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limiting resources used by nix builds

2 min read

  # shedule nix builds with low priority, so the laptop is still usable while building something
  nix.daemonCPUSchedPolicy = "idle";
  nix.daemonIOSchedClass = "idle";
  systemd.services.nix-daemon.serviceConfig.CPUSchedulingPolicy = lib.mkForce "idle";
  systemd.services.nix-daemon.serviceConfig.IOSchedulingPriority = lib.mkForce "idle";
  systemd.services.nix-daemon.serviceConfig.CPUQuota = lib.mkForce "100%";
  systemd.services.nix-daemon.serviceConfig.CPUWeight= lib.mkForce "idle";
  systemd.services.nix-daemon.environment = {
    LD_PRELOAD = "${pkgs.trickle}/lib/trickle/trickle-overload.so";
    TRICKLE_WINDOW_SIZE = "200";
    TRICKLE_UPLOAD_LIMIT = "10";
    TRICKLE_LSMOOTH = "20";
    TRICKLE_VERBOSE = "0";
    TRICKLE_SOCKNAME = "";
    TRICKLE_ARGV = "alacritty";
    TRICKLE_TSMOOTH = "3.0";
    TRICKLE_DOWNLOAD_LIMIT = "30";
  };
  nix.extraOptions = ''
    download-speed = 30
  '';

  • the serviceConfig does not make it into the [Service] section of ${github:c2vi/nixos#top.main}/etc/systemd/system/nix-daemon.service but rather ${github:c2vi/nixos#top.main}/etc/systemd/system/nix-daemon.service.d/overrides.conf… i thought there was a bug, that my serviceConfig was somehow ignored by NixOS…

  • this has the service config as text: nix eval '.#nixosConfigurations.main.config.systemd.units."nix-daemon.service".text' --raw

    • also i used: nix eval .#nixosConfigurations.main.config.environment.etc.systemd/system.source --impure

  • i tried trickle (pkg) to limit

  • the command to finally run the nix build (for the whole system-update) slowly while using the laptop: sudo -E nix build .#top.main --impure --store / --option download-speed 30 --max-jobs 1 --cores 1 --option http-connections 1 --builders "$mosatop" -v

    • rel: Run a Nix build without using the daemon
    • the download-speed will get miltiplied by about 10 and it is in a large range around that times 10 value… WHYYYYYYYYYYYYYYYY… probably has smth todo with it starting multiple downloading connections (meaning the --option http-connections 1 is just not working????)
    • you could also use systemd to limit cpu like so: systemd-run -p IOSchedulingPriority=idle -p CPUWeight=idle -p CPUQuota=100% <rest-of-command>

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