Subject: Re: [PATCH 2/4] ftrace - add function_duration tracer
From: Steven Rostedt <rostedt@goodmis.org>
Reply-To: rostedt@goodmis.org
To: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>, Tim Bird <tim.bird@am.sony.com>,
       Andrew Morton <akpm@linux-foundation.org>,
       Peter Zijlstra <a.p.zijlstra@chello.nl>,
       Arnaldo Carvalho de Melo <acme@redhat.com>,
       Li Zefan <lizf@cn.fujitsu.com>, Thomas Gleixner <tglx@linutronix.de>,
       linux kernel <linux-kernel@vger.kernel.org>
In-Reply-To: <20091210120332.GA5042@nowhere>
References: <4B202778.4030801@am.sony.com> <20091210070800.GB16874@elte.hu>
	 <20091210120332.GA5042@nowhere>
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Organization: Kihon Technologies Inc.
Date: Thu, 10 Dec 2009 09:29:27 -0500
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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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