AMD has slipped a new low-power CPU core type into Linux.
A new Linux kernel patch series posted to the kernel mailing list adds a “Low Power” CPU core type for AMD heterogeneous processors.
The x86 topology code in the Linux kernel already supports Performance and Efficiency core types.
Now AMD wants Linux to recognise a third category for heterogeneous platforms rather than shrugging and calling it “unknown”.
AMD engineer Vishal Badole said: “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”
There are no juicy details about how this low-power core differs from AMD’s existing efficiency or dense core type.
The only description is “a low-power core designed for minimal power consumption during background or idle workloads”.
The patch is tiny, adding about a dozen lines of code. It carries the new “low-power” core type from AMD’s Extended CPU Topology Core Type leaf into the Linux x86 topology plumbing.
That means Linux can report the core properly through its topology infrastructure instead of pretending it has found a mystery blob of silicon.
The patch series is now on the kernel mailing list for review.
