The Linux Kernel Continues Being Piped For Intel UMWAIT Support

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.