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Zen and the Art of Virtualization

Zen and the Art of Virtualization. Paul Barham, et al. University of Cambridge, Microsoft Research Cambridge. Published by ACM SOSP’03. Presented by Tina Swenson CS533 – March 5, 2007. Brief History of Virtualization. 1960s IBM System/360 Model 67 Mainframe

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Zen and the Art of Virtualization

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  1. Zen and the Art of Virtualization Paul Barham, et al. University of Cambridge, Microsoft Research Cambridge Published by ACMSOSP’03 Presented by Tina SwensonCS533 – March 5, 2007

  2. Brief History of Virtualization • 1960s IBM System/360 Model 67 Mainframe • Term Hypervisor born out of Supervisor. • Full Virtualization (Disco) • Unmodified OS/application code • Performance hit because hypervisor mediation.x86 architecture problems. • Paravirtualization (Xen) • OS cooperates with hypervisor. • OS code must be modified for this cooperation.

  3. About Xen • A high-performance, resource-managed x86 virtual machine monitor (VMM). • 100 guest OS instances running industry standard apps and services. • The hypervisor (VMM) sitting just above the hardware at a higher privilege mode than the OSes.

  4. Virtual Machine Interface • Memory Management • Guest OSes are responsible for the hardware page tables. • Xen exists in the top section of every address space. • Avoids a TLB flush when entering and leaving the hypervisor. • Disco maintains shadow page tables to handle TLB misses and remain invisible.

  5. Virtual Machine Interface • CPU • The OS is no longer at the most privileged level of the system. • Hypervisor in Ring 0. OS in Ring 1. App code in Ring 3. • Privileged instructions must be validated and executed within Xen. • Disco vs Xen • x86 exceptions map to Xen exception handling tables.

  6. Virtual Machine Interface • Device IO • Device abstractions provided. • IO data moves between domains via shared memory and asynchronous buffer-descriptor rings.

  7. Control Transfer • Hypercall • Synchronous trap by domain into hypervisor to perform a privileged op. • Events • Asynchronous events, replaces device interrupts.

  8. IO Data Transfer • Circular queue of descriptors • Allocated by a domain, accessible by Xen. • Producer-Consumer

  9. Subsystem Virtualization • CPU Scheduling • Domains scheduled via Borrowed Virtual Time. • Virtual Address Translation • Xen registers guest OS page tables with the MMU and allows the Guest OS read-only access. Xen performs page table updates. • No shadow page tables, as with Disco. • Physical Memory • Statically partitioned between domains. • Mapping physical to hardware addresses is up to Guest OS. • Balloon driver – Pages passed between Xen and XenoLinux. • Other • Time and Timers • Network • Disk

  10. Performance • Linux L VMware Workstation VXenoLinux X User-Mode Linux U

  11. Performance • Linux L VMware Workstation VXenoLinux X User-Mode Linux U

  12. Performance • Linux L VMware Workstation VXenoLinux X User-Mode Linux U

  13. Concurrent VM • Linux vs XenoLinux

  14. More Evaluation • Performance Isolation • 4 VMs. 2 normal, 2 nasty • Scalability • Can Xen run 100 domains?

  15. Xen Today • Active Project • University of Cambridge • SourceForge • In Industry • IBM, HP, Intel, Red Hat, AMD and Novell • XenSource

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