Variar la luminosidad de lamparas

Xen and the Art of Virtualization
Paul Barham∗, Boris Dragovic, Keir Fraser, Steven Hand, Tim Harris, Alex Ho, Rolf Neugebauer†, Ian Pratt, Andrew Warfield
University of Cambridge Computer Laboratory 15 JJ Thomson Avenue, Cambridge, UK, CB3 0FD
{firstname.lastname}@cl.cam.ac.uk

ABSTRACT
Numerous systems have been designed which use virtualization to subdivide the ample resources of a moderncomputer. Some require specialized hardware, or cannot support commodity operating systems. Some target 100% binary compatibility at the expense of performance. Others sacrifice security or functionality for speed. Few offer resource isolation or performance guarantees; most provide only best-effort provisioning, risking denial of service. This paper presents Xen, an x86 virtual machine monitorwhich allows multiple commodity operating systems to share conventional hardware in a safe and resource managed fashion, but without sacrificing either performance or functionality. This is achieved by providing an idealized virtual machine abstraction to which operating systems such as Linux, BSD and Windows XP, can be ported with minimal effort. Our design is targeted at hosting up to 100 virtualmachine instances simultaneously on a modern server. The virtualization approach taken by Xen is extremely efficient: we allow operating systems such as Linux and Windows XP to be hosted simultaneously for a negligible performance overhead — at most a few percent compared with the unvirtualized case. We considerably outperform competing commercial and freely available solutions in a range ofmicrobenchmarks and system-wide tests.

1.

INTRODUCTION

Categories and Subject Descriptors
D.4.1 [Operating Systems]: Process Management; D.4.2 [Operating Systems]: Storage Management; D.4.8 [Operating Systems]: Performance

General Terms
Design, Measurement, Performance

Keywords
Virtual Machine Monitors, Hypervisors, Paravirtualization
∗ †

Microsoft Research Cambridge, UK IntelResearch Cambridge, UK

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Modern computers are sufficiently powerful to use virtualization to present the illusion of many smaller virtual machines (VMs), each running a separate operating system instance. This has led to a resurgence of interest in VM technology. In this paper wepresent Xen, a high performance resource-managed virtual machine monitor (VMM) which enables applications such as server consolidation [42, 8], co-located hosting facilities [14], distributed web services [43], secure computing platforms [12, 16] and application mobility [26, 37]. Successful partitioning of a machine to support the concurrent execution of multiple operating systems poses severalchallenges. Firstly, virtual machines must be isolated from one another: it is not acceptable for the execution of one to adversely affect the performance of another. This is particularly true when virtual machines are owned by mutually untrusting users. Secondly, it is necessary to support a variety of different operating systems to accommodate the heterogeneity of popular applications. Thirdly, theperformance overhead introduced by virtualization should be small. Xen hosts commodity operating systems, albeit with some source modifications. The prototype described and evaluated in this paper can support multiple concurrent instances of our XenoLinux guest operating system; each instance exports an application binary interface identical to a non-virtualized Linux 2.4. Our port of Windows XP...