amd_pstate is a kernel module which implements support for AMD Ryzen P-states, offering more fine grained power management than ACPI C-states allow.
The amd_pstate kernel module has undergone changes since it was first implemented, and much of the documentation available is outdated.
If you have a system that you believe should have amd_pstate support but it isn't working you can try the following.
# if this prints `CpuDriver: amd_pstate` then amd_pstate is loaded
$ powerprofilesctl | grep Cpu | uniq
# try to load amd_pstate and the amd_pstate_ut test module in multiple ways
$ sudo modprobe amd_pstate dyndbg==pmf amd_pstate=guided amd_pstate.shared_mem=1 -v; sudo modprobe amd_pstate_ut -v
$ sudo dmesg | grep amd_pstate
amd_pstate:amd_pstate_init: amd_pstate: the _CPC object is not present in SBIOS
In this example we got an error saying the _CPC object is missing. Enable AMD CBS > NBIOS Common Options > SMU Common Options > CPPC > CPPC CTRL in your UEFI settings to fix it. If that option is not available, you may need to update your UEFI.
If instead the command above successfully loads amd_pstate, you may need to add a kernel param like amd_pstate=guided, or add the module name from above that worked to your list of modules to load. That's /etc/modules on most distros.
If everything is working correctly you should see something like this:
$ powerprofilesctl | grep Cpu | uniq
CpuDriver: amd_pstate
$ sudo dmesg | grep amd_pstate
[265365.656660] amd_pstate_ut: 1 amd_pstate_ut_acpi_cpc_valid success!
[265365.656664] amd_pstate_ut: 2 amd_pstate_ut_check_enabled success!
[265365.656807] amd_pstate_ut: 3 amd_pstate_ut_check_perf success!
[265365.656811] amd_pstate_ut: 4 amd_pstate_ut_check_freq success!
On earlier kernels without amd_pstate_ut you'll see a different success message.
My machine with a 7950x fails test 4 but amd_pstate otherwise seems to work.
[265365.656809] amd_pstate_ut: amd_pstate_ut_check_freq cpu0 cpudata_min_freq=400000 policy_min=3010000, they should be equal!
[265365.656811] amd_pstate_ut: 4 amd_pstate_ut_check_freq fail!
NixOS Config for amd_pstate
This snippet should turn on amd_pstate or get debug output about why it failed to load in dmesg.
If your kernel config is missing a required module it'll error.
boot = {
# _ut is for the debug warnings / self test
kernelModules = [ "amd_pstate" "amd_pstate_ut" ];
kernelParams = [
# mode selection required after cpufreq: amd-pstate: add amd-pstate driver parameter for mode selection
"amd_pstate=guided"
# sometimes necessary to stop acpi cpufreq loading first, should only be uncommented if you encounter that issue
# should only apply for <6.1 kernels
# "initcall_blacklist=acpi_cpufreq_init"
];
};
system.requiredKernelConfig = with config.lib.kernelConfig; [
(isYes "X86_AMD_PSTATE")
(isYes "X86_FEATURE_CPPC")
(isEnabled "X86_AMD_PSTATE_UT")
];
Abridged amd_pstate history
| Kernel Version | Change |
|---|---|
| 5.17 | Initial introduction of amd_pstate driver. shared_mem parameter required for support on most processors. |
| 6.1 | Introduction of amd_pstate driver parameter for mode selection (disabled/passive), split of amd_pstate_ut as a separate module, removal of shared_mem parameter |
| 6.3 | Addition of active mode (which corresponds to the amd_pstate_epp cpufreq driver) and guided mode |
| 6.5 | X86_AMD_PSTATE_DEFAULT_MODE Kconfig option added, and defaulted to 'active' |