Casper: An Asynchronous Progress Model for MPI RMA on Many-Core Architectures

In this paper we present \"Casper,\" a process-based asynchronous progress solution for MPI one-sided communication on multi- and many-core architectures. Casper uses transparent MPI call redirection through PMPI and MPI-3 shared-memory windows to map memory from multiple user processes into the address space of one or more ghost processes, thus allowing for asynchronous progress where needed while allowing native hardware-based communication where available. Unlike traditional thread- and interrupt-based asynchronous progress models, Casper provides the capability to dedicate an arbitrary number of ghost processes for asynchronous progress, thus balancing application requirements with the capabilities of the underlying MPI implementation. We present a detailed design of the proposed architecture including several techniques for maintaining correctness per the MPI-3 standard as well as performance optimizations where possible. We also compare Casper with traditional thread- and interrupt-based asynchronous progress models and demonstrate its performance improvements with a variety of micro benchmarks and a production chemistry application.