linux-kernel - Re: Some FTRACE related question

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Message-ID: <alpine.DEB.1.10.0811220827310.26464@gandalf.stny.rr.com>
Date:	Sat, 22 Nov 2008 08:30:37 -0500 (EST)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Peter Teoh <htmldeveloper@...il.com>
cc:	Steven Rostedt <srostedt@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: Some FTRACE related question

On Sat, 22 Nov 2008, Peter Teoh wrote:

> Q1:   how to use ftrace to ftrace itself?   (i would like to see some
> ftrace-triggered flow)   In view of the following patch:

ftrace can be very dangerous, (the function tracer part of ftrace).
It would be very difficult for ftrace to ftrace itself.
When I need to debug ftrace, I use my old tracer logdev:

 http://rostedt.homelinux.com/logdev

> 
> http://linux.derkeiler.com/Mailing-Lists/Kernel/2008-11/msg03745.html
> 
> Is it to prevent this from being possible?
> 
> Q2:   how to ftrace s2ram and resume?   I attempted to do it, but the
> trace output is always filled with "resume" related functions when it
> started up, which is only logical.

s2ram does a lot of nasty tricks. On startup, it calls functions before 
smp_prossor_id() is defined. We use that to disable ftrace recursion (see 
Q1 ;-).  But if you use that in s2ram resume, it will blow up.

Now, you can try to hack ftrace for your own tracing to handle the above 
problems.

-- Steve

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