Bandwidth Efficient All–to–All Broadcast on Switched Clusters

We develop an all-to-all broadcast scheme that achieves maximum bandwidth efficiency for clusters with tree topologies. Using our scheme for clusters with cut-through switches, any tree topology can support allto-all broadcast as efficiently as a single switch connecting all machines when the message size is sufficiently large. Since a tree topology can be embedded in almost any connected network, it follows that efficient all-toall broadcast can be achieved in almost all topologies, regular or irregular. To perform all-to-all broadcast efficiently on clusters with store-and-forward switches, the algorithm must minimize the communication path lengths in addition to maximizing bandwidth efficiency. This turns out to be a harder algorithmic problem. We develop schemes that give solutions to common cases for such systems. The performance of our algorithms is evaluated on Ethernet switched clusters with different topologies. The results confirm our theoretical finding. Furthermore, depending on the topology, our algorithms sometimes out-perform the topology-unaware algorithms used in MPI libraries, including MPICH and LAM/MPI, to a very large degree.