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

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Date:	Fri, 1 Nov 2013 08:55:02 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Namhyung Kim <namhyung@...nel.org>,
	Pekka Enberg <penberg@...nel.org>
Cc:	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>,
	Frederic Weisbecker <fweisbec@...il.com>,
	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)


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

> > A couple of details:
> >
> > 1)
> >
> > This is pretty close to SysProf output, right? So why not use the 
> > well-known SysProf naming and call the first column 'self' and the 
> > second column 'total'? I think those names are pretty intuitive and 
> > it would help people who come from SysProf over to perf.
> 
> Okay, I can do it. (Although sysprof seems to call it 'cumulative'
> rather than 'total' - but I think the 'total' is better since it's
> simpler and shorter.)

So sysprof-1.2 has the following two windows:

 'functions',   with 'self' and 'total' fields
 'descendants', with 'self' and 'cumulative' fields

'descendants' appears to be similar to the perf 'dso' concept.

> > 2)
> >
> > Is it possible to configure the default 'report -g' style, so that 
> > people who'd like to use it all the time don't have to type '-g 
> > cumulative' all the time?
> 
> Hmm.. maybe I can add support for the 'report.call-graph' config option.

If we display your new 'total' field by default then it's not as 
pressing to me :)

> > 3)
> >
> > I'd even argue that we enable this reporting feature by default, if 
> > a data file includes call-chain data: the first column will still 
> > show the well-known percentage that perf report produces today, the 
> > second column will be a new feature in essence.
> >
> > The only open question would be, by which column should we sort: 
> > 'sysprof style' sorts by 'total', 'perf style' sorts by 'self'. 
> > Agreed?
> 
> Right, I defaulted to go by 'total'.  But we can add an option for 
> it.

The purpose would be to allow people to do old-style 'sort by 
function overhead' output, while still seeing the 'total' field as 
well.

Btw., if anyone is interested in improving the GTK front-end, it 
would be _really_ nice if it had a 'start profiling' button like 
sysprof has today, with a 'samples' field showing the current number 
of samples. (We could even improve upon sysprof by adding 'stop' 
functionality as well ;-)

A bit like perf top, except the reporting session is hidden until 
the user actively requests the profile.

Maybe it could even be called a gtk version of 'perf top', with a 
button to start/stop collection, with another button to 
activate/deactivate reporting output, and yet another button to 
reset the profiling buffer.

With that feature set perf would be a ready sysprof workflow 
replacement I think. (I've Cc:-ed Pekka, just in case! :-)

> > 4)
> >
> > This is not directly related to the new feature you added: 
> > call-graph profiling still takes quite a bit of time. It might 
> > make sense to save the ordered histogram to a perf.data.ordered 
> > file, so that repeat invocations of 'perf report' don't have to 
> > recalculate everything again and again?
> >
> > This file would be maintained transparently and would only be 
> > re-created when the perf.data file changes, or something like 
> > that.
> 
> Hmm.. good idea.  We may discuss it along with Jiri's multiple 
> file storage patches.  I haven't had a time to review - maybe next 
> week.

So Arnaldo tells me that with your and Frederic's latest 
callgraph-speedup patches the parsing of perf.data got _really_ 
fast, so maybe my performance complaint is moot and we should delay 
complicating the primary perf.data file model with a 'cache' until 
your patches are in and we see the full impact.

Thanks,

	Ingo
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