Annulus: A Dual Congestion Control Loop for Datacenter and WAN Traffic Aggregates
Annulus: A Dual Congestion Control Loop for Datacenter and WAN Traffic Aggregates
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DOI：
10.1145/3387514.3405899
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发表时间：
2020-07
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通讯作者：
Ahmed Saeed;Varun Gupta;Prateesh Goyal;M. Sharif;Rong Pan;M. Ammar;E. Zegura;K. Jang;Mohammad Alizadeh;A. Kabbani;Amin Vahdat
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作者：
Ahmed Saeed;Varun Gupta;Prateesh Goyal;M. Sharif;Rong Pan;M. Ammar;E. Zegura;K. Jang;Mohammad Alizadeh;A. Kabbani;Amin Vahdat
云服务部署在通过高带宽广域网 (WAN) 连接的数据中心中。我们发现 WAN 流量会对数据中心流量的性能产生负面影响，尽管带宽需求较小，但尾部延迟会增加 2.5 倍。此行为是由于 WAN 流量的往返时间 (RTT) 较长以及数据中心交换机中的缓冲有限造成的。长 WAN RTT 迫使数据中心流量承担应对拥塞的全部负担。此外，数据中心流量变化的时间尺度比 WAN RTT 更快，这使得 WAN 拥塞控制难以准确估计可用带宽。我们提出了 Annulus，一种拥塞控制方案，它依靠两个控制循环来应对这些挑战。一个控制循环利用现有的拥塞控制算法来解决只有一种类型的流量（即 WAN 或数据中心）的瓶颈。另一个环路使用来自瓶颈的直接反馈来处理流量源附近的 WAN 和数据中心流量之间共享的瓶颈。我们在测试台和模拟中实现了 Annulus。与使用 BBR 进行 WAN 拥塞控制和使用 DCTCP 或 DCQCN 进行数据中心拥塞控制的基线相比，Annulus 将瓶颈利用率提高了 10%，并将数据中心流完成时间缩短了 1.3-3.5 倍。
Cloud services are deployed in datacenters connected though high-bandwidth Wide Area Networks (WANs). We find that WAN traffic negatively impacts the performance of datacenter traffic, increasing tail latency by 2.5x, despite its small bandwidth demand. This behavior is caused by the long round-trip time (RTT) for WAN traffic, combined with limited buffering in datacenter switches. The long WAN RTT forces datacenter traffic to take the full burden of reacting to congestion. Furthermore, datacenter traffic changes on a faster time-scale than the WAN RTT, making it difficult for WAN congestion control to estimate available bandwidth accurately. We present Annulus, a congestion control scheme that relies on two control loops to address these challenges. One control loop leverages existing congestion control algorithms for bottlenecks where there is only one type of traffic (i.e., WAN or datacenter). The other loop handles bottlenecks shared between WAN and datacenter traffic near the traffic source, using direct feedback from the bottleneck. We implement Annulus on a testbed and in simulation. Compared to baselines using BBR for WAN congestion control and DCTCP or DCQCN for datacenter congestion control, Annulus increases bottleneck utilization by 10% and lowers datacenter flow completion time by 1.3-3.5x.