Heterogeneous Chip Multiprocessor Design for Virtual Machines

Dan Upton and Kim Hazelwood

University of Virginia

Pairing CMPs and VMs

• Challenge for chip multiprocessors: exploiting all available thread-level parallelism

• Challenge for virtual machines: reducing overhead

• Our solution: moving the VM to a separate core – only give a VM core what the VM needs

Heterogeneous Chip Multiprocessors

• Applications have different needs– Ex: Cache performance, available ILP

• Heterogeneous CMPs can be used to meet design constraints– Ex: Size, power, cost

Virtual machines• Many practical applications

– Dynamic translation (legacy ISA support)– Security– Instrumentation– …

HW

OS

App VM

App

HW

VM

OS

App App

Process VMs (Ex: Pin, JVM, Rosetta) System VMs (Ex: Xen, Transmeta)

Design Approach

• Characterize a VM’s microarchitectural performance

• Examine processor organization options• Consider beneficial modifcations for support

SimpleScalar-x86

Pin

Application

Two Examples

• Comparison of branch behavior against benchmarks from SPECINT 2000

• Comparison of cache performance

• Other experiments in paper

Example: Branch Prediction

0

0 . 1

0 . 2

0 . 3

0 . 4

0 . 5

0 . 6

0 . 7

0 . 8

0 . 9

1

P in b z ip 2 c r a f t y g c c g z ip m c f p a r s e r

A p p l i c a t i o n s ( P i n + S P E C I N T 2 0 0 0 )

IPC

(n

orm

ali

ze

d t

o

pe

rfe

ct

bra

nc

h p

red

icti

on

)

B im o d a l O n l y

H a l f - s iz e C o m b in in g

C o m b in in g

Example: L1 CachesP i n L 1 C a c h e P e r f o r m a n c e

0 . 0 0 %

1 . 0 0 %

2 . 0 0 %

3 . 0 0 %

4 . 0 0 %

5 . 0 0 %

6 . 0 0 %

7 . 0 0 %

8 . 0 0 %

D a t a In s t r u c t io n

Mis

s R

ate

6 4 k 4 - w a y 3 2 k 4 - w a y 3 2 k 2 - w a y 1 6 k 2 - w a y 1 6 k d m a p

Example: L2 CacheP i n L 2 C a c h e P e r f o r m a n c e

0 . 0 0 %

1 0 . 0 0 %

2 0 . 0 0 %

3 0 . 0 0 %

4 0 . 0 0 %

5 0 . 0 0 %

6 0 . 0 0 %

7 0 . 0 0 %

5 1 2 k 4 w a y 2 5 6 k 4 w a y 1 2 8 k 4 w a y

Mis

s R

ate

Design Options• Two basic classes:

General Purpose 1

General Purpose 2

VM(other

specialized)

General Purpose

VM

General Purpose

VM

General Purpose

VM

General Purpose

VM

Support Structures

Application CoreVM Core

where to compile

where to resume executingsupport for

indirect branches

• Support for tasks normally handled in software

Related Work

• Hardware support for VMs (Trident, DAISY, Kim and Smith)

• Transmeta

• Java in hardware (picoJava, JOP)

Work in Progress

• Comparing similarity of Pin to other VM software

• Characterizing VM compilation, cache management