linux-kernel - Re: [PATCH v1] perf stat display: Make %f precision consistent

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Message-ID: <aThgIB2VQdAtEXKm@gmail.com>
Date: Tue, 9 Dec 2025 18:45:04 +0100
From: Ingo Molnar <mingo@...nel.org>
To: Ian Rogers <irogers@...gle.com>
Cc: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Namhyung Kim <namhyung@...nel.org>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Jiri Olsa <jolsa@...nel.org>,
	Adrian Hunter <adrian.hunter@...el.com>,
	James Clark <james.clark@...aro.org>,
	Chun-Tse Shao <ctshao@...gle.com>, linux-perf-users@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] perf stat display: Make %f precision consistent

* Ian Rogers <irogers@...gle.com> wrote:

> Commit bc22de9bcdb2 ("perf stat: Display time in precision based on
> std deviation") added multirun workload elapsed time. There was an
> effort to make the precision in the output most useful for the user,
> however, when gathering over runs it means the formatting varies. This
> change just makes the output format fixed.
>
> Before:
> ```
> $ while :; do perf stat --null --repeat 3 sleep 0.1 2>&1 | grep elapsed; done
>           0.101140 +- 0.000149 seconds time elapsed  ( +-  0.15% )
>          0.1011396 +- 0.0000218 seconds time elapsed  ( +-  0.02% )
>           0.101331 +- 0.000124 seconds time elapsed  ( +-  0.12% )
> ^C
> $ while :; do perf stat --null --repeat 3 sleep 1 2>&1 | grep elapsed; done
>           1.001317 +- 0.000146 seconds time elapsed  ( +-  0.01% )
>           1.001377 +- 0.000172 seconds time elapsed  ( +-  0.02% )
>            1.00253 +- 0.00131 seconds time elapsed  ( +-  0.13% )
> ```
>
> After:
> ```
> $ while :; do perf stat --null --repeat 3 sleep 0.1 2>&1 | grep elapsed; done
>        0.101406408 +- 0.000064778 seconds time elapsed  ( +-  0.06% )
>        0.101367315 +- 0.000027253 seconds time elapsed  ( +-  0.03% )
>        0.101434164 +- 0.000084750 seconds time elapsed  ( +-  0.08% )
> ^C
> $ while :; do perf stat --null --repeat 3 sleep 1 2>&1 | grep elapsed; done
>        1.001525467 +- 0.000051703 seconds time elapsed  ( +-  0.01% )
>        1.001375093 +- 0.000116200 seconds time elapsed  ( +-  0.01% )
>        1.001141025 +- 0.000046361 seconds time elapsed  ( +-  0.00% )

Perfect, thank you!

Tested-by: Ingo Molnar <mingo@...nel.org>

	Ingo