Date:	Tue, 14 Jan 2014 09:15:32 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
Cc:	Jiri Olsa <jolsa@...hat.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Paul Mackerras <paulus@...ba.org>,
	Ingo Molnar <mingo@...nel.org>,
	Namhyung Kim <namhyung.kim@....com>,
	LKML <linux-kernel@...r.kernel.org>,
	Arun Sharma <asharma@...com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Rodrigo Campos <rodrigo@...g.com.ar>
Subject: Re: [PATCH 01/28] perf tools: Insert filtered entries to hists also

Hi Arnaldo,

On Thu, 9 Jan 2014 11:37:24 -0300, Arnaldo Carvalho de Melo wrote:
> Em Thu, Jan 09, 2014 at 09:57:35PM +0900, Namhyung Kim escreveu:
>> 2014-01-08 (수), 15:59 -0300, Arnaldo Carvalho de Melo:
>> > Em Wed, Jan 08, 2014 at 05:22:53PM +0100, Jiri Olsa escreveu:
>> > > On Wed, Jan 08, 2014 at 09:41:13AM -0300, Arnaldo Carvalho de Melo wrote:
>> > > > Em Wed, Jan 08, 2014 at 05:46:06PM +0900, Namhyung Kim escreveu:
>> > > > > Currently if a sample was filtered by command line option, it just
>> > > > > dropped.  But this affects final output in that the percentage can be
>> > > > > different since the filtered entries were not included to the total.
>> > > > > 
>> > > > > For example, if an original output looked like below:
>> > > > 
>> > > > Humm, if one says that he/she is interested on just samples for a and b,
>> > > > the current behaviour will state how many of the filtered samples are
>> > > > for a and b, which is valid.
>> > > > 
>> > > >  I bet the number of samples will reflect that as well, but you filtered
>> > > > it out, yes, it stays there, so the percentages are relative to the
>> > > > number of samples.
>> > > > 
>> > > > So I think this change in behaviour is wrong, no?
>
>> > > haven't checked the implementation yet, but it kind of does
>> > > what I'd expect for symbol filtering:
>
>> > > perf report
>> > > ...
>> > >  22.00%  yes  libc-2.17.so       [.] __strlen_sse2
>> > >  11.79%  yes  libc-2.17.so       [.] fputs_unlocked
>> > >   9.65%  yes  libc-2.17.so       [.] __GI___mempcpy
>> > >   1.91%  yes  yes                [.] fputs_unlocked@plt
>> > > ...
>> > > 
>> > > search (press '/') for fputs_unlocked (with Namhyung's change):
>> > >  11.79%  yes  libc-2.17.so  [.] fputs_unlocked
>> > >   1.91%  yes  yes           [.] fputs_unlocked@plt
>> > > 
>> > > while the current one shows:
>> > >  86.08%  yes  libc-2.17.so  [.] fputs_unlocked
>> > >  13.92%  yes  yes           [.] fputs_unlocked@plt
>> > > 
>> > > which annoys me when searching for 'invisible' symbol
>> > > within tons of others.. I had to do that grep thing
>> > > you showed.
>> > > 
>> > > I'd like to have the Namhyung's change behaviour as default,
>> > > but I'll be happy with some switch as well ;-)
>> > 
>> > I understand the desire for this different mode, looks indeed useful.
>> 
>> Yeah, the above is the reason why I wrote this firstly.  And then I
>> thought it should be applied to the command line filter options too.
>
> I don't have a problem with providing a new option, but for those who
> think that when you filter samples based on some criteria the
> percentages that should appear should be relative to the new, filtered,
> total_period, that is a change in behaviour, so needs to be switchable.
>  
>> > So I think that this is a new feature and as so we should provide it as
>> > an option, that may (or not) become the default.
>> > 
>> > Some concerns I have are that when we go on filtering we have to have
>> > all the things that are zeroed to then get accrued for each hist entry
>> > that matches the filter being applied and now at least a nr_entries
>> > field got out of the if (al.filtered) block, i.e. in the end we will
>> > have the number of hist entries entries filtered but continue having the
>> > total period for all (filtered or not) hist entries.
>  
>> One thing related to it is when --children option is used.  Since total
>> period is added only for a real sample, if the sample is filtered but
>> the parents are not, the parents might have more than 100% overhead.
>
> So when implementing the new option this has to be taken into account,
> no problem (haven't really thought about the full implications here).
>  
>> > Having it as a separate feature would allow to have both views:
>> > 
>> > 1. the percentages relative to the filtered samples
>> > 2. the percentages relative to all (filtered or not) samples
>> > 
>> > Being selectable on the command line and also with a hotkey to provide
>> > two columns: %total, %filtered.
>> 
>> Hmm.. do you really want two columns instead of single column and a
>> switch/option?  Then the (second) %filtered column will be shown up only
>> if filtering is enabled.  Isn't it annoying for a dynamic filtering
>> (i.e. '/' key on TUI)?
>
> Hey, I'm not the one to decide this :-)
>
> There _are_ two choices for how the percentage gets computed, if one
> wants one, the other, or both, well, the hard part here is to decide the
> default, but there are two options, showing one, the other or both
> should be left to the user, even if after one or two keystrokes :)

So I'd like to make this changed behavior as default like Jiri said.

But adding a new percentage column will be a headache since it'll
increase the combination of current behavior - total x sys/user x group
x children - I'd really want to keep it small..

What about just adding --percentage <relative|absolute> option and make
"absolute" default (it can also be changed via config option, of course)?

Thanks,
Namhyung
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