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:
> This output is a slightly bit misleading:
> Performance counter stats for 'make -j128' (10 runs):
> 27.988995256 seconds time elapsed ( +- 0.39% )
> The 9 significant digits in the result, while only 1 is valid, suggests accuracy
> where none exists.
> 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 a suggestion about the output, which is small enough and connected
with the 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>
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20180423090823.32309-7-jolsa@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
bc22de9bcd