Nixpkgs: Cannot set default cpu frequency governor

[fdietze]

Issue description

I have the following in my configuration.nix:

  powerManagement = {
    enable = true;
    cpuFreqGovernor = "powersave";
  };

But when I boot, the governor is set to performance

Technical details

• system: "x86_64-linux"
• host os: Linux 4.19.57, NixOS, 19.03.173052.aef662d2eb5 (Koi)
• multi-user?: yes
• sandbox: yes
• version: nix-env (Nix) 2.2.2
• channels(felix): "nixpkgs-19.09pre184359.73392e79aa6"
• channels(root): "nixos-19.03.173052.aef662d2eb5, nixos-hardware, nixpkgs-unstable-19.09pre182717.b58ada326aa"
• nixpkgs: /home/felix/.nix-defexpr/channels/nixpkgs

[xaverdh]

Is there anything in the journal / kernel logs related to this?
What does systemctl status cpufreq.service say?
cat /sys/bus/cpu/devices/cpu*/cpufreq/scaling_available_governors might be useful as well, to see what governors are supported on your system.

[fdietze]

$ cat /sys/bus/cpu/devices/cpu*/cpufreq/scaling_available_governors
performance powersave
performance powersave
performance powersave
performance powersave
performance powersave
performance powersave
performance powersave
performance powersave

Ah! This might be the issue:

$ systemctl status cpufreq.service
Unit cpufreq.service could not be found.

[xaverdh]

Ok, that service should be enabled according to your config.

Stupid question: you did rebuild your system configuration, right?

Also there usually is an entry powerManagement.cpuFreqGovernor = lib.mkDefault [..] in hardware-configuration.nix, does that exist?

[GRBurst]

I have the same issue.
In my hardware configuration that entry exists and the governor is set to "powersave" as well (same as in my configuration.nix.
But it is not applied.

Unit does not exist:

$ systemctl status cpufreq.service
Unit cpufreq.service could not be found.

$ systemctl --user status cpufreq.service
Unit cpufreq.service could not be found.

[GRBurst]

cpupower confirms that my cpu supports "powersave" governor:

$ cpupower frequency-info
analyzing CPU 0:
  driver: intel_pstate
  CPUs which run at the same hardware frequency: 0
  CPUs which need to have their frequency coordinated by software: 0
  maximum transition latency:  Cannot determine or is not supported.
  hardware limits: 400 MHz - 4.00 GHz
  available cpufreq governors: performance powersave
  current policy: frequency should be within 400 MHz and 4.00 GHz.
                  The governor "performance" may decide which speed to use
                  within this range.
  current CPU frequency: Unable to call hardware
  current CPU frequency: 3.72 GHz (asserted by call to kernel)
  boost state support:
    Supported: yes
    Active: yes

Setting in manually with cpupower does work.

Therefore I guess it is the cpufreq service and not a configurational thing.

[xaverdh]

Ah yes, happens to me as well now. ~One~ ~of~ ~my~ ~boxes~ ~hasn't~ ~upgraded~ ~yet~ ~and~ ~is~ ~fine~ ~on~ ~nixos-19.09pre184759.88c2586958,~ ~the~ ~other~ ~has~ ~(to~ ~nixos-19.09pre184855.beff2f8d75e)~ ~and~ ~exhibits~ ~this~ ~bug.~ ~So~ ~it~ ~was~ ~likely~ ~introduced~ ~between~ ~those.~

[xaverdh]

Hmm it appears that the machine in question did not have a default for the governor set in hardware-configuration.nix.
After setting it explicitly, it does work.

[fdietze]

Stupid question: you did rebuild your system configuration, right?

Yes, I did. :wink:

Also there usually is an entry powerManagement.cpuFreqGovernor = lib.mkDefault [..] in
hardware-configuration.nix, does that exist?

I removed it. It was set to performance. Should it make a difference? Should I add it again?

[xaverdh]

No, explicitly setting powerManagement.cpuFreqGovernor should be sufficient.

[lheckemann]

What does nixos-option powerManagement.cpuFreqGovernor say?

[fdietze]

❯ nixos-option powerManagement.cpuFreqGovernor
Value:
null

Default:
null

Example:
"ondemand"

Description:

"Configure the governor used to regulate the frequence of the\navailable CPUs. By default, the kernel configures the\nperformance governor, although this may be overwritten in your\nhardware-configuration.nix file.\n\nOften used values: \"ondemand\", \"powersave\", \"performance\"\n"

Declared by:
  "/home/felix/.nix-defexpr/channels/nixpkgs/nixos/modules/tasks/cpu-freq.nix"

Defined by:
  "/nix/var/nix/profiles/per-user/root/channels/nixos-hardware/common/pc/laptop"

[lheckemann]

Aah, so it turns out that nixos-hardware disables the setting if tlp is enabled:

https://github.com/NixOS/nixos-hardware/blob/54268d11ae4e7a35e6085c5561a8d585379e5c73/common/pc/laptop/default.nix#L6-L10

So either disabling tlp or configuring tlp itself to set the governor you want should fix the problem.

[fdietze]

Does powerManagement.enable = true enable tlp somehow? I didn't enable it explicitly in my config.

[lheckemann]

No, but nixos-hardware's laptop profile does.

[GRBurst]

Aah, so it turns out that nixos-hardware disables the setting if tlp is enabled:

https://github.com/NixOS/nixos-hardware/blob/54268d11ae4e7a35e6085c5561a8d585379e5c73/common/pc/laptop/default.nix#L6-L10

So either disabling tlp or configuring tlp itself to set the governor you want should fix the problem.

Hey,
thanks - enabling tlp in the nixos configuration.nix and providing some extraConfigs like setting the governor seems to work as expected.

It may be worth to add a hint in to the powerManagement and / or powerManagement.cpuFreqGovernor settings ;-)

[GRBurst]

      extraConfig = ''
        tlp_DEFAULT_MODE=BAT
        CPU_SCALING_GOVERNOR_ON_BAT=powersave
      '';

[stale[bot]]

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