linux-kernel - Re: Human readable output for function return tracer

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Message-ID: <20081124181515.GG26466@ghostprotocols.net>
Date:	Mon, 24 Nov 2008 16:15:15 -0200
From:	Arnaldo Carvalho de Melo <acme@...hat.com>
To:	Frédéric Weisbecker <fweisbec@...il.com>
Cc:	Ingo Molnar <mingo@...e.hu>, Steven Rostedt <rostedt@...dmis.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: Human readable output for function return tracer

Em Mon, Nov 24, 2008 at 03:39:45PM +0100, Frédéric Weisbecker escreveu:
> Hi,
> 
> I'm planning to apply an idea proposed by Ingo to make the output on
> the function return tracer
> more "eyes-parsable".
> The idea consists on a trace which has flow similar to C code:
> 
> func1() {
>     func2() {
>         func3() {
>         }
>     }
>     func4() {
>     }
> }
> 
> (With time of execution added on closing braces).

I do something like that in my ctracer tool[1], take a look at one of
the callgraphs:

http://oops.ghostprotocols.net:81/ostra/dccp/tx/

To save space I the above sequence is represented as:

 func1() {	
     func2() {
         func3()                   1us
     }                             5us
     func4()                       5us
 }                                12us

I.e. the leaf functions doesn't use {}

> The problem is that the traces arrive in the reverse order, according
> to the fact that functions
> are traced on return.
> The order corresponding to the above example would be as the following:
> 
> func3, func2, func4, func1

On ctracer I didn't had this problem as I don't trace all functions,
just the ones that receive as one of its parameters a pointer to the
desired struct, and this pointer is present in all the trace buffer
entries, so as part of postprocessing it separates the callgraphs per
object.

- Arnaldo

[1] git://git.kernel.org/pub/scm/linux/kernel/git/acme/pahole.git
    http://git.kernel.org/?p=linux/kernel/git/acme/pahole.git;a=blob_plain;f=README.ctracer
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