Switch to zen kernel optimized for znver4.

nix/configuration/hosts/odo/default.nix

@@ -3,6 +3,7 @@
   imports = [
     ./hardware-configuration.nix
     ./disk-config.nix
+    ./optimized_build.nix
   ];
 
   # Generate with `head -c4 /dev/urandom | od -A none -t x4`

nix/configuration/hosts/odo/optimized_build.nix

@@ -0,0 +1,30 @@
+{
+  config,
+  lib,
+  pkgs,
+  ...
+}:
+{
+  imports = [ ];
+
+  nixpkgs.overlays = [
+    (
+      self: super:
+      let
+        optimizeWithFlags =
+          pkg: flags:
+          pkg.overrideAttrs (old: {
+            NIX_CFLAGS_COMPILE = [ (old.NIX_CFLAGS_COMPILE or "") ] ++ flags;
+          });
+      in
+      {
+        linux_znver4 = optimizeWithFlags super.linux_zen [
+          "-march=znver4"
+          "-mtune=znver4"
+        ];
+      }
+    )
+  ];
+
+  boot.kernelPackages = lib.mkIf (!config.me.buildingIso) (pkgs.linuxPackagesFor pkgs.linux_znver4);
+}