High Radix Interconnection Networks
ABSTRACT: High-radix interconnection networks offer significantly better cost/performance and lower latency than conventional (low-radix) topologies. Increasing radix is motivated by the exponential increase in router pin bandwidth over time. Increasing the radix or degree of a router node is a more efficient way to exploit this increasing bandwidth than making channels wider. A high-radix poses several challenges in router design because the internal structures of conventional routers (e.g., the allocators) scale quadratically with radix. A hierarchical switch organization with internal buffering yields a scalable design with near-optimal performance. A high-radix "flattened butterfly" topology, enabled by recent developments in global adaptive routing, offers twice the performance as a comparable-cost Clos network on balanced traffic. Many of these developments have been incorporated in the YARC router and interconnection network for the Cray Black Widow Supercomputer.