Xen Overview for Campus Grids Andrew Warfield University of Cambridge Computer Laboratory

What is hardware virtualization?  Indirect the underlying hardware layer  Allow multiplexing and isolation  Key points:  Treat OS as a component  Split the administrative role in half

What is Xen?  Virtual machine manager (VMM)  Developed at University of Cambridge  An Isolation Kernel  Recently included in mainline Linux  Used in many production environments

Virtualization in the Enterprise X Consolidate under-utilized servers to reduce CapEx and OpEx Avoid downtime with VM Relocation Dynamically re-balance workload to guarantee application SLAs X Enforce security policy X

Why Xen is interesting for Grid/E-Science Environments  Encapsulation OS as management primitive, and strong isolation  Accounting Collect detailed usage data on each VM  Pre-emption and Checkpointing Using suspend/resume  Load Balancing Using migration  Storage virtualization Simple virtual block interface can be mapped to whatever you like (disk/file/etc…)

Virtualization Overview  Single OS image: Virtuozo, Vservers, Zones  Group user processes into resource containers  Hard to get strong isolation  Full virtualization: VMware, VirtualPC, QEMU  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

Paravirtualization  Virtualization is traditionally slow relative to raw hardware (IBM VM, VMware, etc)  Xen paravirtualizes  Co-design with VM OS  Optimize OS to run in a virtualized environment  Maintain ABI – applications stay the same.

Xen 3.0 Architecture Event Channel Virtual MMUVirtual CPU Control IF Hardware (SMP, MMU, physical memory, Ethernet, SCSI/IDE) Native Device Driver GuestOS (XenLinux) Device Manager & Control s/w VM0 Native Device Driver GuestOS (XenLinux) Unmodified User Software VM1 Front-End Device Drivers GuestOS (XenLinux) Unmodified User Software VM2 Front-End Device Drivers Unmodified GuestOS (WinXP)) Unmodified User Software VM3 Safe HW IF Xen Virtual Machine Monitor Back-End VT-x 32/64bit AGP ACPI PCI SMP

System Performance LXVU SPEC INT2000 (score) LXVU Linux build time (s) LXVU OSDB-OLTP (tup/s) LXVU SPEC WEB99 (score) Benchmark suite running on Linux (L), Xen (X), VMware Workstation (V), and UML (U)

TCP results LXVU Tx, MTU 1500 (Mbps) LXVU Rx, MTU 1500 (Mbps) LXVU Tx, MTU 500 (Mbps) LXVU Rx, MTU 500 (Mbps) TCP bandwidth on Linux (L), Xen (X), VMWare Workstation (V), and UML (U)

Scalability LX 2 LX 4 LX 8 LX Simultaneous SPEC WEB99 Instances on Linux (L) and Xen(X)

Web Server Relocation

Performance issues for GRID environments  One problematic workload: Synchronous, low-latency, MPI-style communications.  Domain crossings / no batching.  BUT: Hardware vendors know this is a problem that needs fixing.  Several vendors are in the process of building virtualization-friendly devices.

Existing GRID Users  Tim Freeman and Kate Keahey at Argonne National Lab in Chicago  Looking at combining virtualization with GRID  Environment creation, management, etc.

Other Xen Supporters Hardware Systems Platforms & I/O Operating System and Systems Management * Logos are registered trademarks of their owners Acquired by

Ongoing Work  Parallax: Distributed VM storage  Decentralized, data replication, copy-on-write  Pervasive Debugging  VMs are an ideal debugging environment  XenSE: Security Enhanced Xen  MAC-based VMM

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 (Google for “Xen”)