Addressing Endpoint-Induced Congestion for Accelerator Scale-Out in a Medium-Scale Domain

The rapid advancement of network link bandwidth in modern data centers, coupled with the relatively slower processing capabilities of host systems that include accelerators, has given rise to a new challenge: endpoint congestion. This paper presents a reactive scheme built upon a standard reliability protocol to mitigate the impact of endpoint congestion in a medium-scale domain of endpoints-one that is reachable within a few switch hops. This is arguably the sweet-spot for an accelerator scale-out domain. The proposed policy, which overloads duplicate-ACK as a reactive congestion signal, enables controlled pacing of packets from the initiator to match with target processing bandwidth, thereby avoiding packet loss due to endpoint congestion. Our results demonstrate that, for unicast and incast streaming PUT (RDMA write) flows, the proposed scheme effectively mitigates packet drops and achieves minimal, or in most cases zero, packet retransmissions when there is a drop in the endpoint processing speed. Traditional approaches fail to achieve this behavior even with high target queue capacity. Thus, our scheme also has the potential benefit of reducing the buffering requirements at the endpoint and consequently, the cost. To the best of our knowledge, our scheme is the first to explicitly consider and mitigate packet loss due to endpoint congestion, offering an effective approach to address this emerging challenge.