Toward efficient and robust software speculative parallelization on multiprocessors

Abstract

With speculative parallelization, code sections that cannot be fully analyzed by the compiler are aggressively executed in parallel. Hardware schemes are fast but expensive and require modifications to the processors and memory system. Software schemes require no extra hardware but can be inefficient.This paper proposes a new software-only speculative parallelization scheme. The scheme is developed after a systematic evaluation of the design options available and is shown to be efficient and robust and to outperform previously proposed schemes. The novelty and performance advantage of the scheme stem from the use of carefully tuned data structures, synchronization policies, and scheduling mechanisms. Experimental results show that our scheme has small overheads and, for applications with few or no data dependence violations, realizes on average 71% of the speedup of a manually parallelized version of the code, outperforming two recently proposed software-only speculative parallelization schemes. For applications with many data dependence violations, our performance monitors and switches can effectively curb the performance degradation.