D2FQ: Device-Direct Fair Queueing for NVMe SSDs


Jiwon Woo, Minwoo Ahn, Gyusun Lee, and Jinkyu Jeong, Sungkyunkwan University


With modern high-performance SSDs that can handle parallel I/O requests from multiple tenants, fair sharing of block I/O is an essential requirement for performance isolation. Typical block I/O schedulers take three steps (submit-arbitrate-dispatch) to transfer an I/O request to a device, and the three steps incur high overheads in terms of CPU utilization, scalability and block I/O performance. This motivates us to offload the I/O scheduling function to a device. If so, the three steps can be reduced to one step (submit=dispatch), thereby saving CPU cycles and improving the I/O performance.

To this end, we propose D2FQ, a fair-queueing I/O scheduler that exploits the NVMe weighted round-robin (WRR) arbitration, a device-side I/O scheduling feature. D2FQ abstracts the three classes of command queues in WRR as three queues with different I/O processing speeds. Then, for every I/O submission D2FQ selects and dispatches an I/O request to one of three queues immediately while satisfying fairness. This avoids time-consuming I/O scheduling operations, thereby saving CPU cycles and improving the block I/O performance. The prototype is implemented in the Linux kernel and evaluated with various workloads. With synthetic workloads, D2FQ provides fairness while saving CPU cycles by up to 45% as compared to MQFQ, a state-of-the-art fair queueing I/O scheduler.

FAST '21 Open Access Sponsored by NetApp

Open Access Media

USENIX is committed to Open Access to the research presented at our events. Papers and proceedings are freely available to everyone once the event begins. Any video, audio, and/or slides that are posted after the event are also free and open to everyone. Support USENIX and our commitment to Open Access.

@inproceedings {264838,
author = {Jiwon Woo and Minwoo Ahn and Gyusun Lee and Jinkyu Jeong},
title = {{D2FQ}: {Device-Direct} Fair Queueing for {NVMe} {SSDs}},
booktitle = {19th USENIX Conference on File and Storage Technologies (FAST 21)},
year = {2021},
isbn = {978-1-939133-20-5},
pages = {403--415},
url = {https://www.usenix.org/conference/fast21/presentation/woo},
publisher = {USENIX Association},
month = feb

Presentation Video