Xen Overview for
Campus Grids
Andrew Warfield
University of Cambridge
andrew.warfield@cl.cam.ac.uk
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
Consolidate under-utilized servers
to reduce CapEx and OpEx
Avoid downtime with VM Relocation
Dynamically re-balance workload
to guarantee application SLAs
Enforce security policy
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
AGP
ACPI
PCI
32/64bit
VM0
Device
Manager &
Control s/w
VM1
Unmodified
User
Software
VM2
Unmodified
User
Software
GuestOS
GuestOS
GuestOS
(XenLinux)
(XenLinux)
(XenLinux)
Back-End
Back-End
SMP
Native
Device
Driver
Control IF
Native
Device
Driver
Safe HW IF
Front-End
Device Drivers
Event Channel
Virtual CPU
VM3
Unmodified
User
Software
Unmodified
GuestOS
(WinXP))
Front-End
Device Drivers
Virtual MMU
Xen Virtual Machine Monitor
Hardware (SMP, MMU, physical memory, Ethernet, SCSI/IDE)
VT-x
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
SPEC INT2000 (score)
L
X
V
U
Linux build time (s)
L
X
V
U
OSDB-OLTP (tup/s)
L
X
V
U
SPEC WEB99 (score)
Benchmark suite running on Linux (L), Xen (X), VMware Workstation (V), and UML (U)
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
Tx, MTU 1500 (Mbps)
L
X
V
U
Rx, MTU 1500 (Mbps)
L
X
V
U
Tx, MTU 500 (Mbps)
L
X
V
U
Rx, MTU 500 (Mbps)
TCP bandwidth on Linux (L), Xen (X), VMWare Workstation (V), and UML (U)
Scalability
1000
800
600
400
200
0
L
X
2
L
X
4
L
X
8
L
X
16
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
Operating System and Systems Management
Hardware Systems
Acquired by
Platforms & I/O
* Logos are registered trademarks of their owners
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
http://www.cl.cam.ac.uk/Research/SRG/netos/xen/
(Google for “Xen”)