nixos-config/machines/shinobu/services/router/tc.nix

# I measured the link capacity with iperf3:
# The download is pretty exactly 7.5 MiB/s ≈ 62.9 Mbit/s
# The upstream is more complicated.
# It initially bursts around 50% higher than the sustained speed
# and then falls down to 569 KiB/s ≈ 4.66 Mbit/s
# However, abound every 2 to 3 seconds, it drops to 380 KiB/s ≈ 3.11 Mbit/s.
# It does so pretty consistently and always at exactly that rate.
# I averaged a longer iperf3 run to around 509 Kbit/s ≈ 4.17 Mbit/s (excluding the initial burst).
{ lib, pkgs, utils, ... }:
let
  cfg = ((pkgs.callPackage ./common.nix { }).tc);

  mkClass =
    { minor
    , rate
    , ceil ? cfg.rate
    , burst ? "15k"
    , qdiscArgs ? [ "fq_codel" ]
    , prio
    }: ''
      tc class add dev ${cfg.interface} parent ${lib.toHexString cfg.major}:1 classid ${lib.toHexString cfg.major}:${lib.toHexString minor} htb rate ${rate} ceil ${ceil} burst ${burst} prio ${toString prio}
      tc qdisc add dev ${cfg.interface} parent ${lib.toHexString cfg.major}:${lib.toHexString minor} handle ${lib.toHexString minor}:1 ${lib.escapeShellArgs qdiscArgs}
    '';
in
{
  systemd.services.traffic-control = {
    after = [ "sys-subsystem-net-devices-${utils.escapeSystemdPath cfg.interface}.device" ];
    bindsTo = [ "sys-subsystem-net-devices-${utils.escapeSystemdPath cfg.interface}.device" ];
    wantedBy = [ "network-online.target" ];

    path = with pkgs; [ iproute2 ];

    script = ''
      set -euo pipefail

      # deleting might fail
      tc qdisc del root dev ${cfg.interface} || true

      tc qdisc add dev ${cfg.interface} root handle ${lib.toHexString cfg.major}:0 htb default 2
      tc class add dev ${cfg.interface} parent ${lib.toHexString cfg.major}:0 classid ${lib.toHexString cfg.major}:1 htb rate ${toString cfg.rate} burst 15k

      ${lib.concatMapStrings mkClass cfg.classes}
    '';

    serviceConfig = {
      Type = "oneshot";
    };
  };
}