Worm-Bubble Flow Control

Deadlock-free flow control should be designed with minimal cost, particularly for on-chip designs where area and power resources are greatly constrained. While Bubble Flow Control, proposed a decade ago, can avoid deadlock in VCT-switched tori with only one virtual channel (VC), there has been no working solution for wormhole switching that achieves the similar objective. Wormhole switching allows the channel buffer size to be smaller than the packet size, thus is preferred by on-chip networks. However, wormhole packets can span multiple routers, thereby creating additional channel dependences and adding complexities in both deadlock and starvation avoidance. In this paper, we propose Worm-Bubble Flow Control (WBFC), a new flow control scheme that can avoid deadlock in wormhole-switched tori using minimally 1-flit-sized buffers per VC and one VC in total. Moreover, any wormhole-switched topology with embedded rings can use WBFC to avoid deadlock within each ring. Simulation results from synthetic traffic and PARSEC benchmarks show that the proposed approach can achieve significant throughput improvement and also area and energy savings compared to an optimized Dateline routing approach.