Implementing multidestination worms in switch-based parallel systems: architectural alternatives and their impact

Multidestination message passing has been proposed as an attractive mechanism for efficiently implementing multicast and other collective operations on direct networks. However, applying this mechanism to switch-based parallel systems is nontrivial. In this paper, we propose alternative switch architectures with differing buffer organizations to implement multidestination worms on switch-based parallel systems. First, we discuss issues related to such implementation (deadlock-freedom, replication mechanisms, header encoding, and routing). Next, we demonstrate how an existing central-buffer-based switch architecture supporting unicast message passing can be enhanced to accommodate multidestination message passing. Similarly, implementing multidestination worms on an input-buffer-based switch architecture is discussed, and two architectural alternatives are presented that reduce the wiring complexity in a practical switch implementation. The central-buffer-based and input-buffer-based implementations are evaluated against each other, as well as against the corresponding software-based schemes. Simulation experiments under a range of traffic (multiple multicast, bimodal, varying degree of multicast, and message length) and system size are used for evaluation. The study demonstrates the superiority of the central-buffer-based switch architecture. It also indicates that under bimodal traffic the central-buffer-based hardware multicast implementation affects background unicast traffic less adversely compared to a software-based multicast implementation. These results show that multidestination message passing can be applied easily and effectively to switch-based parallel systems to deliver good multicast and collective communication performance.