SIM: Sub-RTT-based Incast Mitigation in Data Center Networks

Recently, many Remote Direct Memory Access (RDMA) congestion control (CC) algorithms have been proposed to ensure the performance of high-speed Data Center Networks (DCNs). However, there is an inherent feedback delay in end-to-end CC, resulting in the inability to exert control over each flow within its first RTT. Upon many-to-one (Incast), the immediate high queue introduces significant latency to the short flows. In this paper, we propose SIM, a Sub-RTT-based Incast mitigation scheme to enhance congestion control. SIM offers two key functionalities: it enables the detection and notification of Incast within Sub-RTT, and it provides an adaptive adjustment algorithm that responds based on the severity of the Incast. Simulation results show that SIM fundamentally reduces the peak queue of Incast and shortens 99% FCT slowdown of short flows by up to 70% and 47% compared to the state-of-the-art congestion control schemes in DCNs, respectively.