Xen overview

Reference: CPU scheduling for virtual desktop infrastructure, Hwanju Kim
Task-aware Virtual Machine Scheduling for I/O Performance, Hwanju Kim, VEE'09
Running Xen, Matthews, Prentice hall

Xen Overview

Xen is an open-source hypervisor based on a paravirtualization technique, which achieves higher performance than full virtualization approaches.
(Full virtualizatoin: allows a system to run many instructions directly on the raw ahrdware. It no longer must use software to simulate a different basic architecture.)

Xen puts the priviledged VM, called domain0, in charge of managing other guest VMs, called domainU.

Xen also supports full virtualization based on hardware-assisted virtualization(Intel-VT and AMD-V), ensuring that it is possible to run unmodified OSes such as Windows. such a full-virtualized domain is called a hardware virtual machine (HVM) by Xen.

The Xen Hypervisor

The Xen hypervisor is the heart of Xen. It sits between the guest domains and the physical hardware.
- allocate and control resources
- enforce protection and isolation
In this chapter, I describe the Xen hypervisor and how it interacts with guest domains.

Xen Hypervisor

The following list summarizes the role of the hypervisor:
1. The hypervisor gives each guest domain a portion of the full physical machine resources.

2.The hypervisor exports simplified devices to guest domains.

3. The hypervisor can modify portions of the physical architecture that are difficult to fully virtualize.