Skylake X Servers On Linux 4.16 Will Have P-State CPU Frequency Scaling Support

When using Intel Skylake X / Xeon Scalable chips right now under Linux the ACPI CPUFreq driver is responsible for the CPU frequency scaling decisions. But with the upcoming Linux 4.16 kernel cycle, Intel's P-State driver will add support for Skylake X.

Queued changes for Linux 4.16 P-State by means of the power management tree will add Skylake server support when in HWP (Hardware P-States) mode.

Intel Linux developers have said the power/performance results between this new P-State support and CPUFreq are "comparable" -- we'll run some benchmarks on our own once this code is mainlined.

While the results might not be very different, using the P-State driver on Skylake X servers does allow reporting of turbo frequencies rather than just showing the base clock frequencies. Additionally, the P-State driver allows enforcing limits on the turbo frequency range.

There's also some P-State clean-ups and other power management improvements for Linux 4.16 as outlined via this PR. Intel's Rafael Wysocki sent in his pull request already due to traveling to Australia for LCA2018.