linux-kernel - Re: [PATCHSET 0/9] perf tools: Fixup for the --percentage change

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Date:	Wed, 23 Apr 2014 13:49:05 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Jiri Olsa <jolsa@...hat.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Paul Mackerras <paulus@...ba.org>,
	Namhyung Kim <namhyung.kim@....com>,
	LKML <linux-kernel@...r.kernel.org>,
	David Ahern <dsahern@...il.com>,
	Andi Kleen <andi@...stfloor.org>
Subject: Re: [PATCHSET 0/9] perf tools: Fixup for the --percentage change

Hi Ingo,

On Tue, 22 Apr 2014 11:55:57 +0200, Ingo Molnar wrote:
> I gave it some quick testing and after fixing a trivial merge conflict 
> in tools/lib/lockdep/Makefile all seems to be working fine.

Thanks for testing!

>
> But while looking at it I remembered one of my old UI complains about 
> perf top and report, the hard to read nature of:
>
>    Event count (approx.): 226958779
>
> the values displayed are typically way too large to be easily human 
> readable. More importantly, they are also nonsensical! That we have a 
> sampling interval and can sum up all the intervals sampled has very 
> little meaning to the overwhelming majority of humans looking at the 
> data.
>
> And printing that just spams the visual field and confuses people.
>
> People care about the quality and speed of sampling itself, not 
> directly the interval of sampling (which will often be variable with 
> auto-freq sampling).

You meant 'period' by 'interval', right?

There's --show-total-period option (should be equivalent to -F period
later) in perf report, so there might be people want to see the numbers
IMHO.

>
> So instead of:
>
>   Samples: 42K of event 'cycles', Event count (approx.): 226958779
>
> How about only printing this in 'perf top' and 'perf report':
>
>   Captured 42.1K 'cycles' event samples
>
> Note the extra decimal (which helps monitor smaller changes as well), 
> and note the different wording.
>
> Thoughts?

Well, I'm okay to add the extra decimal, but it seems that it only makes
sense when the unit is 'K'..

And I think it might be worth adding filtered sample count as well if
filtering is enabled something like:

  Captured 13.2K/42.1K 'cycles' event samples


Thanks,
Namhyung
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