nixos/gnome: Remove realtime scheduling option

It is now accomplished using rtkit rather than setcap wrapper: https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2060 Replace the option with `security.rtkit.enable`. Closes: #90201 Closes: #86730
NixOS · Feb 27, 2022 · 0426898 · 0426898
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diff --git a/nixos/doc/manual/from_md/release-notes/rl-2205.section.xml b/nixos/doc/manual/from_md/release-notes/rl-2205.section.xml
@@ -421,6 +421,16 @@
           6.x</link> and renamed to <literal>gnome-secrets</literal>.
         </para>
       </listitem>
+      <listitem>
+        <para>
+          <literal>services.gnome.experimental-features.realtime-scheduling</literal>
+          option has been removed, as GNOME Shell now
+          <link xlink:href="https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2060">uses
+          rtkit</link>. Use
+          <literal>security.rtkit.enable = true;</literal> instead. As
+          before, you will need to have it enabled using GSettings.
+        </para>
+      </listitem>
       <listitem>
         <para>
           If you previously used

diff --git a/nixos/doc/manual/release-notes/rl-2205.section.md b/nixos/doc/manual/release-notes/rl-2205.section.md
@@ -138,6 +138,8 @@ In addition to numerous new and upgraded packages, this release has the followin
 
 - The `gnome-passwordsafe` package updated to [version 6.x](https://gitlab.gnome.org/World/secrets/-/tags/6.0) and renamed to `gnome-secrets`.
 
+- `services.gnome.experimental-features.realtime-scheduling` option has been removed, as GNOME Shell now [uses rtkit](https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2060). Use `security.rtkit.enable = true;` instead. As before, you will need to have it enabled using GSettings.
+
 - If you previously used `/etc/docker/daemon.json`, you need to incorporate the changes into the new option `virtualisation.docker.daemon.settings`.
 
 - Ntopng (`services.ntopng`) is updated to 5.2.1 and uses a separate Redis instance if `system.stateVersion` is at least `22.05`. Existing setups shouldn't be affected.

diff --git a/nixos/modules/services/x11/desktop-managers/gnome.nix b/nixos/modules/services/x11/desktop-managers/gnome.nix
@@ -132,6 +132,10 @@ in
       [ "environment" "gnome3" "excludePackages" ]
       [ "environment" "gnome" "excludePackages" ]
     )
+    (mkRemovedOptionModule
+      [ "services" "gnome" "experimental-features" "realtime-scheduling" ]
+      "Set `security.rtkit.enable = true;` to make realtime scheduling possible. (Still needs to be enabled using GSettings.)"
+    )
   ];
 
   options = {
@@ -142,38 +146,6 @@ in
       core-utilities.enable = mkEnableOption "GNOME core utilities";
       core-developer-tools.enable = mkEnableOption "GNOME core developer tools";
       games.enable = mkEnableOption "GNOME games";
-
-      experimental-features = {
-        realtime-scheduling = mkOption {
-          type = types.bool;
-          default = false;
-          description = ''
-            Makes mutter (which propagates to gnome-shell) request a low priority real-time
-            scheduling which is only available on the wayland session.
-            To enable this experimental feature it requires a restart of the compositor.
-            Note that enabling this option only enables the <emphasis>capability</emphasis>
-            for realtime-scheduling to be used. It doesn't automatically set the gsetting
-            so that mutter actually uses realtime-scheduling. This would require adding <literal>
-            rt-scheduler</literal> to <literal>/org/gnome/mutter/experimental-features</literal>
-            with dconf-editor. You cannot use extraGSettingsOverrides because that will only
-            change the default value of the setting.
-
-            Please be aware of these known issues with the feature in nixos:
-            <itemizedlist>
-             <listitem>
-              <para>
-               <link xlink:href="https://github.com/NixOS/nixpkgs/issues/90201">NixOS/nixpkgs#90201</link>
-              </para>
-             </listitem>
-             <listitem>
-              <para>
-               <link xlink:href="https://github.com/NixOS/nixpkgs/issues/86730">NixOS/nixpkgs#86730</link>
-              </para>
-            </listitem>
-            </itemizedlist>
-          '';
-        };
-      };
     };
 
     services.xserver.desktopManager.gnome = {
@@ -480,29 +452,6 @@ in
       ];
     })
 
-    # Enable soft realtime scheduling, only supported on wayland
-    (mkIf serviceCfg.experimental-features.realtime-scheduling {
-      security.wrappers.".gnome-shell-wrapped" = {
-        source = "${pkgs.gnome.gnome-shell}/bin/.gnome-shell-wrapped";
-        owner = "root";
-        group = "root";
-        capabilities = "cap_sys_nice=ep";
-      };
-
-      systemd.user.services.gnome-shell-wayland = let
-        gnomeShellRT = with pkgs.gnome; pkgs.runCommand "gnome-shell-rt" {} ''
-          mkdir -p $out/bin/
-          cp ${gnome-shell}/bin/gnome-shell $out/bin
-          sed -i "s@${gnome-shell}/bin/@${config.security.wrapperDir}/@" $out/bin/gnome-shell
-        '';
-      in {
-        # Note we need to clear ExecStart before overriding it
-        serviceConfig.ExecStart = ["" "${gnomeShellRT}/bin/gnome-shell"];
-        # Do not use the default environment, it provides a broken PATH
-        environment = mkForce {};
-      };
-    })
-
     # Adapt from https://gitlab.gnome.org/GNOME/gnome-build-meta/blob/gnome-3-38/elements/core/meta-gnome-core-utilities.bst
     (mkIf serviceCfg.core-utilities.enable {
       environment.systemPackages =