The New Restartable Sequences System Call Is Living Up To Its Performance Claims

Written by Michael Larabel in Linux Kernel on 27 October 2018 at 07:07 AM EDT. Add A Comment
Introduced in the Linux 4.18 kernel was the Restartable Sequences "rseq" system call intended to yield faster user-space operations on per-CPU data. As covered during a presentation at this week's Open-Source Summit Europe, that system call is indeed providing performance wins while it's not widely utilized yet.

The restartable sequences system call allows for faster performance in per-CPU data updates from user-space for items like incrementing per-CPU counters, modifying data protected by per-CPU spinlocks, reading/writing per-CPU ring buffers, and similar operations while the kernel guarantees atomic behavior. The RSEQ system call was merged for Linux 4.18 while in the newly-released Linux 4.19 kernel the syscall is supported on ARM64 and other architectures.

There still is ongoing work for improving Restartable Sequences especially with utilizing this syscall from different key components in the Linux user-space, but it's looking like the performance benefits are worthwhile. Mathieu Desnoyers of EfficiOS presented at this week's Open-Source Summit Europe in Edinburgh where he covered this interesting kernel work. The benchmark results are what excited us the most:

Those wishing to learn more about the ongoing RSEQ syscall and weren't able to make it to Edinburgh for the event, Desnoyers' slide deck can be viewed here (PDF). There is also another presentation by Mathieu back from Linux Plumbers 2016 with more background information on this system call if you are interested in more reading this weekend.
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Michael Larabel is the principal author of and founded the site in 2004 with a focus on enriching the Linux hardware experience. Michael has written more than 20,000 articles covering the state of Linux hardware support, Linux performance, graphics drivers, and other topics. Michael is also the lead developer of the Phoronix Test Suite, Phoromatic, and automated benchmarking software. He can be followed via Twitter, LinkedIn, or contacted via

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