Adaptive Tickless Linux Kernel Support Status
Written by Michael Larabel in Linux Kernel on 18 January 2012 at 08:11 AM EST. 1 Comment
Back in 2007 (the Linux 2.6.21 days) the mainline Linux kernel received tickless idle support. With the system idling, the timer tick no longer needlessly goes off with the "NOHZ" feature. Being worked on since last year is now adaptive tickless support, which extends the tickless functionality to non-idle cases.

The original adaptive tickless kernel code was published last August, which received a fair amount of feedback and interest. The main developer behind the "adaptive nohz cpusets" is Frederic Weisbecker. He is still working on this code, which has yet to be mainlined, but has provided a status update as of January.

Weisbecker believes this adaptive tickless support will be of great benefit for high-performance computing, as it can optimize throughput by avoiding the overhead of the timer interrupt, and also for real-time uses with less interrupts being generated so a reduction in latency. Read his August announcement for full details about the work as it's a lengthy e-mail and he does a very nice job explaining this implementation's reasons and other details.

In an email sent out just a few hours ago, there is the Status of Nohz cpusets (adaptive tickless kernel) for January 2012. Weisbecker shares that he is still addressing the issues brought up during the last round of reviews on the patch-set, there's been RCU advancements, a split has occurred between the NOHZ and idle logics, and the work has been rebased atop the Linux 3.3 kernel changes.

A TODO list has been posted to his personal web-site, which at the moment has nine items. There's no estimate at the moment for when he may be publishing the second round of patches for review or when he is targeting mainline integration of this work, which now is out until at least the Linux 3.4 kernel.
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Michael Larabel is the principal author of Phoronix.com and founded the site in 2004 with a focus on enriching the Linux hardware experience. Michael has written more than 10,000 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 OpenBenchmarking.org automated benchmarking software. He can be followed via Twitter or contacted via MichaelLarabel.com.

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