Status Report

1
Status Report

• Ian Pratt
• University of Cambridge and Founder of XenSource
  Inc.

Computer Laboratory
2
Overview

• Xen Today 2.0.5
• Xen 3.0 Development Update
• New benchmark results
• Ongoing research

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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

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Para-Virtualization in Xen

• Arch xen_x86 like x86, but replace 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

5
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

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Xen 2.0 Architecture
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Xen 3.0 Architecture
VM3
VM0
VM1
VM2
Device Manager Control s/w
Unmodified User Software
Unmodified User Software
Unmodified User Software
GuestOS (XenLinux)
GuestOS (XenLinux)
GuestOS (XenLinux)
Unmodified GuestOS (WinXP))
AGP ACPI PCI
Back-End
Back-End
SMP
Native Device Driver
Native Device Driver
Front-End Device Drivers
Front-End Device Drivers
VT-x
Event Channel
Virtual MMU
Virtual CPU
Control IF
Safe HW IF
32/64bit
Xen Virtual Machine Monitor
Hardware (SMP, MMU, physical memory, Ethernet,
SCSI/IDE)
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3.0 Headline Features

• AGP/DRM in dom0
• ACPI/PCI support in dom0
• Support for SMP guests
• x86_64 support
• Intel VT-x support for unmodified guests
• Enhanced control and management tools
• Optimised inter-VM networking
• IA64 and Power support, PAE36

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x86_64

• AMD Opteron and Intel EM64T
• Requires different approach to plain x86
• Cant use segmentation to protect Xen from guest
  OS kernels
• Switch page tables between kernel and user
• Large VA space offers other optimisations
• Current design supports up to 8TB mem
• Call for user testing in 2-3 weeks

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SMP Guest OSes

• Takes great care to get good performance while
  remaining secure
• Paravirtualized approach yields many benefits
• Avoids many virtual IPMIs
• Need for better SMP-aware scheduler
• Believed stable, optimisations pending

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VT-x / Pacifica

• Enables unmodified GuestOSes to be supported
• Xen has excellent Shadow page table support
• Requires simple platform emulation
• Install paravirtualized drivers after booting for
  high-performance IO

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4th Generation Tools

• Controlling Xen is easy, its coordinating the
  rest of the system thats hard
• Driver domains firewall/routeing rules shaping
• LVM / filesystem image management
• VM relocation
• Resource measurement, control
• Managing clusters of Xen nodes
• Replace monolithic xend with tool suite
  communicating via The Registry

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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

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VM Relocation Strategy
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Writeable Working Set
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Rate Limited Migration
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Iterative Progress SPECWeb
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Iterative Progress Quake3
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Quake 3 Server migration
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Research Roadmap

• Cluster load balancing
• Pre-migration analysis phase
• Optimization over coarse timescales
• Evacuating nodes for maintenance
• Move easy to migrate VMs first
• Storage-system support for VM clusters
• Decentralized, data replication, copy-on-write
• Internet Suspend Resume
• Just rsync plus IPSec tunnels

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Research Roadmap

• Cluster load balancing algorithms
• Exploit properties of live migration
• System debugging and fault tolerance
• Lightweight checkpointing, distributed
  watchpoints, deterministic replay
• I/O interposition and replay
• VM forking
• Lightweight service replication, isolation
• Secure virtualization
• Multi-level secure Xen

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Conclusions

• Xen 3.0 release on-target!