Open Source Summit Europe 2022

AMD CPU platforms used ACPI based CPU frequency driver to manage CPU frequencies with switching only in 3 P-states for a long time. ACPI CPUFreq is very great driver to support frequency control on traditional AMD processors. However, for recent Zen2 and later CPUs, this approach is not very power efficient anymore and conflicts with AMD hardware dynamic power management unit. So, we introduce AMD P-State kernel CPUFreq driver early of this year that is using ACPI CPPC based fine grain frequency control instead of legacy only 3 ACPI P-States, and it is merged into kernel 5.17. Then we continue adding the CPUPower and AMD P-State tracer support in kernel 5.18. And we are in progress to add the related AMD P-State unit tests into kselftest framework. This is the initial work that we start to support new fine grain frequency control in CPUFreq subsystem, so we still have a long way to continue optimizing the new driver on all AMD recent CPU and APU platforms and adding more feature support including EPP (Energy-Performance Preference), Preferred Core, etc. in future. In this session, Ray will give the introduction of new fine grain frequency control mechanism and explain the details that cover the design, implementation, usage, existing issues, and future work for all AMD CPU users.