PCMT: Prioritizing Coherence Message Types for NoC Protocol-level Deadlock Freedom

The Network-on-Chip (NoC) has emerged as a vital interconnect fabric in multi-core processors. However, the implementation of virtual networks requires multiple message queues at each router’s input port to prevent protocol-level deadlocks, resulting in substantial area and power overheads. This complexity poses challenges in maintaining performance within a constrained area budget. In this paper, we introduce PCMT, a virtual-network-free mechanism that leverages the inherent priority of directory-based coherence messages to resolve protocol-level deadlocks within the NoC. Experimental results show that PCMT outperforms both baseline and state-of-the-art solutions across systems with varying numbers of virtual networks. In a MOESI-hammer protocol system with 6 virtual networks, PCMT achieves comparable performance while reducing input buffer overhead by up to 63% compared to the baseline. In a MOESI directory system with 3 virtual networks, PCMT improves overall execution time by up to 4.0% with the same input buffer resources. Additionally, PCMT demonstrates superior deadlock resolution speed and bandwidth consumption compared to the state-of-the-art work.