Building a High-Performance Collective Communication Library

We report on a project to develop a unified approach for building a library of collective communication operations that performs well on a cross-section of problems encountered in real applications. The target architecture is a two-dimensional mesh with worm-hole routing, but the techniques are more general. The approach differs from traditional library implementations in that we address the need for implementations that perform well for various sized vectors and grid dimensions, including non-power-of-two grids. We show how a general approach to hybrid algorithms yields performance across the entire range of vector lengths. Moreover, many scalable implementations of application libraries require collective communication within groups of nodes. Our approach yields the same kind of performance for group collective communication. Results from the Intel Paragon system are included

Broadcasting in wraparound meshes with parallel monodirectional links

International audienceIn this paper we give an algorithm to broadcast a message in a wraparound mesh distributed-memory parallel architecture with parallel monodirectional links. This algorithm uses a general strategy based on the diffusion of the message in edge-disjoint spanning trees. We first present in this setting the results of Saad and Schultz and the improvements obtained by Simmen. We then give an asymptotically optimal broadcasting algorithm improving the preceding results. It uses in the wraparound mesh the constructions of two edge-disjoint spanning trees rooted at a given node and of minimum depth