Practical Packet Deflection in Datacenters

Abstract

Bursts, sudden surges in network utilization, are a significant root cause of packet loss and high latency in datacenters. Packet deflection, re-routing packets that arrive at a local hotspot to neighboring switches, is shown to be a potent countermeasure against bursts. Unfortunately, existing deflection techniques cannot be implemented in today's datacenter switches. This is because, to minimize packet drops and remain effective under extreme load, existing deflection techniques rely on certain hardware primitives (e.g., extracting packets from arbitrary locations in the queue) that datacenter switches do not support. In this paper, we address the implementability hurdles of packet deflection. This paper proposes heuristics for approximating state-of-the-art deflection techniques in programmable switches. We introduce Simple Deflection which deflects excess traffic to randomly selected, non-congested ports and Preemptive Deflection (PD) in which switches identify the packets likely to be selected for deflection and preemptively deflect them before they are enqueued. We implement and evaluate our techniques on a testbed with Intel Tofino switches. Our testbed evaluations show that Simple and Preemptive Deflection improve the 99th percentile response times by 8× and 425×, respectively, compared to a baseline drop-tail queue under 90% load. Using large-scale network simulations, we show that the performance of our algorithms is close to the deflection techniques that they intend to approximate, e.g., PD achieves 4% lower 99th percentile query completion times (QCT) than Vertigo, a recent deflection technique that cannot be implemented in off-the-shelf switches, and 2.5× lower QCT than ECMP under 95% load.