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networking: cake shaping on WWAN link via NM dispatcher (bufferbloat)

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Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
This commit is contained in:
Sergei Poljanski 2026-10-03 21:35:53 +04:00
commit 573fd9c595
Signed by: asxpi
GPG key ID: 4F8851660FA4121B
1 changed files with 31 additions and 1 deletions
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32
modules/networking.nix
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@ -23,7 +23,7 @@
];
# Kernel modules for WWAN/MBIM modems
boot.kernelModules = [ "cdc_mbim" "qmi_wwan" "cdc_wdm" "mhi" ];
boot.kernelModules = [ "cdc_mbim" "qmi_wwan" "cdc_wdm" "mhi" "sch_cake" "ifb" ];
# MediaTek MT7925 Wi-Fi: disable PCIe ASPM.
# Why: under high throughput (>~50 Mbit/s sustained) the PCIe link enters L1
@ -70,6 +70,36 @@
# profile instead. Re-add a service only if headless autoconnect is needed,
# and if so set the NM profile's autoconnect=no to avoid contention.
# WWAN bufferbloat mitigation (cake shaping on the modem link).
# Why: operator LTE schedulers buffer deeply; loaded latency measured
# 305/449 ms (down/up) at ~51/5 Mbit/s in Gyumri (Viva-MTS, B20+B3+B7 3CA).
# Shaping slightly below measured throughput moves the queue onto this host
# where cake keeps it short — loaded latency dropped to ~70 ms. Applied by a
# NM dispatcher hook so it survives modem reconnects / interface recreation.
# Tune the two rates when the serving cell changes (mmcli / AT+QCAINFO).
networking.networkmanager.dispatcherScripts = [{
type = "basic";
source = pkgs.writeShellScript "wwan-cake" ''
IF="$1"; ACTION="$2"
[[ "$IF" == wwan* ]] || exit 0
TC=${pkgs.iproute2}/bin/tc; IP=${pkgs.iproute2}/bin/ip
IFB="ifb-$IF"; UP=4500kbit; DOWN=45mbit
case "$ACTION" in
up)
$IP link add "$IFB" type ifb 2>/dev/null || true
$IP link set "$IFB" up
$TC qdisc replace dev "$IF" root cake bandwidth $UP besteffort nat ack-filter
$TC qdisc replace dev "$IF" handle ffff: ingress
$TC filter replace dev "$IF" parent ffff: matchall action mirred egress redirect dev "$IFB"
$TC qdisc replace dev "$IFB" root cake bandwidth $DOWN besteffort ingress
;;
down)
$IP link del "$IFB" 2>/dev/null || true
;;
esac
'';
}];
# IVPN service — installed but not auto-started at boot.
# Start manually: `sudo systemctl start ivpn-service`
services.ivpn.enable = true;