Fast Congestion Control in RDMA-based Datacenter Networks
Jaichen Xue, Muhammad Usama Chaudhry, Balajee Vamanan, T. N. Vijaykumar, Mithuna S. Thottethodi · 2018
Many modern, interactive datacenter applications have tight latency requirements due to stringent service-level agreements (e.g., under 200 ms for Web Search).TCP-based datacenter networks significantly lengthen the application latency.Remote Direct Memory Access (RDMA) substantially reduces latencies compared to TCP by bypassing the operating system via hardware support at the network interface (e.g., RDMA over InfiniBand and RDMA over Converged Ethernet (RoCE) can cut TCP's latency by 10x [8]).As such, RDMA may soon replace TCP in datacenters.Employing RDMA in datacenters, however, poses a challenge.RDMA provides hop-by-hop flow control and ratebased end-to-end congestion control [4].However, RDMA's congestion control is suboptimal for the well-known datacenter congestion problem, called incast, where multiple flows collide at a switch causing queuing delays and long latency tails [1] despite good network design [7].Though such congestion affects only a small fraction of the flows (e.g., 0.1%), datacenter applications' unique characteristics imply that the average latency is worsened.For example, because Web Search aggregates replies from thousands of