Congestion Quarantine in Lossless Ethernet
Lossless Ethernet uses hop-by-hop backpressure to prevent buffer overflow and has become the mainstream choice for running Remote Direct Memory Access (RDMA) in AI and cloud data centers. Despite preventing congestion-induced drops, lossless networks introduce congestion contagion, which causes head-of-line blocking, congestion spreading, and deadlocks. Congestion control schemes have been introduced to mitigate the drawbacks of lossless Ethernet. However, congestion control mechanisms struggle with bursty traffic, face a dilemma, and can be sidelined by backpressure. In this paper, we propose congestion quarantine (CQ) as a complementary congestion management mechanism for lossless Ethernet. CQ uses a separate queue to quarantine congested flows, preventing congestion contagion, resolving the CC dilemma, and preventing CC from being sidelined. Results show that congestion quarantine can eliminate head-of-line blocking in scenarios with multiple congestion trees. Large-scale simulations demonstrate that CQ reduces the average and 99th percentile FCT slowdown of normal flows by 25–86% and 33.4–90%, respectively, with negligible impact on bursty traffic.