Message-ID: <20151102230436.GD21609@kernel.org>
Date:	Mon, 2 Nov 2015 20:04:36 -0300
From:	Arnaldo Carvalho de Melo <acme@...nel.org>
To:	Namhyung Kim <namhyung@...nel.org>
Cc:	Brendan Gregg <brendan.d.gregg@...il.com>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Jiri Olsa <jolsa@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	David Ahern <dsahern@...il.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Andi Kleen <andi@...stfloor.org>,
	Kan Liang <kan.liang@...el.com>
Subject: Re: [RFC/PATCH 0/4] perf report: Support folded callchain output (v2)

Em Tue, Nov 03, 2015 at 07:49:27AM +0900, Namhyung Kim escreveu:
> On Mon, Nov 02, 2015 at 07:28:42PM -0300, Arnaldo Carvalho de Melo wrote:
> > Hi Namhyung,
> > 
> > Em Tue, Nov 03, 2015 at 07:12:04AM +0900, Namhyung Kim escreveu:
> > > On Mon, Nov 02, 2015 at 06:30:21PM -0300, Arnaldo Carvalho de Melo wrote:
> > > > Em Mon, Nov 02, 2015 at 12:37:28PM -0800, Brendan Gregg escreveu:
> > > > > On Mon, Nov 2, 2015 at 4:57 AM, Namhyung Kim <namhyung@...nel.org> wrote:
> > > > > > This is what Brendan requested on the perf-users mailing list [1] to
> > > > > > support FlameGraphs [2] more efficiently.  This patchset adds a few
> > > > > > more callchain options to adjust the output for it.
> > 
> > > > > > At first, 'folded' output mode was added.  The folded output puts all
> > > > > > calchain nodes in a line separated by semicolons, a space and the
> > > > > > value.  Now it only supports --stdio as other UI provides some way of
> > > > > > folding/expanding callchains dynamically.
> > 
> > > > > > The value is now can be one of 'percent', 'period', or 'count'.  The
> > > > > > percent is current default output and the period is the raw number of
> > > > > > sample periods.  The count is the number of samples for each callchain.
> > 
> > > > > > Here's an example:
> > 
> > > > > >   $ perf report --no-children --show-nr-samples --stdio -g folded,count
> > > > > >   ...
> > > > > >     39.93%     80  swapper  [kernel.vmlinux]  [k] intel_idel
> > > > > >   intel_idle;cpuidle_enter_state;cpuidle_enter;call_cpuidle;cpu_startup_entry;start_secondary 57
> > > > > >   intel_idle;cpuidle_enter_state;cpuidle_enter;call_cpuidle;cpu_startup_entry;rest_init;... 23
> > 
> > > > > So for the folded output I don't need the summary line (the row of
> > > > > columns printed by hist_entry__snprintf()), and don't need anything
> > > > > except folded stacks and the counts. If working with the existing
> > > > > stdio interface is making it harder than it needs to be, might it be
> > 
> > > > I don't think it so, just add some flag asking for that
> > > > hist_entry__snprintf() to be supressed, ideas for a long option name?
> > 
> > > > Having it as Namhyung did may have value for some people as a more
> > > > compact way to show the callchains together with the hist_entry line.
> > 
> > > Yeah, I'd keep the hist entry line unless it's too hard to
> > > parse/filter.  IMHO it's just a way to show callchains, so no need to
> > 
> > What I suggested was to have something like:
> > 
> >   $ perf report --no-children --no-hists --stdio -g folded,count
> >                               ^^^^^^^^^^
> >                               ^^^^^^^^^^
> >   ...
> >   intel_idle;cpuidle_enter_state;cpuidle_enter;call_cpuidle;cpu_startup_entry;start_secondary 57
> >   intel_idle;cpuidle_enter_state;cpuidle_enter;call_cpuidle;cpu_startup_entry;rest_init;... 23
> > 
> > I.e. the first entry in the callchain is 'intel_idle', just like in what
> > Brendan called the 'summary line', i.e. reduntant when what he wants its
> > just all the callchains and how many times they were sampled.
> 
> Yep, I know.  But isn't 'perf report' all for seeing hist lines? :)

Well, so far, yes, but he is presenting a usecase where what we want to
see is just callchains, and we can achieve that rather easily, no?
 
> I'm not insisting it strongly, but it's a bit strange for me if perf
> report doesn't show any hist lines..

If that is of no use in this use case, why not?

> > > have separate output mode..
> >  
> > > Brendan, I guess you still need to know other info like cpu or pid, no?
> > 
> > Possibly, but just with the callchains he has enough info for the basic
> > flame graph, no?
> >  
> > > And I feel like it'd be better to put the count before the callchains
> > > for consistency like below.  Is it OK to you?
> > 
> > Consistency with what?
> 
> Oh, I meant consistency with other callchain output style like graph,
> fractal or flat - They all show the numbers before callchains.  And I
> think it's easier to read for human. :)

Well, As I said, isn't the main object here the callchain? :-)

And Brendan's request is for a something to be consumed by scripts, i.e.
something like we have for perf stat:

For humans:

[root@...icio ~]# perf stat -e cycles -I 1000 -a
#           time             counts unit events
     1.000304391          1,820,038      cycles                   
     2.000490191      1,005,477,007      cycles                   
     3.000657813          1,717,007      cycles                   
^C     3.917890293          2,804,034      cycles                   

For machines/scripts:

[root@...icio ~]# perf stat -x, -e cycles -I 1000 -a
     1.000291954,1923360,,cycles,3998167210,100.00
     2.000477154,1005608105,,cycles,3998475482,100.00
     3.000612612,1345483,,cycles,3998332391,100.00
     4.000744469,1005046913,,cycles,3998258199,100.00
^C     4.331684347,1551327,,cycles,3463190970,100.00

[root@...icio ~]#

 
> > The main thing here is the callchain, all the other stuff are things
> > related to it, so showing it first makes sense to me.
> > 
> > Having some way to list the desired info to have for each callchain may
> > be interesting, and if he could do it like:
> > 
> >    -g folded,count,cpu,other,fields
> > 
> > then he would know how to parse the per-callchain info at the end of
> > each line, right?
> 
> Hmm.. looks like that it ends up having redundant info.  I don't think

What is redundant, and with with what? 

> it's generally useful to other 'perf report' stuffs.  Wouldn't it be
> better just adding minimal support and let the external tool parse the
> output?

Oh well, perhaps we could have a 'perf callchain' tool that would be
centered on callchains and would provided one line per callchain, which
would have:

callchain;seprarated;colons series,of,desired,fields,for,this,callchain

Which would reuse heavily the 'perf report' / 'perf top' code for
histograms, no?

I still think that this is a 'perf report' thing, but one that is
centered in callchains, and that is to be consumed by scripts, not
humans.

- Arnaldo
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