Date: Sat, 22 Nov 2008 08:30:37 -0500 (EST)
From: Steven Rostedt <rostedt@goodmis.org>
To: Peter Teoh <htmldeveloper@gmail.com>
cc: Steven Rostedt <srostedt@redhat.com>, LKML <linux-kernel@vger.kernel.org>
Subject: Re: Some FTRACE related question
In-Reply-To: <804dabb00811220047q6e0f24eap23e9a7c4c7bd71b6@mail.gmail.com>
Message-ID: <alpine.DEB.1.10.0811220827310.26464@gandalf.stny.rr.com>
References: <804dabb00811220047q6e0f24eap23e9a7c4c7bd71b6@mail.gmail.com>
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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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