linux-kernel - Re: ftrace behaviour (was: [PATCH] ftrace: introduce tracing_reset_online

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Message-ID: <alpine.DEB.1.10.0812192043320.29275@gandalf.stny.rr.com>
Date:	Fri, 19 Dec 2008 20:46:38 -0500 (EST)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Pekka Paalanen <pq@....fi>
cc:	Ingo Molnar <mingo@...e.hu>,
	Frédéric Weisbecker <fweisbec@...il.com>,
	Pekka J Enberg <penberg@...helsinki.fi>,
	LKML <linux-kernel@...r.kernel.org>,
	Markus Metzger <markus.t.metzger@...il.com>
Subject: Re: ftrace behaviour (was: [PATCH] ftrace: introduce
 tracing_reset_online_cpus() helper)


On Sat, 20 Dec 2008, Pekka Paalanen wrote:

> On Fri, 19 Dec 2008 19:29:30 -0500 (EST)
> Steven Rostedt <rostedt@...dmis.org> wrote:
> 
> I thought this was just about not having to do
> 
> $ echo 0 > tracing_enabled
> $ echo 28764243 > buffer_size
> $ echo 1 > tracing_enabled
> 
> and instead just do
> 
> $ echo 28764243 > buffer_size
> 
> which would do exactly the same, except being easier for the user.
> Personally I've never dreamed of any kind of resize-in-flight.
> 

To implement this at the ftrace level should be a trivial change. I'm just 
saying that doing this at the "ring buffer" level might be a bit more 
complex. The ring buffer has no idea of ftrace. It should not. It is at 
a lower lever than ftrace. Although, I do think some of the protecting 
that is done at the tracing level during resize should be moved down into 
the ring buffer layer.

-- Steve

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