One More Config is Enough: Saving (DC)TCP for High-Speed Extremely Shallow-Buffered Datacenters
Wei Bai, Shuihai Hu, Kai Chen, Kun Tan, Yongqiang Xiong
Abstract
The link speed in production datacenters is growing fast, from 1 Gbps to 40 Gbps or even 100 Gbps. However, the buffer size of commodity switches increases slowly, e.g., from 4 MB at 1 Gbps to 16 MB at 100 Gbps, thus significantly outpaced by the link speed. In such extremely shallow-buffered networks, today's TCP/ECN solutions, such as DCTCP, suffer from either excessive packet losses or significant throughput degradation. Motivated by this, we introduce BCC, <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sup> a simple yet effective solution that requires only one more ECN configuration (i.e., shared buffer ECN/RED) at commodity switches. BCC operates upon real-time global shared buffer utilization. When available buffer space suffices, BCC delivers both high throughput and low packet loss rate as prior work; When it gets insufficient, BCC automatically triggers the shared buffer ECN to prevent packet loss at the cost of sacrificing a small amount of throughput. BCC is readily deployable with existing commodity switches. We validate BCC's efficacy in a 100G testbed and evaluate its performance using extensive simulations. Our results show that BCC maintains low packet loss rate persistently while only slightly degrading throughput when the buffer becomes insufficient. For example, compared to current practice, BCC achieves up to 94.4% lower 99th percentile flow completion time (FCT) for small flows while only degrading average FCT for large flows by up to 3%.