linux-kernel - Re: [PATCH v2] ftrace: dump out ftrace buffers to console on panic

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Date:	Fri, 15 Aug 2008 17:40:14 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH v2] ftrace: dump out ftrace buffers to console on panic


* Steven Rostedt <rostedt@...dmis.org> wrote:

> [
>  Changes since -v1:
>   Got alpine to send correctly (as well as spell check working).
>   Removed config option.
>   Moved the static variables into ftrace_dump itself.
>   Gave printk a log level.
> ]
> 
> At OLS I had a lot of interest to be able to have the ftrace buffers 
> dumped on panic.  Usually one would expect to uses kexec and examine 
> the buffers after a new kernel is loaded. But sometimes the resources 
> do not permit kdump and kexec, so having an option to still see the 
> sequence of events up to the crash is very advantageous.
> 
> This patch adds the option to have the ftrace buffers dumped to the 
> console in the latency_trace format on a panic. When the option is 
> set, the default entries per CPU buffer are lowered to 16384, since 
> the writing to the serial (if that is the console) may take an awful 
> long time otherwise.

we had this in the latency tracer - so it's a very useful feature. 
Applied to tip/tracing/ftrace, thanks Steve.

	Ingo
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