Fast Broadcast and Multicast in Wormhole Multistage Networks with Multidestination Worms

Abstract

: This paper presents a new approach to implement fast broadcast and multicast operations in bidirectional wormhole Multistage Interconnection Networks (MIN) with loopback, as used in IBM SP1/SP2 network. The novelty lies in using multidestination message passing mechanism instead of single destination (unicast) messages. For broadcast/multicast operation, it is shown that a single worm with multiple destinations is sufficient to allow pipelined replication of flits at appropriate intermediate switches and deliver copies to the required destinations. For higher communication start-up (t s ), for an n-processor system, this new approach leads to an asymptotic improvement by a factor of dlog 2 ne compared to the unicast-based messagepassing. Two schemes for broadcast and multicast are presented together with the necessary architectural supports at a switch-level. Storage requirements at a switch to ensure deadlock freedom are also derived. These schemes are evaluated and compared with t..