linux-kernel - Re: Relicensing tracepoints and markers to Dual LGPL v2.1/GPL v2,headers to Dual BSD/GPL

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Date:	Mon, 26 Oct 2009 21:21:13 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Arjan van de Ven <arjan@...radead.org>
Cc:	Pierre-Marc Fournier <pierre-marc.fournier@...ymtl.ca>,
	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


* Arjan van de Ven <arjan@...radead.org> wrote:

> 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.

That too - plus 'being in the kernel repo' does not mean it has to run 
in kernel mode. It could be a vdso feature or a library in tools/. I'm 
quite sure it's a mistake to ad-hoc export the current tracepoint.c code 
to user-space without having it all under the same maintenance envelope.

	Ingo
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