The Two New I/O Controllers and BFQ

Tuesday, February 25, 2020 - 9:30 am10:00 am

Paolo Valente, Department of Physics, Computer Science and Mathematics - University of Modena and Reggio Emilia - Italy

Abstract: 

Two new I/O controllers landed in Linux: io.latency and io.cost. They are aimed at controlling latency and bandwidth, respectively. Yet both quantities are guaranteed by the BFQ I/O scheduler as well. So, when should we use BFQ and when these controllers? Unfortunately, there is no comprehensive documentation answering this question.

To address this issue, in this presentation we compare these new controllers with BFQ, in terms of both interface and performance. Unfortunately, the most important result shown in this presentation is that both controllers apparently exhibit a bad performance, on all systems used in our tests. The root problem seems that they fail to control I/O with common workloads.

Paolo Valente, Department of Physics, Computer Science and Mathematics - University of Modena and Reggio Emilia - Italy

Paolo Valente is an Assistant Professor of Computer Science at the University of Modena and Reggio Emilia, Italy, and a collaborator of the Linaro engineering organization. Paolo's main activities focus on scheduling algorithms for storage devices, transmission links and CPUs. In this respect, Paolo is the author of the last version of the BFQ I/O scheduler. BFQ entered the Linux kernel from 4.12, providing unprecedented low-latency and fairness guarantees. As for transmission links, Paolo is one of the authors of the QFQ packet scheduler, which has been in the Linux kernel until 3.7, after that it has been replaced by QFQ+, a faster variant defined and implemented by Paolo himself. Finally, Paolo has also defined and implemented other algorithms, part of which are now in FreeBSD, and has provided new theoretic results on multiprocessor scheduling.

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BibTeX
@conference {246556,
author = {Paolo Valente},
title = {The Two New I/O Controllers and {BFQ}},
year = {2020},
address = {Santa Clara, CA},
publisher = {{USENIX} Association},
month = feb,
}

Presentation Video