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This paper describes the design and implementation of mechanisms for latency tolerance in the remote memory access communication on clusters equipped with high-performance networks such as Myrinet. It discusses strategies that bridge the gap between user-level requirements and network-specific communication interfaces while attempting to increase opportunities for latency hiding. Mechanisms for overlapping communication with computation and coalescing small messages (trading latency for bandwidth) are explored. The effectiveness of these techniques is evaluated using microbenchmarks and application kernels including the NAS parallel benchmark suite. The microbenchmark results showed a better degree of overlap for nonblocking operations in ARMCI as compared to MPI. Application results showed up 30% to 45% improvement over MPI on using nonblocking operations. The aggregation of small messages yielded performance improvement of up to 78% over non-aggregated communication.
Date of Conference: 1-4 Dec. 2003