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

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Date:	Wed, 23 Apr 2014 08:09:38 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Namhyung Kim <namhyung@...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


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

> 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?

Yeah.

> 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

Yeah. Maybe make it:

    Filtered 13.2K out of 42.1K 'cycles' event samples

or so.

Thanks,

	Ingo
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