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

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Date:	Thu, 5 Nov 2015 00:34:57 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
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: [PATCHSET 0/4] perf report: Support folded callchain output (v4)

Hi Arnaldo and Brendan,

On Wed, Nov 04, 2015 at 11:51:31AM -0300, Arnaldo Carvalho de Melo wrote:
> 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.

Right.  Actually I'd like to write it that way.. ;-)


> > 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:

Fair enough.


>  
> > 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.

Right.  So '-s <key1>[,<key2>,...] -g info' can control which info is
displayed along with the callchains.

  $ perf report -s comm,dso -g folded,count,info -F none
  809 swapper;[kernel.vmlinux];cpu_bringup_and_idle;cpu_startup_entry;...

Note that the info part (swapper;[kernel.vmlinux]) is also separated
by a semicolon.  But I think it's ok since it's controlled by command
line, so script can know how many entries will be.


> 
> 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:

Yes, I think that we should use a given separator (using -t option)
instead of hard-coded semicolon.  Although it'd be rare, it seems
possible to use semicolons in the comm name too.

Thanks,
Namhyung


> 
> [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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