linux-kernel - Re: [PATCH] perf bench: flush stats when pipe it to a file or to tee

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Date:   Tue, 16 Nov 2021 00:41:51 +0200
From:   Sohaib Mohamed <sohaib.amhmd@...il.com>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:     rickyman7@...il.com, irogers@...gle.com,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Yury Norov <yury.norov@...il.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] perf bench: flush stats when pipe it to a file or to tee

Hello, Arnaldo

On Sat, Nov 13, 2021 at 09:18:22AM -0300, Arnaldo Carvalho de Melo wrote:
> Em Sat, Nov 13, 2021 at 09:16:42AM -0300, Arnaldo Carvalho de Melo escreveu:
> > Em Fri, Nov 12, 2021 at 11:53:12PM +0200, Sohaib Mohamed escreveu:
> > > 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.
> >
> > Good, now try with 'perf test' :-)
> >
> > Applying,
>
> Humm, take that back, when I almost did it for 'perf test' I used
> setvbuf(), take a look at it so that you don't have to go sprinkling
> fflush() calls and missing some places.
>
> - Arnaldo

I'm not sure about the meaning of 'perf test' here, Should I write new unit
tests?

I found I could invoke this function at the beginning of perf-bench:
setvbuf(stdout, NULL, _IONBF, 0);
This looks to me will resolve the issue for all perf-bench subcommands.
I'm not sure if a good practice...

This probably is version 2 of this patch:


diff --git a/tools/perf/builtin-bench.c b/tools/perf/builtin-bench.c
index d0895162c2ba..a0b812cde1ee 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 +246,8 @@ int cmd_bench(int argc, const char **argv)
        struct collection *coll;
        int ret = 0;

+       setvbuf(stdout, NULL, _IONBF, 0);
+
        if (argc < 2) {
                /* No collection specified. */
                print_usage();
@@ -300,7 +301,6 @@ 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;
                }



Thanks,
- Sohaib

>
> > - Arnaldo
> >
> > > 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 >
> > >
> > > 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@...il.com>
> > > Signed-off-by: Sohaib Mohamed <sohaib.amhmd@...il.com>
> > > ---
> > >  tools/perf/bench/find-bit-bench.c | 1 +
> > >  tools/perf/bench/synthesize.c     | 2 ++
> > >  2 files changed, 3 insertions(+)
> > >
> > > diff --git a/tools/perf/bench/find-bit-bench.c b/tools/perf/bench/find-bit-bench.c
> > > index 22b5cfe97023..39fb4184fbcb 100644
> > > --- a/tools/perf/bench/find-bit-bench.c
> > > +++ b/tools/perf/bench/find-bit-bench.c
> > > @@ -113,6 +113,7 @@ static int do_for_each_set_bit(unsigned int num_bits)
> > >
> > >  		if (use_of_val == accumulator)  /* Try to avoid compiler tricks. */
> > >  			printf("\n");
> > > +		fflush(stdout);
> > >  	}
> > >  	bitmap_free(to_test);
> > >  	return 0;
> > > diff --git a/tools/perf/bench/synthesize.c b/tools/perf/bench/synthesize.c
> > > index 7401ebbac100..d21d311df61b 100644
> > > --- a/tools/perf/bench/synthesize.c
> > > +++ b/tools/perf/bench/synthesize.c
> > > @@ -92,6 +92,7 @@ static int do_run_single_threaded(struct perf_session *session,
> > >  		update_stats(&event_stats, atomic_read(&event_count));
> > >  	}
> > >
> > > +	fflush(stdout);
> > >  	time_average = avg_stats(&time_stats);
> > >  	time_stddev = stddev_stats(&time_stats);
> > >  	printf("  Average %ssynthesis took: %.3f usec (+- %.3f usec)\n",
> > > @@ -186,6 +187,7 @@ static int do_run_multi_threaded(struct target *target,
> > >  		perf_session__delete(session);
> > >  	}
> > >
> > > +	fflush(stdout);
> > >  	time_average = avg_stats(&time_stats);
> > >  	time_stddev = stddev_stats(&time_stats);
> > >  	printf("    Average synthesis took: %.3f usec (+- %.3f usec)\n",
> > > --
> > > 2.25.1
> >
> > --
> >
> > - Arnaldo
>
> --
>
> - Arnaldo