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

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Date:	Fri, 19 Dec 2008 23:57:17 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Pekka Paalanen <pq@....fi>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	Frédéric Weisbecker <fweisbec@...il.com>,
	Pekka J Enberg <penberg@...helsinki.fi>,
	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)


* Pekka Paalanen <pq@....fi> wrote:

> > I'm actually against the idea of reseting a trace everytime we enable it.
> > That is:
> > 
> > echo 1 > /debug/tracing/tracing_enabled
> > 
> > This should not reset the tracer. I actually do tracing where I disable 
> > and enable it around areas I am interested in. I want all tracing, not 
> > just the last one.
> 
> But doesn't this go against the fact, that you need to write 0 there to 
> be able to change the ring buffer size?

hm, that ftrace behavior is silly. Steve, i think i mentioned this a long 
time ago and i thought it got fixed? Changing the ring buffer size is a 
slow op, it should include an implicit reset and should be plug-and-play 
with no dependencies of having to stop the trace or something.

	Ingo
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