Advanced collective communication in aspen

Abstract

Aspen is a programming language that relies on high-level messaging to support communication among different program tasks executing in parallel. Unlike MPI, the computational logic of Aspen tasks is specified and developed independently of the global communication structure of the program. A root module specifies the communication structure of the program. The semantics and generality of these specifications enable novel forms of collective communication, including asynchronous and concurrent collective operations and reduction type operations with subsets of the participants being receivers of the reduced data, and with receivers that do not provide data to the reduction. This paper describes efficient implementations of these and other collective communication operations in Aspen. We demonstrate the ease-of-use of these features using several code examples and quantify their performance impact through both microbenchmarks and a quantum chemistry code used in rubber chemistry. Aspen's performance is competitive with, or slightly better than, the performance of MPI implementations for both the chemistry application and the microbenchmarks.