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

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Message-ID: <20091210070800.GB16874@elte.hu>
Date:	Thu, 10 Dec 2009 08:08:00 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	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>
Cc:	linux kernel <linux-kernel@...r.kernel.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH 2/4] ftrace - add function_duration tracer

* Tim Bird <tim.bird@...sony.com> wrote:

> Add function duration tracer.
> 
> Signed-off-by: Tim Bird <tim.bird@...sony.com>
> ---
>  kernel/trace/Kconfig          |    8
>  kernel/trace/Makefile         |    1
>  kernel/trace/trace.c          |   32 ++
>  kernel/trace/trace_duration.c |  527 ++++++++++++++++++++++++++++++++++++++++++
>  4 files changed, 568 insertions(+)

Please do it in a cleaner an more generic fashion: add a "function 
event" that perf can see and process, so all the output embellishment 
can be done outside of the kernel, in tools/perf/.

We want to wind down the current maze of ftrace plugins, not extend 
them. We already obsoleted the following ftrace plugins: scheduler, 
sysprof, blktrace, kmem, scheduler, etc. There's more work ongoing and 
broad agreement between folks developing it that this is the way 
forward.

The function tracer / function graph tracer is a holdout due to its 
complexity - but that by no means weakens the argument and the necessity 
to migrate it.

ftrace plugins were a nice idea originally and a clear improvement over 
existing alternatives, but now that we've got a technicaly superior, 
unified event framework that can do what the old plugins did and much 
more, we want to improve that and not look back ...

Thanks,

	ingo
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