AMD P-State Linux Patches Updated For Heterogeneous CPUs

Written by Michael Larabel in AMD on 11 June 2024 at 06:44 AM EDT. 2 Comments
Last month AMD Linux engineers posted ap atch series for better handling heterogeneous core type CPUs. This is for enhancing the P-State CPU frequency scaling on CPUs featuring a mix of conventional cores and efficiency cores, e.g. Zen 4 and Zen 4C. A third iteration of these patches were posted today.

AMD engineer Perry Yuan explains of this "amd_pstate" driver patch series:
"This patchset addresses critical issues and enhances performance settings for CPUs with heterogeneous core types in the AMD pstate driver. Specifically, it resolves problems related to calculating the highest performance and frequency on the latest CPUs with preferred cores. Additionally, the patchset includes documentation improvements in amd-pstate.rst, offering a comprehensive guide covering topics such as recommended reboot requirements during driver switching, debugging procedures for driver loading failures."

Most interesting of the series is this one for heterogeneous core topology for highest performance initialization:
"Introduces an optimization to the AMD-Pstate driver by implementing a heterogeneous core topology for the initialization of the highest performance value while driver loading. There are two type cores designed including performance core and Efficiency Core. Each core type has different highest performance and frequency values configured by the platform. The `amd_pstate` driver needs to identify the type of core to correctly set an appropriate highest perf value.

X86_FEATURE_HETERO_CORE_TOPOLOGY is used to identify whether the processor support heterogeneous core type by reading CPUID leaf Fn_0x80000026_EAX and bit 30. if the bit is set as one, then amd_pstate driver will check EBX 30:28 bits to get the core type."

With the v3 patches, additional code review has been carried out, they have been re-based against the latest Linux power management tree, more testing has completed, and various fixes.

AMD Ryzen CPUs

Hopefully we'll see these AMD P-State driver patches ready for the Linux v6.11 kernel cycle later this summer.
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