Static and Runtime Scheduling of UnstructuredCommunication 1

With the advent of new routing methods, the distance to which a message is sent is becoming relatively less and less important. Thus assuming no link contention, permutation seems to be an e cient collective communication primitive. All-tomany communication is required for solving a large class of irregular and loosely synchronous problems on distributed memory MIMD machines. In this paper we present several algorithms for decomposing all-to-many personalized communication into a set of disjoint partial permutations. These partial permutations avoid node contention and/or link contention. We discuss several algorithms and study their e ectiveness both from the view of static scheduling as well as runtime scheduling. Experimental results for our algorithms are presented on the iPSC/860. Index Terms Asynchronous communication, link and node contention, loosely synchronous communication, runtime and static scheduling.