epyc: init hydra settings properly

modules/nix-daemon.nix

@@ -42,13 +42,17 @@ in
       package = pkgs.nixVersions.nix_2_13;
 
       # should be enough?
-      nrBuildUsers = lib.mkDefault 32;
+      nrBuildUsers = 128;
 
       # https://github.com/NixOS/nix/issues/719
+      daemonCPUSchedPolicy = "batch";
+      daemonIOSchedClass = "best-effort";
+      daemonIOSchedPriority = 5;
 
       settings = {
         keep-outputs = true;
         keep-derivations = true;
+        max-jobs = 64;
         # in zfs we trust
         fsync-metadata = lib.boolToString (!config.boot.isContainer or config.fileSystems."/".fsType != "zfs");
         substituters = [