Parallel Computer Architecture

8.2 Overview of Directory-Based Approaches 559

cache coherence differ substantially in the mechanisms they provide for three impor-

tant functions that may need to be performed when an access fault occurs:

1.

Finding out enough information about the state of the location (cache block)

in other caches to determine what action to take

2.

Locating those other copies, if needed (e.g., to invalidate them)

3.

Communicating with the other copies (e.g., obtaining data from them or

invalidating or updating them)

In snooping protocols, all three functions are performed by the broadcast and

snooping mechanism. The processor puts a "search" request on th ...