Polymorphic data layout for SX-aurora tsubasa vector engines

This paper presents an extension of Kokkos for modern vector processors, such as Vector Engines of SX-Aurora TSUBASA (VEs). Kokkos is a C++ library that provides polymorphic memory access patterns, and widely used for keeping high performance portability of applications. Although Kokkos does not officially support VEs as of July 2020, VEs can execute standard C++ programs, and the original Kokkos can indeed be compiled for VEs. However, the memory access pattern provided by Kokkos for standard processors is not necessarily suited for VEs. For example, it is known that memory access conflicts could drastically degrade the sustained memory bandwidth on VEs, even though, for memory access conflicts, standard processors assumed in Kokkos, i.e., x86 processors, are less performance-sensitive than VEs. Therefore, we propose an extended Kokkos implementation for VEs, which can provide memory access patterns suited for VEs. Specifically, we mainly focus on avoiding memory access conflicts on VEs. This paper introduces a mechanism to automatically avoid memory access conflicts, and explains its implementation. We evaluate our proposal using some benchmark codes, and the results demonstrate that our proposal can successfully exploit the high memory bandwidth of VEs.