Transit ring: bubble flow control for eliminating inter-ring communication congestion

• Published in: The Journal of supercomputing Vol. 79; no. 2; pp. 1161 - 1181
• Main Authors: Ouyang, Yiming, Sun, Chenglong, Li, Ruifeng, Wang, Qi, Li, Jianhua
• Format: Journal Article
• Language: English
• Published: New York Springer US 01.02.2023; Springer Nature B.V
• Subjects: Bubbles; Buffers; Communication; Compilers; Computer Science; Design; Flow control; Interpreters; Packets (communication); Processor Architectures; Programming Languages; Toruses; Transit; Congestion; Inter-ring communication; Torus; Bubble flow control; Network-on-chip
• ISSN: 0920-8542; 1573-0484
• DOI: 10.1007/s11227-022-04712-z

Bubble flow control is a flow control mechanism commonly used in torus network. Bubble flow control ensures the orderly flow of packets in the ring by efficiently allocating intra-ring buffer resources and solves the intra-ring deadlock problem. However, inter-ring communication with bubble flow control is subject to strict limitations. When packets are communicated across the rings, starvation may occur, resulting in prolonged blocking within the ring. Inefficient inter-ring communication not only generates Head-of-Line blocking, but also affects the whole intra-ring communication through the backpressure mechanism. We propose a Transit Ring design that establishes an alternate ring link in the torus network by reusing free buffers in the router. By evacuating packets blocking inter-ring communication into the Transit Ring, starvation, as well as Head-of-Line blocking, in the network is eliminated. Compared to state-of-the-art bubble flow control, our proposed design improves saturation throughput by an average of 15.9% in a 4 × 4 torus network and 17.06% in an 8 × 8 torus network.