nixpkgs/nixos/modules/services/hardware/throttled.nix

{ config, lib, pkgs, ... }:

with lib;

let
  cfg = config.services.throttled;
in {
  options = {
    services.throttled = {
      enable = mkEnableOption (lib.mdDoc "fix for Intel CPU throttling");

      extraConfig = mkOption {
        type = types.str;
        default = "";
        description = lib.mdDoc "Alternative configuration";
      };
    };
  };

  config = mkIf cfg.enable {
    systemd.packages = [ pkgs.throttled ];
    # The upstream package has this in Install, but that's not enough, see the NixOS manual
    systemd.services.throttled.wantedBy = [ "multi-user.target" ];

    environment.etc."throttled.conf".source =
      if cfg.extraConfig != ""
      then pkgs.writeText "throttled.conf" cfg.extraConfig
      else "${pkgs.throttled}/etc/throttled.conf";

    # Kernel 5.9 spams warnings whenever userspace writes to CPU MSRs.
    # See https://github.com/erpalma/throttled/issues/215
    boot.kernelParams =
      optional (versionAtLeast config.boot.kernelPackages.kernel.version "5.9")
      "msr.allow_writes=on";
  };
}