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 NagaJyothi Murala

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 (, ) 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 Xen Hypercall Asynchronous Event mechanism

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 Machines Linux vs XenoLinux

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