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Xen and the art of virtualization

Learn about Xen, a high-performance virtual machine monitor that uses para-virtualization to run up to 100 virtual machine instances. This presentation covers the structure, virtual machine interface, control transfer, evaluation, and conclusion of Xen.

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Xen and the art of virtualization

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  1. Xen and the art of virtualization Paul Barham, Boris Dragovic, Keir Fraser, Steven Hand, Tim Harris, Alex Ho, Rolf Neugebauer, lan Pratt, Andrew Warfield Presented by NagaJyothiMurala

  2. Outline • About Xen • Structure • Virtual Machine Interface • Control Transfer • Evaluation • Conclusion

  3. About Xen High performance virtual machine monitor

  4. About Xen • Runs on x86 processors • Lies above hardware • More privileged than OS • Uses Para virtualization • Goal: Up to 100 VM instances

  5. Terminology • Guest OS: OS that Xen can host • Domain: VM within which guest OS executes • Hypervisor: Xen

  6. Structure of machine

  7. Virtual machine interface

  8. Virtual machine interface • Memory management • CPU • Device I/O

  9. Memory management • Most difficult part • Page tables • Guest OS manages hardware page tables • Xen exists in a 64MB section at the top of every address space • Segmentation • Similar to page tables • Segment descriptor's must have lower privilege than Xen • No access to Xen reserved portion of the address space • Physical memory • XenoLinux’s balloon driver

  10. CPU • Privileges • x86 supports 4 privilege levels ( 0 highest.. 3 lowest) • Xen runs in ring 0, OS in ring 1 and applications in ring 3 • Exceptions • Table contains type of exception and handlers identical to x86 hardware • Page fault handler handled differently • Scheduling • Uses Borrowed virtual Time (BVT) scheduling algorithm

  11. Device I/O • Device abstractions • Shared memory, asynchronous buffer descriptor rings • Network • Abstraction of Virtual firewall router (VFR) • Domain’s network interface (VIF) • Two I/O rings of buffer descriptors (for transmit and receive) and rules (<pattern>,<action>) • Round-robin packet scheduler • Disk • Domain0 direct access • All others via virtual block device (VBD) abstractions

  12. I/O Rings Used for data transfer between Xen and guest OSes Circular queue of descriptors Reference to I/O buffers Allocated by domains

  13. Control Transfer • Domains interact with Xen through hypercall • Synchronous software trap • Xen respond to domain using event mechanisms • Asynchronous event mechanism Domain Hypercall Asynchronous Event mechanism Xen

  14. Evaluation • Relative performance • Compared performance of three virtualization techniques with Native Linux • Concurrent virtual machines • Compared performance of Xen with Native Linux • Compared performance of Xen by increasing number of OS instances

  15. Relative Performance

  16. Concurrent Virtual MachinesLinux vsXenoLinux

  17. Conclusion • Architectures such as x86 does not support full virtualization • Xen is a high performance virtual machine monitor which uses Para virtualization • Modification to the kernel code of guest OS is required • Performance achievement near to that of Native Linux

  18. Questions???

  19. References • Graphics taken from previous presentations • “Xen and the art of virtualization”, P. Barham, B. Dragovic, K. Fraser, S. Hand, T. Harris, A. Ho, R. Neugebauer, I. Pratt, and A. Warfield, Proceedings of the 19th Symposium on Operating System Principles, October, 2003. • www.xen.org • http://www.cl.cam.ac.uk/research/srg/netos/papers/2004-xen-ols.pdf

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