linux-kernel - Re: [ANNOUNCE] New utility: 'trace'

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Message-ID: <20101117182859.GB5352@nowhere>
Date:	Wed, 17 Nov 2010 19:29:02 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Ted Ts'o <tytso@....edu>
Cc:	Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...e.hu>,
	Darren Hart <dvhart@...ux.intel.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Arjan van de Ven <arjan@...radead.org>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Tom Zanussi <tzanussi@...il.com>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Li Zefan <lizf@...fujitsu.com>,
	Jason Baron <jbaron@...hat.com>,
	"David S. Miller" <davem@...emloft.net>,
	Christoph Hellwig <hch@....de>,
	Pekka Enberg <penberg@...nel.org>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	Eric Dumazet <eric.dumazet@...il.com>
Subject: Re: [ANNOUNCE] New utility: 'trace'

On Wed, Nov 17, 2010 at 01:13:40PM -0500, Ted Ts'o wrote:
> On Wed, Nov 17, 2010 at 03:10:33PM +0100, Frederic Weisbecker wrote:
> > Yeah I have a strange workflow. I'm working on that CPU isolation thing
> > and I have dozens of trace_printk all over the place for tons of
> > things. And everytime I remove one to unwind some output or to focus
> > on another one, I often have to restore it later because I need it
> > again. Usually I even just comment it out instead of removing it.
> 
> What I do for my file system development work is to drop in
> trace_printk's everywhere, since they are lightweight and don't slow
> down the system much.  Then when the system wedges, I use sysrq-z to
> get a "flight data recorder" printout of what happened up til the
> system hung.
> 
> I love the fact that the ring buffer is in "overwrite" mode (aka
> flight data recorder mode), and hope this doesn't go away.
> 
> Per line filtering is also great, but very often when I'm interacting
> with the block I/O layer, if something screws up, what happens is "and
> then whole machine locks up", and sysrq-z is literally all I have. 

Yeah all agreed.

Steve proposed to keep the current trace_printk() implementation that relies
on ftrace but rename in into ftrace_printk(). So that we can develop a new
trace_printk() based on trace_event interface and in the meantime keep the
old version in case something messes up with the new thing.

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