Roundabout: Solving PFC Deadlocks With Distributed Detection and Buffer Collaboration

RDMA over Converged Ethernet (RoCEv2) employs Priority-based Flow Control (PFC) for a lossless fabric to maintain high performance. However, PFC can cause Deadlocks, which pauses traffic and potentially leads to severe exceptions for applications. Existing solutions solve deadlocks at a considerable cost, resulting in degradation of end-to-end network performance.We present Roundabout, a data plane scheme designed to detect and resolve deadlocks with minimal side effects. We first analyze how switches in different states contribute to deadlocks. Based on the analysis, we design an election-based distributed detection scheme that efficiently and robustly identifies deadlocks. By exploiting buffer configuration redundancy, we develop an innetwork collaborative packet scheduling scheme that forwards deadlocked packets to their destinations in a lossless manner, facilitating natural deadlock resolution. Additionally, we implement a barrier mechanism to ensure in-order packet delivery to the receiver. Both analysis and experiments demonstrate that Roundabout effectively detects and resolves deadlocks while minimizing side effects to the network, making it an ideal enhancement for PFC switches.