Compass: Congestion Control for Disobedient Traffic

Increasingly stringent service-level objectives demand fast and accurate congestion control (CC) in data center networks. We observe that the feedback loop used by existing data center sender-driven CC schemes is inherently limited as it suffers from an inevitable delay. Consequently, a portion of traffic, which we call disobedient traffic, could finish before the feedback loop, thereby escaping the control of these schemes and exerting a negative impact on their performance. Furthermore, as link speeds continue to climb, the proportion and impact of disobedient traffic are concurrently escalating, exacerbating these issues. In this paper, we propose Compass, a solution implemented entirely on switch data plane to mitigate the impact of disobedient traffic. Compass utilizes sketching techniques to efficiently estimate the sending rate of disobedient traffic, and seamlessly integrates into HPCC and PowerTCP through incorporating the sending rate of disobedient traffic into their high-precision rate control algorithms. Such integration enhances network performance without incurring additional bandwidth overhead or modifications to host-side logic. Additionally, Compass supports incremental brownfield deployment, and all these properties make it highly practical for production deployment. Extensive simulations show that Compass improves both throughput and latency. For instance, Compass reduces tail flow completion times of medium and large flows by up to 35% for PowerTCP and 17% for HPCC.