MSCS: Multi-hop Segmented Circuit Switching

Abstract

NoCs (networks-on-chip) are commonly proposed as scalable on-chip interconnects for current and future CMPs (chip multi-processors) and many-core systems. While scalable, the lack of global control can create routing inefficiencies detrimental to the overall network latency. Recently, NoCs have been proposed that allow flits to traverse multiple network switches in a single cycle. This requires a more global view of control to allow routers along the path of a packet to configure their switches collectively. In this paper, we propose a reservation based circuit-switching design, MSCS, which provides simplified global control and multi-hop traversal while reducing latency. MSCS performs network control once per network dimension for the lifetime of a packet, while the leading methods require multiple arbitration steps depending on contention in the network. Furthermore, MSCS can perform control for a packet prior to the availability of resources through reservations, while previous schemes only perform control on-demand. Overall, MSCS can reduce the buffer size by 50% over the leading multi-hop scheme while maintaining a nominal latency improvement (1.4%). With the same buffer resources per port, MSCS achieves a 12.7% latency improvement.