More Accurate Load Tracking Being Worked On For the ACPI CPPC CPUFreq Driver

The ACPI CPPC (Collaborative Processor Performance Control) Linux CPUFreq driver continues to be improved upon.

CPPC is the ACPI specification around OS management of describing abstract performance scales and a means of being able to request higher/lower performance levels and measuring per-CPU performance. The Linux kernel for a while has offered the ACPI CPPC CPUFreq driver for making use of this standard on supported systems for frequency scaling. So far mostly Arm Linux systems have leveraged ACPI CPPC CPUFreq while last year AMD proposed their own CPPC driver albeit at the moment appears stalled.

We have seen work in recent times by ARM stakeholders on improving CPPC CPUFreq with the likes of boost support while the latest being tackled by the Linaro crew is on frequency invariance. The frequency invariance for CPPC CPUFreq is aiming to deliver more accurate load tracking to make better CPU frequency scaling decisions.

This includes support for ARM systems lacking Activity Monitor Units (AMU) that also provide similar frequency invariance support. The tentative work in this area can be found via this patch series.