Download or read book An Evaluation of Directory Protocols for Medium-scale Shared-memory Multiprocessors written by University of Wisconsin--Madison. Computer Sciences Dept and published by . This book was released on 1994 with total page 11 pages. Available in PDF, EPUB and Kindle. Book excerpt: Abstract: "This paper considers alternative directory protocols for providing cache coherence in shared-memory multiprocessors with 32 to 128 processors, where the state requirements of Dir[subscript N] may be considered too large. We consider Dir[subscript i]B, i = 1,2,4, Dir[subscript N], Tristate (also called superset), Coarse Vector, and three new protocols. The new protocols -- Gray-hardware, Gray-software, Home -- are optimizations of Tristate that use gray coding to favor near-neighbor sharing. Our results are the first to compare all these protocols with complete applications (and the first evaluation of Tristate with a non- synthetic workload). Results for three applications -- ocean (one dimensional sharing), appbt (three-dimensional sharing), and barnes (dynamic sharing) -- for 128 processors on the Wisconsin Wind Tunnel show that (a) Dir1B sends 15 to 43 times as many invalidation messages as Dir[subscript N], (b) Gray-software sends 1.0 to 4.7 times as many messages as Dir[subscript N], making it better than Tristate, Gray- Hardware, and Home, and (c) the choice between Dir[subscript i]B, Coarse Vector, and Gray-software depends on whether one wants to optimize for few sharers (Dir[subscript i]B), many sharers (Coarse Vector), or hedge one's bets between both alternatives (Gray-software)."