Outline Motivation Approaches Xen Architecture Xen Evaluation Xen and the Art of Virtualization P. Barham, B. Dragovic, K. Fraser, S. Hand, T. Harris, A. Ho, R. Neugebauer, I. Pratt, A. Warfield Charalampos S. Nikolaou [email protected]Department of Informatics and Telecommunications January 27, 2008 Charalampos S. Nikolaou Xen and the Art of Virtualization
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OutlineMotivationApproaches
Xen ArchitectureXen Evaluation
Xen and the Art of VirtualizationP. Barham, B. Dragovic, K. Fraser, S. Hand, T. Harris, A. Ho, R.
Charalampos S. Nikolaou Xen and the Art of Virtualization
OutlineMotivationApproaches
Xen ArchitectureXen Evaluation
1 Motivation
2 Approaches
3 Xen Architecture
4 Xen Evaluation
Charalampos S. Nikolaou Xen and the Art of Virtualization
OutlineMotivationApproaches
Xen ArchitectureXen Evaluation
Problems to be tackledSolution
Power Savings
Reduce Costs
Hardware isolation
Legacy operating systems
Testing
Security and performance isolation
Maintenance - Management
Charalampos S. Nikolaou Xen and the Art of Virtualization
OutlineMotivationApproaches
Xen ArchitectureXen Evaluation
Problems to be tackledSolution
The idea
Partition a machine to support concurrent execution of multipleoperating systems in one machine.The approach behind this idea is called Virtualization.In general, virtualization is implemented by a software layerbetween the OS and the hardware providing an abstraction more orless identical to the underlying machine.
Charalampos S. Nikolaou Xen and the Art of Virtualization
OutlineMotivationApproaches
Xen ArchitectureXen Evaluation
Single OS image (x86 architecture)(Full) VirtualizationParavirtualizationChallenges
The most privileged entity is the OS itself.OS provides Users with a hardware abstractionfunctionally identical to the physical hardware.
x86 architecture offers four levelsof privileges known as Ring 0, 1, 2 and 3. Thelevel of Ring determines the degree of privilegethat the current executing instruction has.
User applications run in Ring 3, while the OSruns in Ring 0, because of the need to executeprivileged instructions for accessing/managing the hardware.
User level code is directly executed on theCPU.
Charalampos S. Nikolaou Xen and the Art of Virtualization
OutlineMotivationApproaches
Xen ArchitectureXen Evaluation
Single OS image (x86 architecture)(Full) VirtualizationParavirtualizationChallenges
TraditionalVMM (Virtual Machine Monitor) exposesits hardware as being functionally identicalto the physical hardware (VMware’s approach).
VMM provides eachGuest OS with a virtual BIOS, virtualdevices and virtual memory management.
The GuestOS is not aware it is being virtualized.
VMM translates binary kernel code (onthe fly) into new sequences of instructions that have theintended effect. Code is cached for future use.
User level code is directly executed on theCPU for high performance virtualization.
Sophisticated and difficult approach.
Charalampos S. Nikolaou Xen and the Art of Virtualization
OutlineMotivationApproaches
Xen ArchitectureXen Evaluation
Single OS image (x86 architecture)(Full) VirtualizationParavirtualizationChallenges
VMM exposes a hardwareabstraction that is similar but not identical tothe underlying hardware (Xen’s approach).
The hypervisor(or VMM) provides an interfaceto OS kernel through hypercalls.
Paravirtualization involves modifyingthe OS kernel to replace certain kernelcalls with hypercalls that communicatedirectly with the with the VMM.
The Guest OS have to be modified.There might arrise licence problems.
User level code is directly executed onthe CPU for high performancevirtualization.
Relatively easy approach.Charalampos S. Nikolaou Xen and the Art of Virtualization
OutlineMotivationApproaches
Xen ArchitectureXen Evaluation
Single OS image (x86 architecture)(Full) VirtualizationParavirtualizationChallenges
Challenges to be faced
Virtual machines must be isolated from one another:it is not acceptable for the execution of one running Guest OS(or domain) to adversely affect the performance of another.
Support of a variety of different operating systems.
The performance overhead introduced by virtualization shouldbe small.
Charalampos S. Nikolaou Xen and the Art of Virtualization
The figure depicts the structure of a machine running the Xenhypervisor, hosting a number of different guest operating systems,including Domain0 running control software in a XenoLinuxenvironment.
Charalampos S. Nikolaou Xen and the Art of Virtualization
Data I/O are transferred to and from domains via Xenthrough the use of a buffer descriptor ring.
This is a system that is based around a pair of producerconsumer pointers, one set used within the guest OS, theother within the hypervisor.
This allows for the decoupling of when data arrive/areaccessed and the event notification.
Charalampos S. Nikolaou Xen and the Art of Virtualization
OutlineMotivationApproaches
Xen ArchitectureXen Evaluation
Performance Relative to a Single OS ImageMultitasking/Isolation PerformanceScalabilityConclusions
Charalampos S. Nikolaou Xen and the Art of Virtualization
OutlineMotivationApproaches
Xen ArchitectureXen Evaluation
Performance Relative to a Single OS ImageMultitasking/Isolation PerformanceScalabilityConclusions
Charalampos S. Nikolaou Xen and the Art of Virtualization
OutlineMotivationApproaches
Xen ArchitectureXen Evaluation
Performance Relative to a Single OS ImageMultitasking/Isolation PerformanceScalabilityConclusions
Charalampos S. Nikolaou Xen and the Art of Virtualization
OutlineMotivationApproaches
Xen ArchitectureXen Evaluation
Performance Relative to a Single OS ImageMultitasking/Isolation PerformanceScalabilityConclusions
Conclusions
Xen’s paravirtualization approach:
has great performance (comparable to a native single OSsystem),
is highly scalable, BUT
requires OS’s kernel source modification which due to licencesmight be impossible!
VMware in cooperation with XenSource have proposed an interfacewhich every OS that would like to be virtualized must adhere to.Paravirtualization seems to be the winner!
Charalampos S. Nikolaou Xen and the Art of Virtualization
OutlineMotivationApproaches
Xen ArchitectureXen Evaluation
Performance Relative to a Single OS ImageMultitasking/Isolation PerformanceScalabilityConclusions
References
P. Barham, B. Dragovic, K. Fraser, S. Hand, T. Harris, A. Ho,R. Neugebauer, I. Pratt, and A. Warfield,Xen and the Art of Virtualization, Proc. ACM-SOSP 2003.
VMWare White Paper,Understanding Full Virtualization, Paravirtualization, andHardware Assist.
The LaTeX Beamer Class Homepage.http: // latex-beamer. sourceforge. net/ .
Charalampos S. Nikolaou Xen and the Art of Virtualization