Performance Evaluation of Different Implementation Schemes of an Iterative Flow Solver on Modern Vector Machines

Abstract

Modern supercomputers consist of multi-core processors, and these processors have recently employed vector instructions, or so-called SIMD instructions, to improve performances. Numerical simulations need to be vectorized in order to achieve higher performance on these processors. Various legacy numerical simulation codes that have been utilized for a long time often contain two versions of source codes: a non-vectorized version and a vectorized version that is optimized for old vector supercomputers. It is important to clarify which version is better for modern supercomputers in order to achieve higher performance. In this paper, we evaluate the performances of a legacy fluid dynamics simulation code called FASTEST on modern supercomputers in order to provide a guidepost for migrating such codes to modern supercomputers. The solver has a nonvectorized version and a vectorized version, and the latter uses the hyperplane ordering method for vectorization. For the evaluation, we also implement the red-black ordering method, which is another way to vectorize the solver. Then, we examine the performance on NEC SX-ACE, SXAurora TSUBASA, Intel Xeon Gold, and Xeon Phi. The results show that the shortest execution times are with the red-black ordering method on SX-ACE and SX-Aurora TSUBASA, and with the non-vectorized version on Xeon Gold and Xeon Phi. Therefore, achieving a higher performance on multiple modern supercomputers potentially requires maintenance of multiple code versions. We also show that the red-black ordering method is more promising to achieve high performance on modern supercomputers.