linux-kernel - Re: [PATCH 2/2] tracing/function-graph-tracer: improve duration output

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Date:	Wed, 3 Dec 2008 16:44:52 +0100
From:	"Frédéric Weisbecker" <fweisbec@...il.com>
To:	"Steven Rostedt" <rostedt@...dmis.org>
Cc:	"Ingo Molnar" <mingo@...e.hu>, "Tim Bird" <tim.bird@...sony.com>,
	"Peter Zijlstra" <a.p.zijlstra@...llo.nl>,
	"Linux Kernel" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] tracing/function-graph-tracer: improve duration output

2008/12/3 Steven Rostedt <rostedt@...dmis.org>:
>
> On Wed, 3 Dec 2008, Fr?d?ric Weisbecker wrote:
>>
>>
>> I proposed a solution for ftrace_printk (which I planned to implement
>> this evening).
>> Since we are in a C-style output, that would be good  to put the ftrace_printk
>> as /* C comments */ inside just below the function that called it.
>> Like this:
>>
>> func_that_called_ftrace_printk {
>>     /* Message from ftrace_printk */
>> }
>>
>> This way we keep the idea of comment which comes along the role of
>> ftrace_printk and we know
>> which function called it, at which depth.....
>>
>> Do you like it this way?
>
> Yes definitely. I thought we already decided to do it that way ;-)


A proposition about this. I want to use __ftrace_printk, make it
generic for both function tracers and have a way to store the current
depth.
One solution: changing the print_entry to have the ip available for
function-tracer and depth available for return-function_tracer.

struct print_entry {
	struct trace_entry	ent;
        union {
	    unsigned long	ip;
            unsigned long       depth;
        } from;
	char			buf[];
};

We could make __ftrace_printk verify which tracer is running.

If normal tracer then
     trace_vprintk(__builtin_return_address(0), .....)
else if graph-tracer
     trace_vprintk(current->curr_ret_stack, ......)

This way we can even forget the ip argument of __trace_printk.
I prefer to ask before changing an exported symbol API....
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