Reservation Cut-through Switching Allocation for High-Radix Clos Network on Chip

Clos Network on Chip (CNOC) is a promising Network on Chip (NOC) topology because of its low hop counts and good load-balancing characteristics. The throughput of a CNOC depends on the specific router design, which includes at least two major components: buffering structure and switching allocation (SA). In this paper, we propose three cut-through SA schemes for Virtual Output Queue (VOQ)-based NOC routers. The proposed cut-through SA schemes have two major advantages over the flit-mode SA scheme: (1) eliminate the Tail of Line (TOL) blocking suffered by the VOQ structure, and (2) improve the quality of matching obtained in each SA without increasing the iterations. Besides that, the proposed reservation cutthrough SA scheme can cure the potential starvation problem involved in cut-through switching. The performances of the proposed cut-through SA schemes are evaluated based on a 64-node CNOC as well as a 36-node 2D Mesh network. Simulation results show that the cut-through SA schemes significantly improve the performance of CNOC and 2D Mesh network in terms of transmission latency and throughput, even in those extreme scenarios when there are long packets that cannot be switched using cut-through or the input buffer size is very small. Compared to the baseline router, the router with cut-through SA can still achieve a frequency of 1GHz using 65nm technology with only 7.5% increase in area and 11% increase in power consumption.