Swizzle-Switch Networks for Many-Core Systems

This work revisits the design of crossbar and high-radix interconnects in light of advances in circuit and layout techniques that improve crossbar scalability, obviating the need for deep multi-stage networks. We employ a new building block, the Swizzle-Switch-an energy and area-efficient switching element that can readily scale to radix 64-that has recently been validated via silicon test chips in 45 nm technology. We evaluate the Swizzle-Switch as both the high-radix building block of a Flattened Butterfly and as a single-stage interconnect, the Swizzle-Switch Network. In the process we address the architectural and layout challenges associated with centralized crossbar systems. Compared to a conventional Mesh, the Flattened Butterfly provides a 15% performance improvement with a 2.5× reduction in the standard deviation of on-chip access times. The Swizzle-Switch Network achieves further gains, providing a 21% improvement in performance, a 3× reduction in on-chip access variability, a 33% reduction in interconnect power, and a 25% reduction in total system energy while only increasing chip area by 7%. Finally, this paper details a 3-D integrated version of the Swizzle-Switch Network, showing up to a 30% gain in performance over the 2-D Swizzle-Switch Network for benchmarks sensitive to interconnect latency. One major concern with 3-D designs is thermal dissipation. We show through detailed thermal analysis that with the highly energy-efficient Swizzle-Switch Network design that the thermal budget is well within that of passive cooling solutions.