BMW Tree: Large-scale, High-throughput and Modular PIFO Implementation using Balanced Multi-Way Sorting Tree

Push-In-First-Out (PIFO) queue has been extensively studied as a programmable scheduler. To achieve accurate, large-scale, and high-throughput PIFO implementation, we propose the Balanced Multi-way (BMW) Sorting Tree for real-time packet sorting. The tree is highly modularized, insertion-balanced and pipeline-friendly with autonomous nodes. Based on it, we design two simple and efficient hardware designs. The first one is a register-based (R-BMW) scheme. With a pipeline, it features an impressively high and stable throughput without any frequency reduction theoretically even under more levels. We then propose Ranking Processing Units to drive the BMW-Tree (RPU-BMW) to improve the scalability, where nodes are stored in SRAMs and dynamically loaded into/off from RPUs. As the capacity of BMW-Tree grows exponentially, only a few RPUs are needed for a large scale. The evaluation shows that when deployed on the Xilinx Alveo U200 card, R-BMW improves the throughput by 4.8x compared to the original PIFO implementation, while exhibiting a similar capacity. RPU-BMW is synthesized in GlobalFoundries 28nm process, costing a modest 0.522% (1.043mm(2)) chip area and 0.57MB off-chip memory to support 87k flows at 200Mpps. To our best knowledge, RPU-BMW is the first accurate PIFO implementation supporting over 80k flows at as fast as 200Mpps.