[PATCH v2] Unbuffered output when pipe/tee to a file

[Sohaib Mohamed]

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

Suggested-by: Riccardo Mancini <rickyman7@xxxxxxxxx>
Signed-off-by: Sohaib Mohamed <sohaib.amhmd@xxxxxxxxx>
---
v1 -> v2:
- Use setvbuf(), instead of sprinkling fflush() calls and missing some places.

v1: https://lore.kernel.org/linux-perf-users/20211112215313.108823-1-sohaib.amhmd@xxxxxxxxx/
---
 tools/perf/builtin-bench.c      | 5 +++--
 tools/perf/tests/builtin-test.c | 3 +++
 2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/tools/perf/builtin-bench.c b/tools/perf/builtin-bench.c
index d0895162c2ba..d291f3a8af5f 100644
--- a/tools/perf/builtin-bench.c
+++ b/tools/perf/builtin-bench.c
@@ -226,7 +226,6 @@ static void run_collection(struct collection *coll)
 		if (!bench->fn)
 			break;
 		printf("# Running %s/%s benchmark...\n", coll->name, bench->name);
-		fflush(stdout);

 		argv[1] = bench->name;
 		run_bench(coll->name, bench->name, bench->fn, 1, argv);
@@ -247,6 +246,9 @@ int cmd_bench(int argc, const char **argv)
 	struct collection *coll;
 	int ret = 0;

+	/* Unbuffered output */
+	setvbuf(stdout, NULL, _IONBF, 0);
+
 	if (argc < 2) {
 		/* No collection specified. */
 		print_usage();
@@ -300,7 +302,6 @@ int cmd_bench(int argc, const char **argv)

 			if (bench_format == BENCH_FORMAT_DEFAULT)
 				printf("# Running '%s/%s' benchmark:\n", coll->name, bench->name);
-			fflush(stdout);
 			ret = run_bench(coll->name, bench->name, bench->fn, argc-1, argv+1);
 			goto end;
 		}
diff --git a/tools/perf/tests/builtin-test.c b/tools/perf/tests/builtin-test.c
index 8cb5a1c3489e..d92ae4efd2e6 100644
--- a/tools/perf/tests/builtin-test.c
+++ b/tools/perf/tests/builtin-test.c
@@ -606,6 +606,9 @@ 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);
--
2.25.1