linux-kernel - Re: [PATCH 03/10] perf report: Apply --percent-limit to callchains also

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Date:	Wed, 3 Feb 2016 00:03:47 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Jiri Olsa <jolsa@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Andi Kleen <andi@...stfloor.org>,
	David Ahern <dsahern@...il.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Wang Nan <wangnan0@...wei.com>
Subject: Re: [PATCH 03/10] perf report: Apply --percent-limit to callchains
 also

On Tue, Feb 02, 2016 at 11:57:54AM -0300, Arnaldo Carvalho de Melo wrote:
> Em Tue, Feb 02, 2016 at 11:35:13PM +0900, Namhyung Kim escreveu:
> > On Tue, Feb 02, 2016 at 11:27:34AM -0300, Arnaldo Carvalho de Melo wrote:
> > > Em Tue, Feb 02, 2016 at 11:15:35PM +0900, Namhyung Kim escreveu:
> > > > On Tue, Feb 02, 2016 at 10:55:34AM -0300, Arnaldo Carvalho de Melo wrote:
> > > > > Em Tue, Feb 02, 2016 at 10:05:37PM +0900, Namhyung Kim escreveu:
> > > > > > Hi Arnaldo,
> > > > > > 
> > > > > > On Mon, Feb 01, 2016 at 05:19:36PM -0300, Arnaldo Carvalho de Melo wrote:
> > > > > > > Em Thu, Jan 28, 2016 at 12:40:50AM +0900, Namhyung Kim escreveu:
> > > > > > > > Currently --percent-limit option only works for hist entries.  However
> > > > > > > > it'd be better to have same effect to callchains as well
> > > > > > > 
> > > > > > > Documentation needs updating? It says:
> > > > > > > 
> > > > > > > --percent-limit::
> > > > > > >         Do not show entries which have an overhead under that percent.
> > > > > > >         (Default: 0).
> > > > > > 
> > > > > > Right.  Is it ok to you?
> > > > > > 
> > > > > > --percent-limit::
> > > > > >         Do not show entries and callchains which have an overhead under that
> > > > > >         percent.  (Default: 0).
> > > > > 
> > > > > Ok, but is the default zero?
> > > > > 
> > > > > That was what I was alluding to, as as soon as I applied the patch that
> > > > > made callchains honour this limit, about 60% of the entries in the
> > > > > particular perf.data file I was 'perf report'ing lost its '+' (callchain
> > > > > expansion) signs.
> > > > 
> > > > Yes, and this is what I want to say too. :)
> > > > 
> > > > The default value of percent limit is different for hist entry and
> > > > callchains.  For hist entry the default is 0, and for callchains it's
> > > > 0.5%.  But using --percent-limit option, we can set both at once from
> > > > now on.
> > > > 
> > > > Before this patchset, percent limit of callchains didn't checked.
> > > > Once applied, users can see callchains are disppeared like your case.
> > > >  This is just because 0.5% of the default limit for callchains is too
> > > > high IMHO - I guess it was originally set for 'fractal' mode which
> > > > calculates relative percents.  So I proposed to change the default in
> > > > the patch 10/10 but Andi thoughts 0.005% was too small.  We need to
> > > > choose other value like 0.05% ?
> > > 
> > > Unsure about the limit, but please fold the nice explanation you gave
> > > about the limits for hist entries and callchains and how the defaults
> > > are different, and how they can be set at once using --percent-limit.
> > 
> > Ok, will do.
> > 
> > > 
> > > Also, would it be overengineering to allow optionally set two limits,
> > > one for hists and one for callchains? I.e. like:
> > > 
> > >  --percent-limit 1,0.07
> > > 
> > > Then:
> > > 
> > >   --percent-limit 0.8
> > > 
> > > would be the same as:
> > > 
> > >   --percent-limit 0.8,0.8
> > 
> > Originally, the percent limit (threshold) for callchains can be set
> > using -g/--call-graph option.  What Andi asked is to set both limits
> > using a single option.  Not sure it's worth adding another way to
> > specify the callchain limit.
> 
> Ok, having that in the docs, i.e. when documenting --percent-limit
> mention that the callchain limit can be set via the -g option as well
> will help sort out confusion when trying to set those limits.

OK.  How about this?

--percent-limit::
	Do not show entries which have an overhead under that percent.
	(Default: 0).  Note that this option also sets percent limit (threshold)
	of callchains at once.  However the default value of callchain threshold
	is different than the default value of hist entries.  Please see
	--call-graph option for details.


> 
> And have you considered setting these limits dynamicly? I.e. in the TUI?

Oh, I forgot about it.  Will try to implement.

Thanks,
Namhyung