Mechanisms for cooperative shared memory
Wood, DA; Chandra, S; Falsafi, B; Hill, MD; Larus, JR; Lebeck, AR; Lewis, JC; Mukherjee, SS; Palacharla, S; Reinhardt, SK
Published in: Conference Proceedings Annual Symposium on Computer Architecture
This paper explores the complexity of implementing directory protocols by examining their mechanisms - primitive operations on directories, caches, and network interfaces. We compare the following protocols: Dir1B, Dir4B, Dir4NB, DirnNB, Dir1SW and an improved version of Dir1SW (Dir1SW+). The comparison shows that the mechanisms and mechanism sequencing of Dir1SW and Dir1SW+ are simpler than those for other protocols. We also compare protocol performance by running eight benchmarks on 32 processor systems. Simulations show that Dir1SW+'s performance is comparable to more complex directory protocols. The significant disparity in hardware complexity and the small difference in performance argue that Dir1SW+ may be a more effective use of resources. The small performance difference is attributable to two factors: the low degree of sharing in the benchmarks and Check-In/Check-Out (CICO) directives.
