SKQ: Event Scheduling for Optimizing Tail Latency in a Traditional OS Kernel


Siyao Zhao, Haoyu Gu, and Ali José Mashtizadeh, University of Waterloo


This paper presents Schedulable Kqueue (SKQ), a new design to FreeBSD Kqueue that improves application tail latency and low-latency throughput. SKQ introduces a new scalable architecture and event scheduling. We provide multiple scheduling policies that improve cache locality and reduce workload imbalance. SKQ also enables applications to prioritize processing latency-sensitive requests over regular requests.

In the RocksDB benchmark, SKQ reduces tail latency by up to 1022× and extends the low-latency throughput by 27.4×. SKQ also closes the gap between traditional OS kernel networking and a state-of-the-art kernel-bypass networking system by 83.7% for an imbalanced workload.

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@inproceedings {273931,
author = {Siyao Zhao and Haoyu Gu and Ali Jos{\'e} Mashtizadeh},
title = {{SKQ}: Event Scheduling for Optimizing Tail Latency in a Traditional {OS} Kernel},
booktitle = {2021 USENIX Annual Technical Conference (USENIX ATC 21)},
year = {2021},
isbn = {978-1-939133-23-6},
pages = {759--772},
url = {},
publisher = {USENIX Association},
month = jul,

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