Spec-all: aggressive read/write access speculation method for DSM systems

In this paper, we propose a new speculative coherence control method, called spec-all, for DSM systems. Spec-all aims at complete elimination of coherence control overhead, caused by both read and write memory accesses in typical data-sharing patterns. We introduce five speculative coherence transactions in order to realize spec-all. Furthermore, we propose a new speculative coherence control mechanism, named SCCM. SCCM includes two novel predictors that issue the speculative transactions. We have evaluated the effectiveness of spec-all by a simulator. The results show that spec-all achieves 1.59 times better performance than that of the non-speculative method (non-spec), and 1.18 times better one than that of the existing speculative method (spec-read), when the memory access pattern is regular. In this situation, the results reveal that spec-all achieves 77% reduction of memory access latency, compared with non-spec, and 68% reduction, compared with spec-read. Furthermore, we found that spec-all achieves 1.02 times better performance than that of non-spec, and 1.01 times better one than that of spec-read, when we apply the methods to practical programs.