Laptop

Power management

NixOS has several tools to help you manage the power on your system and it also has a stock feature for power management. To enable the stock NixOS power management tool which allows for managing hibernate and suspend states you can write powerManagement.enable = true;. This tool is compatible with the other tools mentioned, but the other tools may overwrite this setting.

CPU performance scaling

thermald

Thermald proactively prevents overheating on Intel CPUs and works well with other tools. Enabled by: services.thermald.enable = true;

tlp

A common tool used to save power on laptops is tlp, which has sensible defaults for most laptops. To enable tlp you simply just write services.tlp.enable = true; in your configuration.nix. However, if you need a specific configuration, you can do as shown in the example below.

services.tlp = {
      enable = true;
      settings = {
        CPU_SCALING_GOVERNOR_ON_AC = "performance";
        CPU_SCALING_GOVERNOR_ON_BAT = "powersave";

        CPU_ENERGY_PERF_POLICY_ON_BAT = "power";
        CPU_ENERGY_PERF_POLICY_ON_AC = "performance";

        CPU_MIN_PERF_ON_AC = 0;
        CPU_MAX_PERF_ON_AC = 100;
        CPU_MIN_PERF_ON_BAT = 0;
        CPU_MAX_PERF_ON_BAT = 20;

       #Optional helps save long term battery health
       START_CHARGE_THRESH_BAT0 = 40; # 40 and bellow it starts to charge
       STOP_CHARGE_THRESH_BAT0 = 80; # 80 and above it stops charging

      };
};

This example enables tlp and sets the minimum and maximum frequencies for the CPU based on whether it is plugged into power or not. It also changes the CPU scaling governor based on this.

auto-cpufreq

Another tool used for power management is auto-cpufreq which aims to replace tlp. When using auto-cpufreq it is therefore recommended to disable tlp as these tools are conflicting with each other. However, NixOS does allow for using both at the same time, and you can therefore run them in tandem at your own risk. To enable the service, add services.auto-cpufreq.enable = true; to your configuration.nix.

Example of how to configure auto-cpufreq:

services.auto-cpufreq.enable = true;
services.auto-cpufreq.settings = {
  battery = {
     governor = "powersave";
     turbo = "never";
  };
  charger = {
     governor = "performance";
     turbo = "auto";
  };
};

Powertop

Powertop is a power analysis tool, but it also has a feature called auto-tune which will enable power saving settings on your device. These power saving settings should be almost the same as those enabled by tlp, although powertop enables USB auto-suspend by default. This can make your input devices such as the keyboard unresponsive for some time when it has been suspended. To enable powertop: powerManagement.powertop.enable = true;. This also enables the auto-tune feature of powertop.

Hardware support

Hybrid graphics

Many laptops have both a dedicated and a discrete GPU. To use your laptop effectively you have to manage both GPUs. For guidance on how to configure the GPUs, refer to the dedicated wiki-pages for your configuration. If you want to have the option to run your laptop with and without the discrete GPU to save power, you can either disable it in the bios (if possible) or you can use Nix's feature to define specialisations to give you two boot entries on each rebuild of your system.

Example of a nvidia specialisation:

specialisation = { 
   nvidia.configuration = { 
     # Nvidia Configuration 
     services.xserver.videoDrivers = [ "nvidia" ]; 
     hardware.graphics.enable = true; 
  
     # Optionally, you may need to select the appropriate driver version for your specific GPU. 
     hardware.nvidia.package = config.boot.kernelPackages.nvidiaPackages.stable; 
  
     # nvidia-drm.modeset=1 is required for some wayland compositors, e.g. sway 
     hardware.nvidia.modesetting.enable = true; 
  
     hardware.nvidia.prime = { 
       sync.enable = true; 
  
       # Bus ID of the NVIDIA GPU. You can find it using lspci, either under 3D or VGA 
       nvidiaBusId = "PCI:1:0:0"; 
  
       # Bus ID of the Intel GPU. You can find it using lspci, either under 3D or VGA 
       intelBusId = "PCI:0:2:0"; 
     };
  };
};

Troubleshooting

Laptop runs hot when on power, but not on battery

If you use tlp and experience this issue a solution can be to tell tlp to always run in battery mode.

services.tlp = {
    enable = true;
    settings = {
      TLP_DEFAULT_MODE = "BAT";
      TLP_PERSISTENT_DEFAULT = 1;
    };
 };

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