AMD Preferred Core Patches Updated For Linux

On the AMD CPU side of the house, one of the patch series we are looking forward to seeing upstreamed in the Linux kernel is the AMD Preferred Core functionality that was initially sent out this summer. This AMD Preferred Core handling is built onto the AMD P-State driver and has been undergoing a few rounds of iteration with the latest "v5" patches having been posted this week.

AMD CPUs since the Ryzen 3000 series (Zen 2) have had the notion of "preferred cores" that via ACPI CPPC are communicated to the OS and could be shown under Windows with the likes of AMD Ryzen Master. With the work-in-progress AMD P-State driver patches, this preferred cores handling is finally coming to Linux. The AMD Linux patches sum up the Preferred Core functionality as:

"The core frequency is subjected to the process variation in semiconductors. Not all cores are able to reach the maximum frequency respecting the infrastructure limits. Consequently, AMD has redefined the concept of maximum frequency of a part. This means that a fraction of cores can reach maximum frequency. To find the best process scheduling policy for a given scenario, OS needs to know the core ordering informed by the platform through highest performance capability register of the CPPC interface.

Earlier implementations of amd-pstate preferred core only support a static core ranking and targeted performance. Now it has the ability to dynamically change the preferred core based on the workload and platform conditions and accounting for thermals and aging.

Amd-pstate driver utilizes the functions and data structures provided by the ITMT architecture to enable the scheduler to favor scheduling on cores which can be get a higher frequency with lower voltage. We call it amd-pstate preferred core."

Available for testing now are the v5 patches for this preferred core integration. The updated patches have been re-based against the Linux-Next state, the sysfs attribute for the CPPC highest performance level has been updated, and other basic changes.

It's too late for this code to be merged for the v6.6 kernel cycle but hopefully AMD P-State Preferred Core functionality will be ready to go come the Linux 6.7 cycle later this year.