The new Linux kernel 2.6.20 is particularly important for virtualization, officially adopting a virtualization solution, Kernel -based Virtual Machne or KVM (32 and 64bits) as well as support for para-virtualization (only 32bits). (KVM itself is about to support para-virtualization)
Xen project founder and chief architect, Ian Pratt, expressed severe critics about KVM, as reported by DevX News:
Xen is a true hypervisor, whereas KVM is a legacy virtualization solution akin to VMware Workstation, VMserver and Microsoft Virtual PC
It lacks the benefits of para-virtualization performance enhancements that have been pioneered by Xen and are now being copied by VMware and Microsoft.
After seeking for long time inclusion in Linux kernel, Xen founder now snub the opportunity:
The Xen hypervisor is an operating system independent hypervisor that supports many different operating systems (Windows, Solaris, Netware, FreeBSD, OpenBSD, NetBSD) of which Linux is just one (though an important one)
Putting Xen into Linux doesn’t make sense: hypervisors are different beasts from operating systems, so they share little code.