Multiprocessors and Thread-Level Parallelism Distributed Shared Memory and Directory-Based Coherence “ A directory protocol also can be used to reduce the bandwidth demands in a centralized shared-memory machine, as the Sun T1 design does.” Hennessy and Patterson

Distributed Shared Memory

Cache block states: Shared: block cached, value up to date Uncached: No processor has a copy Modified: Has an owner, memory out of date Directory-Based Coherence: The Basics

Cache block states:

Shared: block cached, value up to date

Uncached: No processor has a copy

Modified: Has an owner, memory out of date

Messages among processors and directories

Example of a Directory Protocol

Example of a Directory Protocol

Thank you! Author: Prof. Sergio Takeo, Marcelo Arbore. Bibliography: Patterson, D. A.; Hennessy, J. L. Computer Architecture: A quantitative Approach, 4 th Ed. Morgan Kaufmann Publishers. “ A directory protocol also can be used to reduce the bandwidth demands in a centralized shared-memory machine, as the Sun T1 design does.” Hennessy and Patterson