Xen an art of virtalization

8/8/2019 Xen an art of virtalization

1/23

Xen and the Art of Virtualization

P. Barham, et. al.

SOSP 2003

Presented by Jae-Wan Jang

([email protected])


2/23

2/23

VMM>Virtual Machine Monitor (VMM)

A software layer which provides virtualized comput ing

environment Not only monitoring VM but also providing and controll ing

environment

HostcomputerHostcomputer

VMM


3/23

3/23

Xen> Targets to x86 architecture

> Type I (Classical system VM)

>Allows direct execution

> Supports unmodified application binaries

> Supports full multi-application operating system

> Goal of Xen

Isolation & low overhead


4/23

4/23

VMM

Difficulties in x86 virtualization>Virtualizable?

All sensitive instructions should be privileged instructions

> x86 architecture has instructions which are sensitive butunprivileged

GuestOS

HardwareHardware

GuestOS

GuestOS

GuestOS


5/23

5/23

Para-virtualization

> Full virtualization overhead

Binary rewrite technique

Identical shadow version of various system states

> Para-virtualization Similar machine abstraction with small modifications (keeping

application-binary interfaces)

Requires guest operating system modifications

Promises better performance than full virtualization


6/23

6/23

Design details

> Overall architecture

> Hypercall & events

> CPU

> Memory

> I/O device


7/23

7/23

Overall architecture

Hardware(hostcomputer)

GuestOS

dom0 domU domU domU

XenoLinux

ControlPlane

Software

User

Software

User

Software

User

Software

XenoLinux XenoBSDXenoBSD

dom0

Control I/F Xen (hypervisor)

VirtualDevices

Virtual DevicesDriver





8/23

8/23

Hypercall & events

> Mechanisms for interaction between Xen and guest OS

> Hypercall

Synchronous calls from guest OS to Xen

Similar concept to system call between process andoperating system

Ex) Page table updates

> Events

Asynchronous notification from Xen to guest OS

Replaces device interrupt delivery


9/23

9/23

CPU

> Protection ring

Ring 0 : Xen VMM

Ring 1 : Guest OS

Ring 3 : User software

ring0

ring3

ring2

ring1 1. Executeprivileged

instructions

2. Generalprotection

fault


10/23

10/23

CPU

> Exception handling

Exceptions including memory faults and system traps

Every exception refers to Xens IDT (interrupt descriptortable)

Registering guest OS IDT w ith Xen

ring0

ring3

ring2

ring1

IDT of VMM

excep t i ons

IDT of Guest OS

IDT of Guest OS

CurrentlyrunningVM


11/23

11/23

CPU

>VM scheduling

Borrowed virtual time (BVT) scheduling algorithm

5 ms time slice used

> Time & Timer

Real t ime TCP/ IP t imeout

Virtual time Scheduling

Alarm t imer for real time and virtual time

Xen

GuestOS


12/23

12/23

Memory

> Kinds of address

Virtualaddress

Physicaladdress

Machineaddress

VM

Host

0

256MB

128MB

384MB


13/23

13/23

Memory

> MMU virtualization : Shadow-mode vs. direct-mode

Virtual Physical

Virtual Machine

MMU

Guest OS

VMM

Hardware

Virtual Machine


14/23

14/23

Memory

> Direct-Mode Xen MMU virtualization

Virtual Machine

GuestreadGuestwrite

Validation Access&dirtybits


15/23

15/23

Memory

> Memory map

ring3

Kernel

User

4GB

3GB

0GB

XenSS

U ring

1

rin

g

0


16/23

16/23

I/ O device virtualization

> I/O rings

For efficient data transfer between Xen and guest OS


17/23

17/23

I/ O device virtualization

> Network

VIF (Virtual network Interface)

VFR (Virtual Firewall Router)

> Disk

VBD (Virtual Block Device)

SCSI disk


18/23

18/23

Evaluation

> Experiment environment

Dell 2650 dual processor 2.4GHz Xeon server w ith 2GB RAM

Linux 2.4.21

> Compared VMMs

(native) Linux

XenoLinux

VMware workstation 3.2

User-Mode Linux


19/23

19/23

Evaluation

> Relative performance


20/23

20/23

Evaluation

> Performance of guest OS


21/23

21/23

Evaluation

> Concurrent VM performance


22/23

22/23

Evaluation

> Scalability


23/23

23/23

Current status

> Direct access to hardware device in driver domain

> SMP guest

> Hardware virtualization technique support (Intel VT, AMDPacifica)

>VM relocation (live migration)

Xen an art of virtalization

Documents

Transcript of Xen an art of virtalization