Troubleshooting
From NixOS Wiki
This article explains some methods for general troubleshooting. For application specific issues, please reference the particular wiki page for that program.
My system is slow!
Check your /etc/nixos/hardware-configuration.nix. There probably is a line which looks something like this:
powerManagement.cpuFreqGovernor = lib.mkDefault "powersave";
Change the value inside quotation marks (in this case "powersave") to be "performance".
The new line should look like this:
powerManagement.cpuFreqGovernor = lib.mkDefault "performance";
If the line didn't exist, add it there yourself.