AMD P-State Patches Updated But Miss The Linux 6.0 Merge Window

Written by Michael Larabel in AMD on 15 August 2022 at 06:04 AM EDT. 7 Comments
AMD today sent out revised patches for improving the AMD P-State CPU frequency scaling Linux driver that aims to provide better power efficiency than the generic ACPI CPUFreq driver that has long been relied upon for AMD processors.

The AMD P-State driver continues to see improvements after the initial code mainlined back in Linux 5.17 has been problematic for some, in some workloads leading to noticeably lower performance than acpi-cpufreq, etc. AMD P-State is for Zen 2 and newer CPUs due to its dependence on ACPI CPPC support.

Recently AMD has been working on precision boost control and other fixes to AMD P-State and that's the patches revised today. Those patches for the precision boost hardware control and fixes were sent out today in their fifth revision.
This patchsets adds support for precision boost hardware control for AMD processors.

Meanwhile the patchset fixes lowest perf query and desired perf scope issues. Update transition delay and latency default value to meet SMU firmware requirement. and do some code cleanups, It also exports cpufreq cpu release and acquire for coming amd-pstate epp mode driver

The patch series are tested on the AMD mobile and EYPC server systems.

The v5 patches are now available for testing. However, given the timing this material has now missed out on the Linux 6.0 merge window. So at least the feature work won't be merged until at least Linux 6.1 while we'll see if the fixes are sent in sooner. But given that the fixes portion of the work has already been sitting on the mailing list for weeks, it doesn't appear that AMD is in any rush for sending it in early.

Separately, sent out today was a different AMD P-State fix. There is a fix for reading the highest performance value state with the amd_pstate driver. Due to "new AMD processors" (presumably Zen 4), the wrong highest performance state can be read by this driver. The patch fixes that up to avoid the wrong calculation on these upcoming AMD CPUs. Hopefully that patch will get picked up and back-ported soon for ensuring Zen 4 CPUs can work nicely on the amd_pstate kernel driver.
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