native opts go nyoom

machines/levitation/configuration.nix

@@ -74,7 +74,8 @@
   # Configure nix build
   nix.settings = {
     cores = 8;
-    max-jobs = 8;
+    max-jobs = 6;
+    system-features = [ "gccarch-znver3" ];
   };
 
   # Calibre
@@ -90,4 +91,37 @@
       enableBookUploading = true;
     };
   };
+
+  nixpkgs = {
+    # Native opts go nyoom
+    localSystem = {
+      gcc = {
+        arch = "znver3";
+        tune = "znver3";
+      };
+      system = "x86_64-linux";
+    };
+    # Fix some packages that are broken on nixos-21.11 with march=znver3
+    # We'll substitute these with the version from a second import of nixpkgs without the gcc
+    # configuration.
+    overlays = [
+      (self: super:
+        let
+          vanilla-pkgs = import inputs.nixpkgs-unstable {
+            system = "x86_64-linux";
+            config = {
+              localSystem = {
+                gcc = {
+                  arch = null;
+                  tune = null;
+                };
+              };
+            };
+          };
+        in {
+          libxcrypt = vanilla-pkgs.libxcrypt;
+          perl = vanilla-pkgs.perl;
+        })
+    ];
+  };
 }