The Linux Kernel Continues Being Piped For Intel UMWAIT Support
Written by Michael Larabel in Intel on 29 May 2019 at 12:10 AM EDT. 2 Comments
INTEL --
Nearly a year ago we reported on the initial work done by Intel's Linux team on adding new CPU instructions for Tremont CPU cores, in particular the new UMWAIT instructions for enhancing power-savings during idle periods. That code continues to be revised for the UMWAIT kernel support but it has yet to be mainlined.

Last week the third public revision to the UMWAIT kernel enablement was sent out. UMWAIT allows for monitoring a range of addresses while in a lightweight power/performance state or an enhanced mode that can still help with conserving power but less so in order to offer lower latencies. UMWAIT is intended to be used as an alternative to kernel spinloops when needing to wait/sleep for short periods of time. Using UMWAIT can conserve power while also helping the performance of Hyper Threading sibling cores.

The GCC 9 compiler is already shipping with UMWAIT instruction support while it's the kernel support that is still being settled for these user wait instructions. The latest patches for those interested can be found here. Hopefully this UMWAIT support (and the related UMONITOR / TPAUSE support) will be ready to go with the Linux 5.3 kernel cycle.

The first Intel CPUs with these new instructions is Tremont as the 10nm Atom successor to Goldmont Plus that should be out later this calendar year.
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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 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 OpenBenchmarking.org automated benchmarking software. He can be followed via Twitter or contacted via MichaelLarabel.com.

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