Dynamic Thread Pinning for Phase-Based OpenMP Programs

Abstract. Thread affinity has appeared as an important technique to improve the overall program performance and for better performance stability. However, if we consider a program with multiple phases, it is unlikely that a single thread affinity produces the best program performance for all these phases. If we consider the case of OpenMP, applications may have multiple parallel regions, each with a dis-tinct inter-thread data sharing pattern. In this paper, we propose an approach that allows to change thread affinity dynamically (thread migrations) between parallel regions at runtime to account for these distinct inter-thread data sharing patterns. We demonstrate that as far as cache sharing is concerned for SPEC OMP01, not all the tested OpenMP applications exhibit a distinct phase behavior. However, we show that while fixing thread affinity for the whole execution may improve performance by up to 30%, allowing dynamic thread pinning may improve per-formance by up to 40%. Furthermore, we provide an analysis about the required conditions to improve the effectiveness of the approach