Parallel Computer Architecture

558

CHAPTER

8

Directory-Based Cache Coherence

8-1 SCALABLE CACHE COHERENCE

This section briefly lays

out the

major organizational alternatives

for

providing

coherent replication

in a

multiprocessor's extended memory hierarchy

and

intro-

duces

the

basic mechanisms that

any

approach

to

coherence must provide.

On

a

machine with physically distributed memory, nonlocal data

may be

repli-

cated either only

in the

processors' caches

or in the

local main memory.

If

coherent

replication

is

provided

in

main memory, additional support

for

keeping caches

coherent

may not be

necessary since only data that

is

already coherent

in the

local

main memory

may

ente ...