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Ian Pratt University of Cambridge and Founder of XenSource Inc.

Xen and the Art of Virtualization. Ian Pratt University of Cambridge and Founder of XenSource Inc. Computer Laboratory. Outline. Virtualization overview Xen Today : 2.0 Overview

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Ian Pratt University of Cambridge and Founder of XenSource Inc.

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  1. Xenand the Art of Virtualization Ian Pratt University of Cambridge and Founder of XenSource Inc. Computer Laboratory

  2. Outline • Virtualization overview • Xen Today : 2.0 Overview • Architecture • Performance • Live VM Relocation • Xen 3.0 Roadmap (Q2 2005)

  3. Virtualization Overview • Single OS image: Ensim, Vservers, CKRM • Group user processes into resource containers • Hard to get strong isolation • Full virtualization: VMware, VirtualPC • Run multiple unmodified guest OSes • Hard to efficiently virtualize x86 • Para-virtualization: UML, Xen • Run multiple guest OSes ported to special arch • Arch Xen/x86 is very close to normal x86

  4. Xen Today : 2.0 Features • Secure isolation between VMs • Resource control and QoS • Only guest kernel needs to be ported • All user-level apps and libraries run unmodified • Linux 2.4/2.6, NetBSD, FreeBSD, Plan9 • Execution performance is close to native • Supports the same hardware as Linux x86 • Live Relocation of VMs between Xen nodes

  5. Para-Virtualization in Xen • Arch xen/x86 : like x86, but replaces privileged instructions with Xen hypercalls • Avoids binary rewriting and fault trapping • For Linux 2.6, only arch-dep files modified • Modify OS to understand virtualised env. • Wall-clock time vs. virtual processor time • Xen provides both types of alarm timer • Expose real resource availability • Enables OS to optimise behaviour • MMU virtualisation: direct vs. shadow mode

  6. I/O Architecture • Xen IO-Spaces delegate guest OSes protected access to specified h/w devices • Virtual PCI configuration space • Virtual interrupts • Devices are virtualised and exported to other VMs via Device Channels • Safe asynchronous shared memory transport • ‘Backend’ drivers export to ‘frontend’ drivers • Net: use normal bridging, routing, iptables • Block: export any blk dev e.g. sda4,loop0,vg3

  7. VM0 VM1 VM2 VM3 Device Manager & Control s/w Unmodified User Software Unmodified User Software Unmodified User Software GuestOS (XenLinux) GuestOS (XenLinux) GuestOS (XenLinux) GuestOS (XenBSD) Back-End Back-End Native Device Driver Native Device Driver Front-End Device Drivers Front-End Device Drivers Virtual CPU Virtual MMU Control IF Safe HW IF Event Channel Xen Virtual Machine Monitor Hardware (SMP, MMU, physical memory, Ethernet, SCSI/IDE) Xen 2.0 Architecture

  8. System Performance 1.1 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0 L X V U L X V U L X V U L X V U SPEC INT2000 (score) Linux build time (s) OSDB-OLTP (tup/s) SPEC WEB99 (score) Benchmark suite running on Linux (L), Xen (X), VMware Workstation (V), and UML (U)

  9. TCP results 1.1 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0 L X V U L X V U L X V U L X V U Tx, MTU 1500 (Mbps) Rx, MTU 1500 (Mbps) Tx, MTU 500 (Mbps) Rx, MTU 500 (Mbps) TCP bandwidth on Linux (L), Xen (X), VMWare Workstation (V), and UML (U)

  10. Scalability 1000 800 600 400 200 0 L X L X L X L X 2 4 8 16 Simultaneous SPEC WEB99 Instances on Linux (L) and Xen(X)

  11. Live VM Relocation • Why is VM relocation useful? • Managing a pool of VMs running on a cluster • Taking nodes down for maintenance • Load balancing VMs across the cluster • Why is it a challenge? • VMs have lots of state • Some VMs will have soft real-time requirements • E.g. web servers, databases, game servers • Can only commit limited resources to migration

  12. Rate Limited Migration

  13. Quake 3 Server migration

  14. Roadmap for Xen 3.0 • SMP guest OSes • Prototype now working, undergoing tuning • Required careful design to get good performance and retain security guarantees • Support for Intel VT-x extensions • Run ‘legacy’ unmodified OSes • Other ports : x86/64 and ia64 (ppc) • Both Xen x86/64 and ia64 now boot!

  15. Roadmap for Xen 3.0 • Better cluster management tools • Manage pool of VMs across a set of nodes • Better tools for QoS control • New GUI management tool • Improved hardware compatibility • Graphics cards, ACPI, APM

  16. Research Roadmap : 4.0 • Cluster load balancing algorithms • Exploit properties of live migration • Software fault tolerance • Exploit deterministic replay • System debugging • Lightweight checkpointing and replay • VM forking • Lightweight service replication, isolation • Secure virtualization • Multi-level secure Xen

  17. Conclusions • Xen is a complete and robust GPL VMM • Outstanding performance and scalability • Excellent resource control and protection • Live relocation makes seamless migration possible for many real-time workloads • http://xensource.com • http://xen.sf.net

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