LoPC

Abstract

Parallel algorithm designers need computational models that take first order system costs into account, but are also simple enough to use in practice. This paper introduces the LoPC model, which is inspired by the LogP model but accounts for contention for message processing resources in parallel algorithms on a multiprocessor or network of workstations. LoPC takes the L , o and P parameters directly from the LogP model and uses them to predict the cost of contention, C .This paper defines the LoPC model and derives the general form of the model for parallel applications that communicate via active messages. Model modifications for systems that implement coherent shared memory abstractions are also discussed. We carry out the analysis for two important classes of applications that have irregular communication. In the case of parallel applications with homogeneous all-to-any communication, such as sparse matrix computations, the analysis yields a simple rule of thumb and insight into contention costs. In the case of parallel client-server algorithms, the LoPC analysis provides a simple and accurate calculation of the optimal allocation of nodes between clients and servers. The LoPC estimates for these applications are shown to be accurate when compared against event driven simulation and against a sparse matrix computation on the MIT Alewife multiprocessor.