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[Xen-users] Re: xen on amd64 or intel

Daniel Goertzen <goertzen@xxxxxxxx> writes:

> The virtualization hardware only helps you when you have OSes that are
> not Xen aware.  Since you say you just want to run linux, the
> vanderpool and pacifica extensions will do nothing for you.  Also
> (someone correct me if I'm wrong), Xen aware linux is faster than
> fully virtualized linux.

It depends. In theory SVM(=Pacifica)/VMX can do some things like 
system calls more efficiently. For other things Xen aware is better.

But overall the jury is still out because the implementations of
VMX/SVM are not particularly optimized yet.

Especially the Xen aware drivers are much better than the emulated
device model in the native guests, but there is no reason you couldn't
later use Xen aware driver with an otherwise non Xen aware OS
(but I don't think that works right now) 
So right now Xen aware Linux should be faster in most cases, but 
longer term fully virtualized might catch up and be better for some cses.

> As for 32 bit vs 64 bit kernels, you generally cannot mix both on the
> same physical hardware.  Vanderpool/Pacifica allows you to break this.

I don't think that's fully true for domUs, although you cannot 
mix non PAE and PAE kernels (and 64bit hypervisor implies PAE).

But I would expect this limitation to fall at some point too
so that you could possibly run non PAE Xen aware kernels on 
PAE or 64bit Hypervisors.
For dom0s the domain has to match the hypervisor, same for the 
the admin tools.


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