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 <[email protected]>
Link: http://lkml.kernel.org/n/[email protected]
Signed-off-by: Jiri Olsa <[email protected]>
---
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
