linux-kernel - Re: [RFC/PATCH 0/4] perf report: Support folded callchain output (v2)

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Message-ID: <20151102224927.GA11498@danjae.kornet>
Date:	Tue, 3 Nov 2015 07:49:27 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	Arnaldo Carvalho de Melo <acme@...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)

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? :)

I'm not insisting it strongly, but it's a bit strange for me if perf
report doesn't show any hist lines..


> 
> > 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. :)


> 
> 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
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?

Thanks,
Namhyung
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