C3: A Parallel Model for Coarse-Grained Machines

In this paper, we propose a model for parallel computation, tile C3-modcl. The C3 _ model evaluates, for a given parallel algorithm and target architecture, the complexity of computation, the pattern of communication, and the potential congestion arising during communication. A metric for estimating the effect of link and processor congestion on the performance of a communication operation is developed. This metric allows the evaluation of arbiLrary communication operations without the user having to specify fine scheduling details. We describe how the C3-model can serve a'i a platform for the development of coarsegrained algorithms sensitive to the parameters of a parallel machine. The initial validation of the C3-model is discussed for the Inlel Touchstone Delta. We compare predicted and actual performance of different solutions for communication operations and of various divide-andconquer approaches for contour ranking on images.