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RE: [Xen-devel] Genapic

Natasha, thanks for bringing order back to the discussion :-)

> The question is where to go from here to enable Xen to run on sub-arch

> machines.  Given the impending move to Xen 3.0, I think it would be 
> best to pull in the needed Linux-i386 genapic code near-term.

I agree that this is the best direction to follow.

> This code may very well not be sufficient for newer x86-64 machines

Yes, I think this is true.

> Personally, I don't know.  I also don't know if the x86-64 code can be

> easily ported to work on the i386 machines currently being targeted.
> If it can then a move to the x86-64 style may be a good move for the 
> future.  Or maybe we need to find a way for both to coexist within

We have a few options for getting both i386 and x86_64 genapics working
in Xen:

1. Merging the two genapic models into one unified model. This will be a
sizeable effort and so is feasible only post Xen 3.0. 

2. Create a x86_64 sub-architecture for i386 genapic. But I am not sure
how much work will be involved or if this is the best direction to

3. Mimic the Linux kernel and have separate genapic models.

> Does this sound like a viable way forward?  Or have I missed
For the moment I think it is best we follow Natasha's suggestion and
work towards bringing in the i386 genapic mode. 



> On Wed, 18 May 2005 17:54:43 +0100, Keir Fraser
> wrote:
> >
> > On 18 May 2005, at 16:45, Puthiyaparambil, Aravindh wrote:
> >
> >> Genapic is done differently for i386 and x86_64 in the LK. In i386
> is
> >> machine specific and in x86_64 it is APIC model specific. Do you
> >> Xen to mimic that? Further more both i386 and x86_64 have separate
> >> apic.c, io_apic.c (just to name a couple) files. Xen shares them
> between
> >> the two. Will that cause any problems?
> >>
> >> I am wondering if it is possible to have a unified genapic for Xen.
> >> is it way too complicated?
> >
> > Shared platform code (apics and the like) has been remarkably
> > This is to be expected:  processor differences aside, i386 and
> > are identical platforms. So, for example, fixing Xen's smpboot.c
> > (derived from Linux/i386) for x86/64 required one or two lines to be
> > changed. Same for ACPI parsing, MP-table parsing, and so on. I
> > why i386 and x86/64 have been allowed to diverge so wildly in Linux?
> >
> >   -- Keir

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