An improvement on the way for the AMD P-State Linux CPU frequency scaling driver and the Linux ACPI Collaborative Processor Performance Control ( [1]CPPC ) code at large is supporting a new "HighestFreq" register to be standardized by a future revision of the ACPI specification.

The CPPC HighestFreq register that is likely to be introduced in the next ACPI spec, ACPI 6.7, is for dealing with systems where the boost ratio cannot be accurately calculated using linear interpolation due to differences between CPU cores on the system where the performance-to-frequency mapping is then not linear.

AMD Linux engineer Mario Limonciello explained in the Linux patch series preparing this CPPC HighestFreq support in advance of it formally being adopted by the ACPI spec:

"On some systems, the boost ratio cannot be accurately calculated using linear interpolation of CPPC performance values because the performance-to-frequency mapping is not linear across all cores.

This series introduces support for the CPPC HighestFreq register. This register is under a proposal with ASWG at the moment and trending for inclusion in ACPI 6.7.

This optionally provides the actual highest frequency eliminating the need for interpolation. When available, this frequency value is used for more accurate CPU capacity calculations and boost ratio determination.

This series brings the existing CPPC definitions up to ACPI 6.6 and then adds support for the ACPI 6.7 proposal."

[2]This patch series is what lays out that initial HighestFreq support for overcoming the limitations of linear interpolation for CPPC.



[1] https://www.phoronix.com/search/CPPC

[2] https://lore.kernel.org/linux-acpi/20260504230141.484743-1-mario.limonciello@amd.com/