linux-kernel - Re: [PATCH 2/4] ftrace - add function

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Message-ID: <1260455367.2146.143.camel@gandalf.stny.rr.com>
Date:	Thu, 10 Dec 2009 09:29:27 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Ingo Molnar <mingo@...e.hu>, Tim Bird <tim.bird@...sony.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Li Zefan <lizf@...fujitsu.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/4] ftrace - add function_duration tracer

On Thu, 2009-12-10 at 13:03 +0100, Frederic Weisbecker wrote:

> This makes me feel I'm going to try converting the function graph tracer
> into an event during the next cycle. It does not mean I could make it
> usable as a perf event right away in the same shot that said, as you can
> guess this is not a trivial plug. The current perf fast path is not yet
> adapted for that.

I curious how you plan on doing this. The current event system shows one
event per trace point. A straight forward approach would make every
entry and exit of a function a trace point and that would lead to a very
large kernel to handle that.

Perhaps we could abstract out all entries and exits. We need to be able
to link to a single point (entry or exit) not all.  This also has the
added issue of using the ftrace infrastructure of nop the mcount call.
We also need a way to enable a set of functions.

We may be able to abstract this out, but I'm hesitant on making this the
only interface.

-- Steve

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