CHAMELEON: Automatic and Adaptive Tuning for DCQCN Parameters in RDMA Networks

Datacenter Quantized Congestion Notification (DCQCN) [12] is the default congestion control algorithm for Mellanox RDMA (Remote Direct Memory Access) NICs [2] in RoCEv2 (RDMA over Converged Ethernet v2) networks, one of the most widely used NICs in leading industry companies [4, 5, 7, 9]. In DCQCN, firstly switches mark packets with ECN (Explicit Congestion Notification) when the queue length exceeds ECN thresholds, then receivers respond to ECN-marked packets with CNPs (Congestion Notification Packets), and finally senders reduce transmission rate when receiving CNPs. DCQCN has 10+ parameters at both NICs and switches, including Alpha Update, Rate Increase & Decrease, Notification Point and ECN thresholds [3], and these parameters have a non-negligible impact on the network performance. Our experiments also verify the network performance of common AI (Artificial Intelligence) training workloads in RoCEv2 networks (e.g., all-to-all collective communication) is greatly influenced by different DCQCN parameter settings ( § 3). Therefore, when deploying applications in practice, the DCQCN parameters need to be carefully tested and tuned to improve the network performance.