AMD Linux Patches Introduce New "Low Power" CPU Core Type

A new Linux kernel patch series posted to the kernel mailing list minutes ago is introducing a new "Low Power" CPU core type for AMD heterogeneous processors. The x86 topology code in the Linux kernel already supports the notion of Performance and Efficiency type cores while now a new "Low Power" core type is being introduced for AMD heterogeneous platforms.

AMD engineer Vishal Badole commented on the Linux kernel patch cover letter of this new Low Power core type:

"This series extends the x86 topology cpu_type classification to support a Low Power core type, in addition to the existing Performance and Efficiency types.

AMD heterogeneous parts report the core type via CPUID Fn0x80000026 EBX[31:28] (Extended CPU Topology, Core Type). Value 2 identifies a low-power core designed for minimal power consumption during background or idle workloads. Distinguishing it from a regular efficiency core matters for:

- user space exposure via /sys/kernel/debug/x86/topo/cpus/*, which today reports cpu_type "unknown" for low-power cores

- amd_get_boost_ratio_numerator(): on every X86_FEATURE_AMD_HTR_CORES-capable AMD/Hygon part, low-power cores must scale by amd_get_highest_perf() rather than the fixed CPPC_HIGHEST_PERF_PERFORMANCE ceiling, matching the existing efficiency-core path"

No other details relative to the existing AMD efficiency (dense) core type besides the "a low-power core designed for minimal power consumption during background or idle workloads". The dozen new lines of code are just propagating the new "low-power" core type from the AMD Extended CPU Topology, Core Type leaf and properly reporting it now through the Linux x86 topology infrastructure.

This new AMD Linux patch series for the Low Power CPU core type can be found on the kernel mailing list where it's now undergoing review.

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