Re: ftrace behaviour (was: [PATCH] ftrace: introduce tracing_reset_online_cpus() helper)

From: Steven Rostedt <rostedt@goodmis.org>
To: Pekka Paalanen <pq@iki.fi>
Cc: "Ingo Molnar" <mingo@elte.hu>,
	"Frédéric Weisbecker" <fweisbec@gmail.com>,
	"Pekka J Enberg" <penberg@cs.helsinki.fi>,
	LKML <linux-kernel@vger.kernel.org>,
	"Markus Metzger" <markus.t.metzger@gmail.com>
Subject: Re: ftrace behaviour (was: [PATCH] ftrace: introduce tracing_reset_online_cpus() helper)
Date: Fri, 19 Dec 2008 20:46:38 -0500 (EST)	[thread overview]
Message-ID: <alpine.DEB.1.10.0812192043320.29275@gandalf.stny.rr.com> (raw)
In-Reply-To: <20081220033822.362bc88a@daedalus.pq.iki.fi>

On Sat, 20 Dec 2008, Pekka Paalanen wrote:

> On Fri, 19 Dec 2008 19:29:30 -0500 (EST)
> Steven Rostedt <rostedt@goodmis.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