Re: Relicensing tracepoints and markers to Dual LGPL v2.1/GPLv2,headers to Dual BSD/GPL

[Ingo Molnar]

* Arjan van de Ven <arjan@xxxxxxxxxxxxx> wrote:

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