AMD Heterogeneous CPU Design Topology Patches Coming For Linux 6.13

The latest patches from AMD Linux engineers for working on x86 heterogeneous design identification were queued last week for introduction in the Linux 6.13 kernel.

The x86 Heterogeneous design identification patch series was queued last week into tip/tip.git's "x86/cpu" Git branch, thereby making it material for adding to the Linux 6.13 merge window barring any last minute issues from coming to light. As explained there by AMD Linux engineer Mario Limonciello:

"This series adds topology identification for Intel and AMD processors and uses this identification in the AMD CPPC code to identify the boost numerator.

This series was previously submitted as, but this was based on some patches in linux-pm/linux-next that will be dropped.

Instead the series is now based on tip/master.

This also pulls one patch from Pawan's series and adjusts it for all feedback while adding AMD support at the same time."

As part of the patch series is the patch to use the heterogeneous core topology for identifying the boost numerator:

"AMD heterogeneous designs include two types of cores:
* Performance
* Efficiency

Each core type has different highest performance values configured by the platform. Drivers such as `amd_pstate` need to identify the type of core to correctly set an appropriate boost numerator to calculate the maximum frequency.

X86_FEATURE_AMD_HETEROGENEOUS_CORES is used to identify whether the SoC supports heterogeneous core type by reading CPUID leaf Fn_0x80000026.

On performance cores the scaling factor of 196 is used. On efficiency cores the scaling factor is the value reported as the highest perf. Efficiency cores have the same preferred core rankings."

Another patch added to tip/tip.git's x86/cpu branch is for introducing the AMD Workload Classification feature bit. This indicates whether the CPU supports workload-based heuristic feedback to the OS for scheduling decisions.

These patches are just the latest in long running work going on months for better optimizing current and future AMD processors that feature a mix of classic (performance) and dense (efficiency) CPU cores for better power and performance handling under Linux.

The Linux 6.13 merge window will be opening up during the back half of November while the stable kernel will be out in February.