Revisit Xen support

[Clint Byrum]

Excerpts from Nathan Stratton Treadway's message of Sat Apr 02 04:14:19 -0700 2011:
> On Fri, Apr 01, 2011 at 16:51:04 -0700, Clint Byrum wrote:
> > Other than people already having familiarity with Xen, what is a
> > compelling reason to support it in favor of, or in addition to, KVM?
> 
> I don't know all the details myself, but my coworkers did some testing
> and found that KVM was not able to isolate the virtual machines properly
> when there was a high IO load.   In the end they switched back to
> running Debian on the Dom0 so we could use Xen.

Nathan, can you dig up any facts to back this up? I understand that you
weren't able to make KVM do what you knew how to do in Xen, but that
doesn't mean that KVM can't, just that the docs and interface are lacking.