BRT: Buffer Management for RDMA/TCP Mix-Flows in Datacenter Networks

The coexistence of RDMA and TCP is prevalent in the datacenter. Despite the sound isolation at the end hosts, they share the same switches in the network. Their different networking behaviors (e.g., in hardware demand and transport protocols) lead to huge differentiated buffer demand for switches. However, existing buffer management schemes ignore these dissimilarities and simply treat such RDMA/TCP mix-flows as the typical multi-class traffic, resulting in inferior isolation and degrading networking performances. This paper presents BRT, a first systematic solution for the buffer management of RDMA/TCP mix-flows in the DCN. BRT’s key insight is to allocate buffer with the awareness of traffic’s networking characteristics while minimally impacting the other’s performance. Guided by this insight, it first employs a traffic characteristics-based window to detect whether queues are in the state of persistent long queues. Then, it adjusts the total allocated buffer for each traffic type based on the number of persistent long queues and the normalized dequeue rates to reduce the buffer occupancy of meaningless queuing. Last, it calculates the buffer threshold for RDMA/TCP queues separately and uses a simple yet effective approach to prioritize the absorption of small flows. Our large-scale packet-level evaluations show that BRT can effectively optimize the networking performances for RDMA/TCP mix-flows. For example, compared to current practice, BRT achieves up to 53.5%, 46.7%, and 48.5% lower average FCT for incast flows, RDMA small flows, and TCP small flows, respectively, without sacrificing the overall throughput.