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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: > 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> |
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README |
Linux kernel ============ There are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. Please read Documentation/admin-guide/README.rst first. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. The formatted documentation can also be read online at: https://www.kernel.org/doc/html/latest/ There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.