Analyzing One-Sided Communication Using Memory Access Diagrams

n recent years, one-sided communication has emerged as an alternative to message-based communication to improve the scalability of distributed programs. Decoupling communication and synchronization in such programs allows for more asynchronous execution of processes, but introduces new challenges to ensure program correctness and efficiency. The concept of memory access diagrams presented in this paper opens up a new analysis perspective to the programmer. Our approach visualizes the interaction of synchronous, asynchronous, and remote memory accesses. We present an interactive tool that can be used to perform a postmortem analysis of a distributed program execution. The tool supports hybrid parallel programs, shared MPI windows, and GASPI communication operations. In two application studies taken from the European aerospace industry we illustrate the usefulness of memory access diagrams for visualizing and understanding the logical causes of programming errors, performance flaws, and to find optimization opportunities