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RE: [Xen-devel] Hypercall interface changes for PAE

To: "Gerd Knorr" <kraxel@xxxxxxx>
Subject: RE: [Xen-devel] Hypercall interface changes for PAE
From: "Ian Pratt" <m+Ian.Pratt@xxxxxxxxxxxx>
Date: Wed, 1 Jun 2005 10:30:52 +0100
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Thread-topic: [Xen-devel] Hypercall interface changes for PAE
> I don't thing the performance argument is that important for 
> the xen tools though.  Booting or migrating a domain is a 
> rare event (when compared to the page table manipulations the 
> xen kernel has to do all the time).
> > The only way it can reasonably be done cleanly and with decent 
> > performance is double compilation of the relevant mm 
> functions in Xen 
> > (and libxc too). In which case, having separate hypercall vectors 
> > makes most sense.
> Well, I'd try to get away without double compilation for libxc.
> But you guys know that part of the code much better than I 
> do, so if you think double compilation is the best way to 
> deal with it, lets take that route.

The inner most guts of the domain builder where we build the pagetables,
it's probably best to have two totally separate functions as there are
significant differences between the PAE and non PAE initial pagetables.

For the save/restore functions I'd like to share the source code.
However, it would be very ugly indeed to butcher the code such that the
same compiled code can run-time switch. I think the best soloution is
just to run it through the compiler twice with different header files.
[Aside: we need to give the save/restore code the same treatment that
the improved pte typing patch gave to Xen.] 


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