High Radix Interconnection Networks
Google Tech Talks
October 5, 2006
William J. Dally
Bill Dally is the Willard R. and Inez Kerr Bell Professor of Engineering and the Chairman of the Department of Computer Science at Stanford University. Bill and his group have developed system architecture, network architecture, signaling, routing, and synchronization technology that can be found in most large parallel computers today.
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.