machine_setup/nix/configuration/roles/optimized_build/default.nix

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

{
  imports = [ ];

  options.me = {
    optimizations.enable = lib.mkOption {
      type = lib.types.bool;
      default = false;
      example = true;
      description = "Whether we want to enable CPU optimizations (will trigger a rebuild from source).";
    };

    optimizations.arch = lib.mkOption {
      type = lib.types.str;
      default = null;
      example = "znver4";
      description = "The CPU arch for which programs should be optimized.";
    };

    optimizations.system_features = lib.mkOption {
      type = lib.types.listOf lib.types.str;
      default = [ ];
      example = [
        "gccarch-znver4"
        "gccarch-znver5"
        "gccarch-skylake"
        # "gccarch-alderlake" missing WAITPKG
        "gccarch-x86-64-v3"
        "gccarch-x86-64-v4"
        "benchmark"
        "big-parallel"
        "kvm"
        "nixos-test"
      ];
      description = "The list of CPU features that should be enabled on this machine.";
    };
  };

  config = lib.mkMerge [
    (lib.mkIf (!config.me.optimizations.enable) (
      lib.mkMerge [
        {
          boot.kernelPackages = pkgs.linuxPackagesFor pkgs.linux_6_14;
        }
      ]
    ))
    (lib.mkIf config.me.optimizations.enable (
      lib.mkMerge [
        {
          boot.kernelPackages = pkgs.linuxPackagesFor pkgs.linux_me;

          nixpkgs.hostPlatform = {
            gcc.arch = config.me.optimizations.arch;
            gcc.tune = config.me.optimizations.arch;
            system = "x86_64-linux";
          };

          # Uncomment on of these to enable cross compiling:
          # nixpkgs.buildPlatform = builtins.currentSystem;
          # nixpkgs.buildPlatform = {
          #   gcc.arch = "znver4";
          #   gcc.tune = "znver4";
          #   system = "x86_64-linux";
          # };

          nixpkgs.overlays = [
            (
              final: prev:
              let
                addConfig =
                  additionalConfig: pkg:
                  pkg.override (oldconfig: {
                    structuredExtraConfig = pkg.structuredExtraConfig // additionalConfig;
                  });
              in
              {
                linux_me = addConfig {
                  # Full preemption
                  PREEMPT = lib.mkOverride 60 lib.kernel.yes;
                  PREEMPT_VOLUNTARY = lib.mkOverride 60 lib.kernel.no;

                  # Google's BBRv3 TCP congestion Control
                  TCP_CONG_BBR = lib.kernel.yes;
                  DEFAULT_BBR = lib.kernel.yes;

                  # Preemptive Full Tickless Kernel at 300Hz
                  HZ = lib.kernel.freeform "300";
                  HZ_300 = lib.kernel.yes;
                  HZ_1000 = lib.kernel.no;
                } prev.linux_6_14;
              }
            )
            (final: prev: {
              haskellPackages = prev.haskellPackages.extend (
                final': prev': {
                  inherit (pkgs-unoptimized.haskellPackages)
                    crypto-token
                    crypton
                    crypton-connection
                    crypton-x509
                    crypton-x509-store
                    crypton-x509-system
                    crypton-x509-validation
                    hspec-wai
                    http-client-tls
                    http2
                    pandoc
                    pandoc-cli
                    pandoc-lua-engine
                    pandoc-server
                    servant-server
                    tls
                    wai-app-static
                    wai-extra
                    warp
                    ;
                }
              );
            })
            (final: prev: {
              inherit (pkgs-unoptimized)
                gsl
                redis
                valkey
                ;
            })
          ];
        }
      ]
    ))
    (lib.mkIf (config.me.optimizations.system_features != [ ]) (
      lib.mkMerge [
        {
          nix.settings.system-features = lib.mkForce config.me.optimizations.system_features;
        }
      ]
    ))

  ];
}