Contexts: A Mechanism for High Throughput Communication in OpenSHMEM

Abstract

This paper introduces a proposed extension to the OpenSHMEM parallel programming model, called communication contexts. Contexts introduce a new construct that allows a programmer to generate independent streams of communication operations. In hybrid executions where multiple threads execute within an OpenSHMEM process, contexts eliminate interference between threads, and enable the OpenSHMEM library to map operations generated by threads to private communication resource sets. By providing thread isolation, contexts eliminate synchronization overheads and enable each thread to drive a similar set of resources and achieve performance comparable to an OpenSHMEM process. In conventional, single-threaded execution, contexts provide greater control over ordering of operations and can improve communication and computation overlap. A detailed description of the contexts interface and its implementation for the Portals 4 network programming interface is described. The implementation is evaluated using Mandelbrot set and integer sorting (IS) benchmarks. Contexts provide a 25% performance improvement for Mandelbrot by eliminating thread interference and enabling pipelining, and a 35% improvement was achieved for IS by enabling more effective communication/computation overlap.