FastCredit: Expediting credit-based congestion control in datacenters

Abstract

Receiver-driven transports that leverage hop-by-hop credits have the merits of fast convergence, short queueing, and strong congestion avoidability, making them high-efficiency in managing congestion in current high-speed data centers. However, these transport protocols treat long and latency-sensitive short flows equally, increasing flow completion times and affecting user experiences. Although flow scheduling mechanisms have been studied extensively, they are hard to be deployed into hop-by-hop credit-based transports. The root cause is that most traditional flow scheduling mechanisms mainly work in the long queue containing flows of various sizes, while credit-based proactive transports maintain the extremely short bounded queue.Based on this observation, this paper presents FastCredit, making the first attempt to expedite short-flow scheduling in hop-by-hop credit-based congestion control. In FastCredit, we schedule credit transmission at both receivers and switches to indirectly perform data flow scheduling, and we develop an ECN-based credit rate control mechanism to mitigate the problems caused by credit loss. Compared to the state-of-the-art credit-based transport protocol, FastCredit reduces average flow completion time to 0.71x and greatly improves the short flow transmission latency to 0.45x in realistic workloads. Especially, FastCredit reduces average flow completion time to 0.72x under incast circumstances and 0.56x in many-to-one traffic mode. Moreover, FastCredit still maintains the advantages of the short queue and high throughput and essentially reduces credit loss by employing credit rate control.