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Date:	Mon, 26 Oct 2009 07:18:32 -0700
From:	Arjan van de Ven <arjan@...radead.org>
To:	Pierre-Marc Fournier <pierre-marc.fournier@...ymtl.ca>
Cc:	Ingo Molnar <mingo@...e.hu>, GeunSik Lim <leemgs1@...il.com>,
	Zhaolei <zhaolei@...fujitsu.com>,
	Wu Fengguang <fengguang.wu@...el.com>,
	Jesper Juhl <jj@...osbits.net>,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	Adrian Bunk <bunk@...sta.de>,
	Harvey Harrison <harvey.harrison@...il.com>,
	"Robert P. J. Day" <rpjday@...dspring.com>,
	Jaswinder Singh Rajput <jaswinderrajput@...il.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	linux-kernel@...r.kernel.org,
	Dominique Toupin <dominique.toupin@...csson.com>,
	Michel Dagenais <michel.dagenais@...ymtl.ca>
Subject: Re: Relicensing tracepoints and markers to Dual LGPL v2.1/GPL
 v2,headers to Dual BSD/GPL

On Mon, 26 Oct 2009 09:17:49 -0400
Pierre-Marc Fournier <pierre-marc.fournier@...ymtl.ca> wrote:

> Ingo Molnar wrote:
> > 
> > But i also disagree with it on a technical level: code duplication
> > is _bad_. Why does the code have to be duplicated in user-space
> > like that? I'd like Linux tracing code to be in the kernel repo.
> > Why isnt this done properly, as part of the kernel project - to
> > make sure it all stays in sync?
> > 
> 
> If you mean that this code should solely be used inside the kernel,
> then what you propose technically does not work. There is a very high
> cost to accessing kernel code from userspace. 

yeah 100 cycles is insanely high, that's at least the equivalent of...
say one cache miss.


-- 
Arjan van de Ven 	Intel Open Source Technology Centre
For development, discussion and tips for power savings, 
visit http://www.lesswatts.org
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