linux-kernel - Re: [PATCHSET 0/4] perf report: Support folded callchain output (v4)

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Message-ID: <20151104145131.GI13236@kernel.org>
Date:	Wed, 4 Nov 2015 11:51:31 -0300
From:	Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
To:	Brendan Gregg <brendan.d.gregg@...il.com>
Cc:	Namhyung Kim <namhyung@...nel.org>, 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: [PATCHSET 0/4] perf report: Support folded callchain output (v4)

Em Tue, Nov 03, 2015 at 10:02:32PM -0800, Brendan Gregg escreveu:
> On Tue, Nov 3, 2015 at 5:54 PM, Namhyung Kim <namhyung@...nel.org> wrote:
> > Ah, makes sense.  So it'd look like

> >   $ perf report --stdio -g folded,count,info -F none -s comm
> >   $ perf report --stdio -g folded,count,info -F none -s pid

> > The output would be

> >   809 swapper-0 cpu_bringup_and_idle;cpu_startup_entry;default_idle_call;arch_cpu_idle;default_idle;xen_hypercall_sched_op
 
> Thanks, looks almost right: a couple of minor changes:
 
> 1. If perf already has the precedent of "PID:comm", instead of my
> "comm-PID", then maybe it should use "PID:comm" for perf consistency.
> Doesn't make much difference to me.
> 2. The second space, delimiting "PID:comm" (or comm) and the stack...
> I'm nervous about using space as a delimiter any more than once, since
> it can also appear in comm (eg, "java main") and frames (eg,
> "JavaCalls::call_helper(JavaValue*, methodHandle*, JavaCallArguments*,
> Thread*)" -- that's direct from "perf script"!). I'd consider making
> it a semicolon:
 
> 809 swapper-0;cpu_bringup_and_idle;cpu_startup_entry;...
 
> So the output is "value key", and key is a semicolon delimited stack
> with an optional comm or PID:comm frame at the start.

Agreed, but then, we can have some sort of default and also be able to,
using -F, specify what are the fields we want, and in which order, and I
liked your suggestion of being able to specify "-F none" and that mean
no hist line to be produced.

Likewise, the way that each callchain line should be formatted should be
programmable via the command line, via the -g option, no? Then script
writers could use it in a way that doesn't requires further processing,
as Brendan showed.

But yeah, the value is the semicolon delimited stack all the way to the
comm/PID:comm if there are more than one or if the user asks it to be
there via a -g keyword, all the other counts/info are just relative to
that, CSV or whatever other delimiter the user asks it to, and space is
not an option, as we know it can appear in the middle of a COMM:

[root@zoo ~]# perf report -s comm | grep '[a-zA-Z] [a-zA-Z]'
# To display the perf.data header info, please use
# --header/--header-only options.
# Total Lost Samples: 0
# Samples: 164K of event 'cycles:pp'
# Event count (approx.): 34422160859
     0.11%  DOM Worker     
     0.10%  JS Helper      
     0.01%  Qt bearer threa
     0.00%  Socket Thread  
     0.00%  dconf worker   
     0.00%  JS Watchdog    
[root@zoo ~]#

- Arnaldo
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