linux-kernel - Re: [RFC/PATCHSET 00/14] perf report: Add support to accumulate hist periods (v2)

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Date:	Mon, 11 Nov 2013 13:13:52 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Namhyung Kim <namhyung@...nel.org>,
	Pekka Enberg <penberg@...nel.org>,
	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>,
	Stephane Eranian <eranian@...gle.com>,
	Jiri Olsa <jolsa@...hat.com>,
	Rodrigo Campos <rodrigo@...g.com.ar>,
	Arun Sharma <asharma@...com>
Subject: Re: [RFC/PATCHSET 00/14] perf report: Add support to accumulate hist
 periods (v2)


* Frederic Weisbecker <fweisbec@...il.com> wrote:

> On Wed, Nov 06, 2013 at 12:47:01PM +0100, Ingo Molnar wrote:
> > 
> > * Namhyung Kim <namhyung@...nel.org> wrote:
> > 
> > > On Wed, 6 Nov 2013 09:30:46 +0100, Ingo Molnar wrote:
> > > > * Namhyung Kim <namhyung@...nel.org> wrote:
> > > >
> > > >> Hi Ingo,
> > > >> 
> > > >> On Tue, 5 Nov 2013 12:58:02 +0100, Ingo Molnar wrote:
> > > >> > * Namhyung Kim <namhyung@...nel.org> wrote:
> > > >> >> But the 'cumulative' (btw, I feel a bit hard to type this word..) is 
> > > >> >> different in that it *generates* entries didn't get sampled originally. 
> > > >> >> And as it requires callchains, total field will not work if callchains 
> > > >> >> are missing.
> > > >> >
> > > >> > Well, 'total' should disappear if it's not available.
> > > >> 
> > > >> But what if it's the only sort key user gave?
> > > >
> > > > Do you mean something like:
> > > >
> > > >   -F self,name -s total
> > > >
> > > > i.e. if a sort key not displayed?
> > > 
> > > What I worry is when no -F option was given at all.
> > 
> > In that case the default list applied, plus whatever new fields are 
> > mentioned in -s would also be added (appended or prepended).
> > 
> > The display order of columns should _probably_ be something like:
> > 
> >   key1 key2 ... non-key1 non-key2
> > 
> > there's not much point in sorting and then displaying the key not in 
> > front, right?
> > 
> > > > I think sort keys should be automatically added to the displayed 
> > > > fields list.
> > > 
> > > Agreed.
> > 
> > > > This problem should be solved if all -s fields are displayed - i.e. 
> > > > they are added to the -F list, right?
> > > 
> > > But old users might not aware of the new -F option, and use -s option 
> > > only.  If so, she will get output like the first example, right?
> > 
> > Well, there's a default -F list that applies - so this shouldn't be a 
> > problem, agreed? So output should be like the second (expected) example.
> > 
> > > > Basically there's just a single concept: the -F list. The -s option 
> > > > simply modifies and extends the -F list but internally perf report 
> > > > would not know anything about '-s', it only knows about fields to 
> > > > display and it would know which of those fields are to be sorted and 
> > > > in what order.
> > > >
> > > > Does that make sense to you? Does it cover everything needed?
> > > 
> > > I like the concept.  I'm just looking for a way to add it without 
> > > upsetting old users. :)
> > 
> > If the default -F list matches our current displayed fields list then 
> > there should not be much change in behavior (beyond the addition of total 
> > for call-graph outputs - which can be kept completely separate).
> > 
> > I'm not too worried about call-graph 'legacies': it generates such huge 
> > perf.data files which is parsed so slowly at the moment that there's very 
> > little user base ... Anyone who absolutely needs call-graph profiling uses 
> > SysProf which performs well.
> 
> I'm a bit confused by what will be changed with call-graph here. Also 
> I've seen perf callgraph reports quite often on emails not even related 
> to perf developement. It doesn't appear to me like an irrelevant 
> feature...

It's not an irrelevant feature at all! :-)

It's just that for any sort of longer profile it was pretty 
difficult/frustrating to use, which I think held back adoption.

That performance problem got fixed now by you and Namhyung, so I think 
we'll see even wider adoption of call-graph profiling...

Thanks,

	Ingo
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