Empirical study of latency hiding on a fine-grain parallel processor

Latency associated with memory accesses and process communications are one of the most difficult obstacles in constructing a practical massively parallel system. So far, two approaches to hide latencies have been proposed. They are prefetching and multi-threading. An instruction-level data-driven computer is an ideal test-bed for evaluating these latency hiding methods because prefetching and multi-threading are naturally implemented in an instruction-level data-driven computer as unfolding and concurrent execution of multiple contexts. This paper evaluates latency hiding methods on SIGMA-1, a dataflow supercomputer developed in Electrotechnical Laboratory. As a result of evaluation, these methods are effective to hide static latencies but not effective to hide dynamic latencies. Also, concurrent execution of multiple contexts is more effective than prefetching.