perf bench: Use unbuffered output when pipe/tee'ing to a file

The output of 'perf bench' gets buffered when I pipe it to a file or to
tee, in such a way that I can see it only at the end.

E.g.

  $ perf bench internals synthesize -t
  < output comes out fine after each test run >

  $ perf bench internals synthesize -t | tee file.txt
  < output comes out only at the end of all tests >

This patch resolves this issue for 'bench' and 'test' subcommands.

See, also:

  $ perf bench mem all | tee file.txt
  $ perf bench sched all | tee file.txt
  $ perf bench internals all -t | tee file.txt
  $ perf bench internals all | tee file.txt

Committer testing:

It really gets staggered, i.e. outputs in bursts, when the buffer fills
up and has to be drained to make up space for more output.

Suggested-by: Riccardo Mancini <rickyman7@gmail.com>
Signed-off-by: Sohaib Mohamed <sohaib.amhmd@gmail.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Acked-by: Jiri Olsa <jolsa@redhat.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Fabian Hemmer <copy@copy.sh>
Cc: Ian Rogers <irogers@google.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lore.kernel.org/lkml/20211119061409.78004-1-sohaib.amhmd@gmail.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

1 files changed, 3 insertions, 0 deletions

diff --git a/tools/perf/tests/builtin-test.c b/tools/perf/tests/builtin-test.c
index f1e6d2a3a578..1fb9f2a11d63 100644
--- a/tools/perf/tests/builtin-test.c
+++ b/tools/perf/tests/builtin-test.c
@@ -607,6 +607,9 @@ int cmd_test(int argc, const char **argv)
         if (ret < 0)
                 return ret;
 
+	/* Unbuffered output */
+	setvbuf(stdout, NULL, _IONBF, 0);
+
 	argc = parse_options_subcommand(argc, argv, test_options, test_subcommands, test_usage, 0);
 	if (argc >= 1 && !strcmp(argv[0], "list"))
 		return perf_test__list(argc - 1, argv + 1);