An adaptive synchronization method for unpredictable communication patterns in dataparallel programs

Parallel assignments are among the most common constructs in a dataparallel program. The communication patterns implied by a parallel assignment statement may be classified as predictable or unpredictable. Predictable communication patterns can be identified by the compiler and are typically amenable to efficient code generation. Unpredictable communication patterns cannot be detected at compile time and in mast situations are inefficiently implemented using general techniques. The well known inspector-executor method efficiently implements unpredictable communication patterns that repeat themselves, by capturing and saving information the first time, and using it for subsequent repetitions. The primary contribution of this paper is a method that efficiently implements a wide class of unpredictable communication patterns. This class includes patterns that are not necessarily repeated, and so additionally encompasses cases where the inspector-executor method fails. This paper describes the new method and its implementation on the IBM SP1 multicomputer. Experimental results on the performance of this implementation are presented for a variety of synthetic benchmark codes