hosts/carbon: Set rps_cpus for ppp interface

hosts/carbon/ppp-ncfttb.nix

@@ -56,6 +56,46 @@
     ];
   };
 
+  environment.etc."ppp/ipv6-up" = {
+    text = ''
+      #! ${pkgs.runtimeShell} -e
+
+      ${pkgs.systemd}/bin/systemctl restart --no-block "ppp-setup-interface-queues@''${IFNAME}.service"
+      ${pkgs.systemd}/bin/systemctl restart --no-block ds-lite-dhcpcd.service
+    '';
+    mode = "555";
+  };
+
+  systemd.services."ppp-setup-interface-queues@".serviceConfig = let
+    setup-interface-queues = pkgs.clerie-build-support.writePythonScript {
+      name = "setup-interface-queues";
+      text = ''
+        import multiprocessing
+        from pathlib import Path
+        import sys
+
+        interface_name = sys.argv[1]
+
+        print(f"New ppp interface: {interface_name}")
+
+        num_cpus = multiprocessing.cpu_count()
+
+        print(f"Detected {num_cpus} cpus")
+
+        bitmask = "1" * num_cpus
+        hexmask = "{:x}".format(int(bitmask, 2))
+
+        rps_cpus = Path(f"/sys/class/net/{interface_name}/queues/rx-0/rps_cpus")
+        rps_cpus.write_text(hexmask)
+
+        print(f"Wrote hexmask {hexmask} to {rps_cpus}")
+      '';
+   };
+  in {
+    Type = "oneshot";
+    ExecStart = "${lib.getExe setup-interface-queues} %i";
+  };
+
   clerie.firewall.extraForwardMangleCommands = ''
     ip46tables -t mangle -A forward-mangle -p tcp --tcp-flags SYN,RST SYN -j TCPMSS --clamp-mss-to-pmtu
   '';