench.c
@@ -159,6 +159,7 @@ static void all_suite(struct bench_subsys *subsys) /* FROM HERE */
printf("# Running %s/%s benchmark...\n",
+ fflush(stdout);

argv[1] = suites[i].name;
suites[i].fn(1, argv, NULL);
@@ -225,6 +226,7 @@ int cmd_bench(int argc, const char **argv, const char *prefix __maybe_unused)
printf("# Running %s/%s benchmark...\n",
+ fflush(stdout);
status = subsystems[i].suites[j].fn(argc - 1,
argv + 1, prefix);
goto end;

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