AMD P-State v4 Linux Testing On A Ryzen 5 5500U

Written by Michael Larabel in Software on 24 November 2021 at 09:15 AM EST. Page 1 of 5. 14 Comments.

With AMD having published a new revision to their AMD P-State Linux CPU frequency scaling driver that they are working towards mainlining with a goal of better power efficiency on Linux, here are some initial benchmarks of that new patch series when using a Ryzen 5 5500U notebook.

The amd-pstate driver was updated a fourth time this past week since its unveiling in September with a goal of delivering better performance / power efficiency over the generic ACPI CPUFreq driver used on Linux systems. AMD's P-State driver makes use of ACPI CPPC that is supported on Zen 2 and newer processors for making more precise handling and better informed decisions around ramping up/down the performance state of the processor.

As of Linux 5.16 this driver hasn't been merged to mainline yet but is actively worked on by AMD and their partners at Valve, etc. For this initial amd-pstate v4 benchmarking I was using a Ryzen 5 5500U laptop as a reference platform and one that is properly supported by this driver. The amd-pstate driver currently works for a variety of Zen 2 and Zen 3 mobile systems and desktops and servers but not universally supported yet. On some Zen 3 systems even with ACPI CPPC and other features enabled from the BIOS, the amd-pstate driver is not yet compatible -- for those wanting to try out these driver patches, it is known immediately at module load time whether or not the system is compatible.

This testing was with the AMD Ryzen 5 5500U at stock speeds within a Lenovo IdeaPad laptop. Note the same clock speed configuration was used throughout testing -- the different frequency reported in the system table amounts to whether the base or turbo frequency is exposed via sysfs and then auto-recorded by the Phoronix Test Suite.

AMD P-State Linux Driver vs. CPUFreq Testing

A wide variety of benchmarks were run on this AMD laptop while benchmarking both acpi-cpufreq and amd-pstate from the same Linux 5.15 based kernel. On both CPU frequency scaling drivers, the ondemand, powersave, schedutil, and performance governors were benchmarked. During the benchmarks the CPU power consumption exposed via the RAPL interface was monitored along with the SoC temperature. Tests on more AMD processors with the amd-pstate driver will come once development appears more settled and en route to the mainline tree.

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