Distributed shared memory architecture for JUMP-1 a general-purpose MPP prototype

We describe and evaluate a novel distributed-shared memory (DSM) architecture of JUMP-1, a general-purpose MPP system. For improving performance, JUMP-1 DSM architecture utilizes cooperation of the network, construction of memory-directories and a memory-protocol that unifies memory-consistency, communication and synchronization. Among features of JUMP-1 DSM, we show details of Reduced Hierarchical Bit-map Directory schemes (RHBDs) which utilize hierarchy embedded in the interconnection network for reducing network traffic on shared memory operations. Three variations of the RHBD are implemented on a network called the RDT (Recursive Diagonal Torus) consisting of the hierarchical structure of two-dimensional tori. In RHBDs, the bit map directory is reduced for quick multicasting without accessing the directory in each hierarchy. Most unnecessary packets caused by reduction of the bit map are removed with the pruning cache provided in the router. The results of simulation demonstrate that latency for cache coherent messages is much improved compared with traditional directory schemes.