Backdraft: a Lossless Virtual Switch that Prevents the Slow Receiver Problem


Alireza Sanaee, Queen Mary University of London; Farbod Shahinfar, Sharif University of Technology; Gianni Antichi, Queen Mary University of London; Brent E. Stephens, University of Utah


Virtual switches, used for end-host networking, drop packets when the receiving application is not fast enough to consume them. This is called the slow receiver problem, and it is important because packet loss hurts tail communication latency and wastes CPU cycles, resulting in application-level performance degradation. Further, solving this problem is challenging because application throughput is highly variable over short timescales as it depends on workload, memory contention, and OS thread scheduling.

This paper presents Backdraft, a new lossless virtual switch that addresses the slow receiver problem by combining three new components: (1) Dynamic Per-Flow Queuing (DPFQ) to prevent HOL blocking and provide on-demand memory usage; (2) Doorbell queues to reduce CPU overheads; (3) A new overlay network to avoid congestion spreading. We implemented Backdraft on top of BESS and conducted experiments with real applications on a 100 Gbps cluster with both DCTCP and Homa, a state-of-the-art congestion control scheme. We show that an application with Backdraft can achieve up to 20x lower tail latency at the 99th percentile.

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This content is available to:

@inproceedings {278300,
author = {Alireza Sanaee and Farbod Shahinfar and Gianni Antichi and Brent E. Stephens},
title = {Backdraft: a Lossless Virtual Switch that Prevents the Slow Receiver Problem},
booktitle = {19th USENIX Symposium on Networked Systems Design and Implementation (NSDI 22)},
year = {2022},
isbn = {978-1-939133-27-4},
address = {Renton, WA},
pages = {1375--1392},
url = {},
publisher = {USENIX Association},
month = apr,

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