One of the many changes to look forward to with the upcoming [1]Linux 6.13 kernel cycle is the [2]AMD P-State driver to be [3]used by default with the new EPYC 9005 series processors . While AMD Ryzen CPUs for a while now have been defaulting to the modern AMD P-State driver that makes use of ACPI CPPC platform support for allowing better power efficiency, AMD EPYC CPUs have kept to using the generic ACPI CPUFreq frequency scaling driver. But now AMD engineers have deemed amd_pstate ready for use with [4]EPYC 9005 "Turin" CPUs and will be the default choice moving forward. Here is more information and power/performance benchmarks for this shift while testing using the EPYC 9755 processors.

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It was just last month that AMD engineers posted patches to [6]enable AMD P-State by default with EPYC 9005 series processors . Those patches have since been queued up into the Linux power management subsystem's "-next" branch ahead of the Linux 6.13 merge window kicking off next week. Thus beginning with Linux 6.13 -- which will be out as stable around late January or early February -- those using the new 5th Gen AMD EPYC processors will find AMD P-State by default. Those wanting to stick to using the ACPI CPUFreq driver for whatever reason can use "amd_pstate=disable" on the kernel command-line to override the default.

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This default change is being made just for EPYC 9005 series and moving forward. AMD EPYC 7002/7003/8004/9004 series processors can always opt-in manually to using AMD P-State instead of ACPI CPUFreq, but only with the EPYC 9005 series is this now validated by AMD. It turns out EPYC Turin / Zen 5 does contain enhancements to its design for benefiting AMD P-State usage. With these EPYC Turin CPUs the AMD P-State "active" mode is the default.

While during the development stages of the amd_pstate driver I ran many benchmarks on Ryzen, I was curious to run some new EPYC benchmarks with the AMD P-State driver. Recently I carried out some testing on the AMD Volcano server with dual EPYC 9755 (128-core Zen 5 per socket) processors while running a build of the Linux 6.12-rc4 development kernel with the EPYC amd_pstate patches applied. The following CPU frequency driver / governor combinations were tested:

acpi-cpufreq schedutil - The default/out-of-the-box state for EPYC Zen 5 on Ubuntu 24.04 LTS... The ACPI CPUFreq governor with the Schedutil governor.

acpi-cpufreq performance - ACPI CPUFreq but switching to the "performance" governor that is very common for servers and especially the HPC world for ensuring maximum performance.

amd-pstate-epp powersave, EPP power - The new default/out-of-the-box state of using AMD P-State on Linux 6.13+. This is with the "powersave" governor used by default there rather than "schedutil". The Energy Performance Preference (EPP) was also set to the "power" mode.

amd-pstate-epp performance - The AMD P-State default moving forward for Linux 6.13+ while switching to the "performance" governor akin to the "acpi-cpufreq performance" common use currently with EPYC servers. The EPP there is "performance".

From there a variety of benchmarks/workloads were tested while also monitoring the combined EPYC 9755 CPU power consumption, CPU0 temperature, and CPU peak frequency for each of the benchmarks conducted.



[1] https://www.phoronix.com/search/Linux+6.13

[2] https://www.phoronix.com/search/AMD+P-State

[3] https://www.phoronix.com/news/AMD-P-State-EPYC-Linux-6.13

[4] https://www.phoronix.com/search/EPYC+9005

[5] https://www.phoronix.com/image-viewer.php?id=amd-epyc-9005-pstate&image=amd_epyc_pstate1_lrg

[6] https://www.phoronix.com/news/AMD-P-State-EPYC-Linux-Patches

[7] https://www.phoronix.com/image-viewer.php?id=amd-epyc-9005-pstate&image=amd_epyc_pstate2_lrg