The upcoming 2.6.20 Linux kernel is bringing a nice virtualization framework for all virtualization fans out there. It's called KVM, short for Kernel-based Virtual Machine. Not only is it user-friendly, but also of high performance and very stable, even though it's not yet officialy released. This article tries to explain how it all works, in theory and practice, together with some simple benchmarks.

A little bit of theory

There are several approaches to virtualization, today. One of them is a so called paravirtualization, where the guest OS must be slightly modified in order to run virtualized. The other method is called "full virtualization", where the guest OS can run as it is, unmodified. It has been said that full virtualization trades performance for compatibility, because it's harder to accomplish good performance without guest OS assisting in the process of virtualization. On the other hand, recent processor developments tend to narrow that gap. Both Intel (VT) and AMD (AMD-V) latest processors have hardware support for virtualization, tending to make paravirtualization not necessary. This is exactly what KVM is all about, by adding virtualization capabilities to a standard Linux kernel, we can enjoy all the fine-tuning work that has gone (and is going) into the kernel, and bring that benefit into a virtualized environment.