Relaxed Synchronization Message Passing

Traditional message-passing (TMP) is characterized by multiple, individual, point-to-point, typed messages, in- ducing unintended temporal synchronization. Asyn- chronous communication can hide some of the overhead and latency from an application, but doing so changes neither the behavior of nor the demands placed upon the communication substrate; messages of the same size are sent at approximately the same times whether syn- chronous or asynchronous communication is used. Relaxed synchronization message passing (RSMP) ad- dresses these issues by eliminating the need for mes- sage types, by amortizing communication overhead costs over larger data transfers, by easing synchronization con- straints across multiple processes, and by minimizing or completely eliminating synchronization costs. Implemen- tation of RSMP is more straightforward, with a less com- plex programming model, yet still provides a system about which application designers, their clients, and theoreti- cians may reason easily. The performance of RSMP on a suite of applications displaying a spectrum communication behaviors shows speedups of 1.136 to 1.339 over an optimized tradi- tional message-passing implementation. Counterintu- itively though, best performance is not always achieved when multiple messages are coalesced into single, large transfers. Larger message sizes favor sending messages individually as soon as data are available. After defining the RSMP model, this paper describes implementation techniques, and provides both platform- independent and platform-dependent evidence of its ad- vantages.