Linux Gets Fix For AMD Zen 3 CPU Frequency Handling Stemming From 8 Year Old Workaround
Written by Michael Larabel in AMD on 24 October 2020 at 06:47 AM EDT. 4 Comments
AMD --
Since 2012 there has been a quirk in the Linux kernel to disable/override using ACPI _PSD data on all AMD processors as a workaround in turn for Windows-specific behavior that clashes with the semantics of the Linux ACPI CPUFreq driver for CPU frequency scaling. With AMD Zen 3 this quirk is no longer needed to behave correctly and thus Linux 5.10 is going to drop this eight year old quirk on Zen 3 and newer.

The change since 2012 in the Linux kernel for AMD CPUs has overrode the ACPI _PSD table supplied by the BIOS. But now for Family 19h / Zen 3, the table accurately reports the P-state dependency of CPU cores. That correct table is needed for proper CPU frequency control with the new processors and thus the new kernel will stop overriding it so it can be used by ACPI CPUfreq for its frequency handling on the shiny new CPUs.

This change was sent in as part of additional power management updates for the Linux 5.10 kernel.

Given that it's a "fix" and amounts to just changing around one line of code (only applying the override for CPUs less than Family 19h), it will hopefully be back-ported quickly to stable kernel series ahead of the AMD Ryzen 5000 series beginning to ship in early November.
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