OFC: An Original Congestion-Based Fine-grained Priority Flow Control

With the proliferation of online data intensive applications and virtualized services, the growing complexity of traffic patterns in data centers increases the likelihood of congestion, especially in incast scenarios and with a combination of short and large flows. To ensure lossless transmission, RDMA over Converged Ethernet networks rely on Priority-based Flow Control (PFC) to prevent packet loss due to buffer overflow. However, it is widely acknowledged that PFC gives rise to several issues, such as Congestion Spreading, Head-of-Line Blocking, and Deadlock, which are increasingly prominent in modern highly congested data centers. In this paper, we analyze the primary causes of congestion spreading and head-of-line blocking issues associated with PFC and propose Original congestion-based fine-grained priority Flow Control (OFC) as a solution. The performance of OFC is assessed using the programmable switch Tofino and simulations carried out with a packet-level simulator across various scenarios, encompassing incast, realistic, deadlock, and in-depth scenarios. The validation of the simulation results through testbed evaluation confirmed that OFC effectively reduces flow completion time, buffer occupancy, and deadlock occurrence by up to 60.28%, 51.47%, and 48.7%, respectively.