Linux Kernel Gets Patches For New CPU Instructions On Intel Tremont & Later
Written by Michael Larabel in Intel on 23 July 2018 at 11:55 AM EDT. 3 Comments
The open-source upbringing of Intel's Tremont micro-architecture is continuing with some new Linux kernel patches outed today.

Tremont is the successor to Intel's Goldmont / Goldmont Plus micro-architecture utilized in the Geminilake platform with the Atom / Celeron / Pentium Silver processors. Details are still light on these ultra low-voltage Intel Tremont processors, but at least the open-source/Linux support is getting squared away in time for their launch.

Intel's recently updated programming reference guide for their instruction set extensions outlines some new CPU instructions supported by Tremont and later. Those new instructions are now supported in the latest Linux kernel patches out by Intel developers.

These new CPU instructions include movdiri and movdir64b for direct stores and umwait, umonitor, and tpause for user waits. The TPAUSE "Timed Pause" instruction is perhaps most interesting and tells the processor to enter an optimized state of either lightweight power/performance or improved power/performance states. The described benefits are for improving performance of other SMT thread(s) on the system. UMONITOR/UMWAIT can yield power savings during idle.

The new user wait instruction behavior can be toggled via the sysfs /sys/devices/system/cpu/umwait_control/ with these patches for the power/performance optimized "C0.2" state. These Intel Tremont CPU instruction additions for now can be found on the kernel mailing list though should be merged in time for Linux 4.19~5.0 assuming no issues or objections are uncovered.
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