Messages in this thread Patch in this message | | | From | Jiri Olsa <> | Subject | [PATCH 6/9] perf stat: Display time in precision based on std deviation | Date | Mon, 23 Apr 2018 11:08:20 +0200 |
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Ingo suggested to display elapsed time for multirun workload (perf stat -e) with precision based on the precision of the standard deviation.
In his own words:
> It would be better if perf stat would display elapsed time with a precision > adjusted to stddev, it should display at most 2 more significant digits than > the stddev inaccuracy. > > I.e. in the above case 0.39% is 0.109, so we only have accuracy for 1 digit, and > so we should only display 3: > > 27.988 seconds time elapsed ( +- 0.39% )
Plus suggestion about the output, which is small enough and connected with above change that I merged both changes together.
> Small output style nit - I think it would be nice if with --repeat the stddev was > also displayed in absolute values, besides percentage: > > 27.988 +- 0.109 seconds time elapsed ( +- 0.39% )
The output is now:
Performance counter stats for './perf bench sched pipe' (5 runs): SNIP 13.3667 +- 0.0256 seconds time elapsed ( +- 0.19% )
Suggested-by: Ingo Molnar <mingo@kernel.org> Link: http://lkml.kernel.org/n/tip-q10lhnqju8rdpiha542mvied@git.kernel.org Signed-off-by: Jiri Olsa <jolsa@kernel.org> --- tools/perf/builtin-stat.c | 30 ++++++++++++++++++++++++------ 1 file changed, 24 insertions(+), 6 deletions(-)
diff --git a/tools/perf/builtin-stat.c b/tools/perf/builtin-stat.c index 147a27e8c937..6b4f3d359cb3 100644 --- a/tools/perf/builtin-stat.c +++ b/tools/perf/builtin-stat.c @@ -1733,19 +1733,37 @@ static void print_header(int argc, const char **argv) } } +static int get_precision(double num) +{ + if (num > 1) + return 0; + + return lround(ceil(-log10(num))); +} + static void print_footer(void) { + double avg = avg_stats(&walltime_nsecs_stats) / NSEC_PER_SEC; FILE *output = stat_config.output; int n; if (!null_run) fprintf(output, "\n"); - fprintf(output, " %17.9f seconds time elapsed", - avg_stats(&walltime_nsecs_stats) / NSEC_PER_SEC); - if (run_count > 1) { - fprintf(output, " "); - print_noise_pct(stddev_stats(&walltime_nsecs_stats), - avg_stats(&walltime_nsecs_stats)); + + if (run_count == 1) { + fprintf(output, " %17.9f seconds time elapsed", avg); + } else { + double sd = stddev_stats(&walltime_nsecs_stats) / NSEC_PER_SEC; + /* + * Display at most 2 more significant + * digits than the stddev inaccuracy. + */ + int precision = get_precision(sd) + 2; + + fprintf(output, " %17.*f +- %.*f seconds time elapsed", + precision, avg, precision, sd); + + print_noise_pct(sd, avg); } fprintf(output, "\n\n"); -- 2.13.6
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