linux-kernel - Re: [RFC/PATCHSET 00/18] perf report: Add support to accumulate hist periods (v3)

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Date:	Wed, 18 Dec 2013 10:46:22 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Namhyung Kim <namhyung@...nel.org>
Cc:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Paul Mackerras <paulus@...ba.org>,
	Namhyung Kim <namhyung.kim@....com>,
	LKML <linux-kernel@...r.kernel.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Arun Sharma <asharma@...com>, Jiri Olsa <jolsa@...hat.com>,
	Rodrigo Campos <rodrigo@...g.com.ar>
Subject: Re: [RFC/PATCHSET 00/18] perf report: Add support to accumulate hist
 periods (v3)


* Namhyung Kim <namhyung@...nel.org> wrote:

> I changed the option as a separate --cumulate and added a new 
> "Total" column (and renamed the default "Overhead" column into 
> "Self").  The output will be sorted by total (cumulative) overhead 
> for now.  The reason I changed to the --cumulate is that I still 
> think it's much different from other --callchain options and I plan 
> to add support for showing (remaining) callchains to cumulative 
> entries too.  The --callchain option will take care of it even with 
> --cumulate option.

So I still think this is a fantastic feature, and while this variant 
of the user interface is an improvement over the previous version, we 
are not there yet ;-)

My main complaint that any variation of 'cumulative' or 'cumulate' is 
a tongue-twister to users. I certainly won't be able to remember it 
and will have to call up the manpage every time I use it - which will 
be very annoying. I'd probably not use the feature much.

So lets approach this from the casual user's angle. Casual users don't 
really remember twisted names for command line options, they remember 
the big picture, big concepts, and they remember bits of the output:

> When the -g cumulative option is given, it'll be shown like this:
> 
>   $ perf report --cumulate --stdio
> 
>   #     Self     Total  Command      Shared Object                   Symbol
>   # ........  ........  .......  .................  .......................
>   #
>        0.00%    88.29%      abc  libc-2.17.so       [.] __libc_start_main  
>        0.00%    88.29%      abc  abc                [.] main               
>        0.00%    88.29%      abc  abc                [.] c                  
>        0.00%    88.29%      abc  abc                [.] b                  
>       88.29%    88.29%      abc  abc                [.] a                  
>        0.00%    11.61%      abc  ld-2.17.so         [.] _dl_sysdep_start   

So the natural way to get this would something like:

	perf report --total

Or, if '--total' does not feel good, maybe we should change 'Total' to 
'Siblings' or 'Children', and propagate that naming through the UI:

   $ perf report --children --stdio
 
   #     Self  Children  Command      Shared Object                   Symbol
   # ........  ........  .......  .................  .......................
   #
        0.00%    88.29%      abc  libc-2.17.so       [.] __libc_start_main  
        0.00%    88.29%      abc  abc                [.] main               
        0.00%    88.29%      abc  abc                [.] c                  
        0.00%    88.29%      abc  abc                [.] b                  
       88.29%    88.29%      abc  abc                [.] a                  
        0.00%    11.61%      abc  ld-2.17.so         [.] _dl_sysdep_start   

Which shows the sum of overhead of all child functions as well, not 
just ourselves.

Anything but 'cumulative'. That word, beyond being a strange, hard to 
remember Latin word, also does not tell the user (or the developer) 
anything about _what_ is being accumulated. It could cover anything.

I also think this option should be enabled by default - lets see how 
much people complain about that.

Okay?

Thanks,

	Ingo
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