linux-kernel - Re: [PATCH 1/3] perf mem: Describe overhead calculation in brief

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Message-ID: <20250527101246.GG2566836@e132581.arm.com>
Date: Tue, 27 May 2025 11:12:46 +0100
From: Leo Yan <leo.yan@....com>
To: Namhyung Kim <namhyung@...nel.org>
Cc: Arnaldo Carvalho de Melo <acme@...nel.org>,
	Ian Rogers <irogers@...gle.com>,
	Kan Liang <kan.liang@...ux.intel.com>, Jiri Olsa <jolsa@...nel.org>,
	Adrian Hunter <adrian.hunter@...el.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>, LKML <linux-kernel@...r.kernel.org>,
	linux-perf-users@...r.kernel.org,
	Ravi Bangoria <ravi.bangoria@....com>,
	Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH 1/3] perf mem: Describe overhead calculation in brief

On Fri, May 23, 2025 at 03:21:55PM -0700, Namhyung Kim wrote:
> From: Ravi Bangoria <ravi.bangoria@....com>
> 
> Unlike perf-report which uses sample period for overhead calculation,
> perf-mem overhead is calculated using sample weight. Describe perf-mem
> overhead calculation method in it's man page.
> 
> Signed-off-by: Ravi Bangoria <ravi.bangoria@....com>
> Signed-off-by: Namhyung Kim <namhyung@...nel.org>

For whole series:

Reviewed-by: Leo Yan <leo.yan@....com>

> ---
>  tools/perf/Documentation/perf-mem.txt | 19 +++++++++++++++++++
>  1 file changed, 19 insertions(+)
> 
> diff --git a/tools/perf/Documentation/perf-mem.txt b/tools/perf/Documentation/perf-mem.txt
> index a9e3c71a220557d4..965e73d377724607 100644
> --- a/tools/perf/Documentation/perf-mem.txt
> +++ b/tools/perf/Documentation/perf-mem.txt
> @@ -137,6 +137,25 @@ REPORT OPTIONS
>  In addition, for report all perf report options are valid, and for record
>  all perf record options.
>  
> +OVERHEAD CALCULATION
> +--------------------
> +Unlike linkperf:perf-report[1], which calculates overhead from the actual
> +sample period, perf-mem overhead is calculated using sample weight. E.g.
> +there are two samples in perf.data file, both with the same sample period,
> +but one sample with weight 180 and the other with weight 20:
> +
> +  $ perf script -F period,data_src,weight,ip,sym
> +  100000    629080842 |OP LOAD|LVL L3 hit|...     20       7e69b93ca524 strcmp
> +  100000   1a29081042 |OP LOAD|LVL RAM hit|...   180   ffffffff82429168 memcpy
> +
> +  $ perf report -F overhead,symbol
> +  50%   [.] strcmp
> +  50%   [k] memcpy
> +
> +  $ perf mem report -F overhead,symbol
> +  90%   [k] memcpy
> +  10%   [.] strcmp
> +
>  SEE ALSO
>  --------
>  linkperf:perf-record[1], linkperf:perf-report[1], linkperf:perf-arm-spe[1]
> -- 
> 2.49.0.1151.ga128411c76-goog
>