Handling Datatypes in MPI-3 One Sided

With the rise of modern interconnects offering direct remote memory access (RDMA), one sided programming becomes increasingly popular. The MPI-3.0 one sided chapter specifies a programming interface that leverages these features directly. foMPI (fast one-sided MPI, [3]) was introduced as a reference implementation to provide highest performance and minimal overheads. Many applications have to communicate non-consecutive data. In message passing each partner specifies their own MPI datatype (a memory layout), while for one sided communication one process defines both types (for the origin and the target process), which requires different kinds of optimizations for truly one sided implementations. In this work three different strategies are proposed to handle the combination of those MPI datatypes and implement them in foMPI. Those strategies were evaluated with DDTBench, a set of data access pattern micro-applications, which were extended to handle one sided communication. Some cases improved up to a magnitude.