Evaluating the efficiency of openmp tasking for unbalanced computation on diverse cpu architectures

Abstract

In the decade since support for task parallelism was incorporated into OpenMP, its use has remained limited in part due to concerns about its performance and scalability. This paper revisits a study from the early days of OpenMP tasking that used the Unbalanced Tree Search (UTS) benchmark as a stress test to gauge implementation efficiency. The present UTS study includes both Clang/LLVM and vendor OpenMP implementations on four different architectures. We measure parallel efficiency to examine each implementation’s performance in response to varying task granularity. We find that most implementations achieve over 90% efficiency using all available cores for tasks of O(100k) instructions, and the best even manage tasks of O(10k) instructions well.