mt7925: severe latency + ~21% TX-retries under moderate 5 GHz contention (other radios fine on same AP)

Open
  • Is something wrong?
#1,108 3 comments 1 reaction 0 assignees View on GitHub

Nobody has claimed this yet.

Assessment

Difficulty
5/5
Estimated time
Over a week
Newbie friendliness
35/100
Issue type
Bug
Clarity
Needs clarification
Activity status
Quiet
Tech stack
c, linux
Domain
networking, operating-systems

Research direction

Start by reproducing the contention case with the provided ping, station dump, and survey dump commands, confirming roughly 15–20% OBSS airtime and comparing MT7925 with the other radios. Then trace the mt7925e driver and firmware rate-control or channel-access behavior implicated by the retry measurements. Done means isolating the driver or firmware cause and documenting a validated fix or next diagnostic.

Written by the indexing model from the issue text.

Description

TL;DR — On a ~17% busy 5 GHz channel, MT7925 latency collapses (high TX-retries, 0% loss, stays on-channel), while MT7615 / MT7921 / iPhone on the same AP, channel, and spot are all fine. Same card is flawless on an uncongested channel — the fault is contention-triggered.

⚠️ Not push-button reproducible — it needs real co-channel OBSS airtime (~15–20% here). Instead of a repro script, this is characterized by a controlled same-air comparison + eliminations below.

Environment
  • MT7925 (Filogic 360) [14c3:7925], mt7925e, AMD Ryzen 7 8840HS
  • NixOS, NetworkManager + wpa_supplicant backend
  • Kernel 6.18.38 and 7.1.3 (both affected); firmware WM 20260605
  • Regdomain CN → 5 GHz ch149 / 80 MHz, signal −35…−43 dBm
Controlled comparison — same AP / ch149 / same spot

Channel busy ≈ 17.5% (measured from an adjacent MT7615 iw … survey dump, mostly RX of other BSSes).

client ping → gateway tx-retries
MT7615 (mt76, WiFi5) 3.5 ms, 0 spikes very low
MT7921 / iPhone <20 ms, stable —
MT7925 ~91 ms avg, 54% >15 ms, max ~450 ms ~21% (failed ≈0, loss 0%)

Same MT7925 on a separate low-traffic 5 GHz channel: normal, no spikes.

Ruled out
  • Host/CPU: ping 127.0.0.1 = 0.4 ms during the spikes
  • Roaming/scan: 0 scan/ROC events in iw event over a 54%-spike window
  • Deep-sleep PM: radio awake ~30/35 s, low_power_wakes +0
  • The air: 3 other radios fine on the same channel
To attempt reproduction

Needs ~15–20% OBSS airtime on the operating channel. Rough recipe: a 2nd AP on the same channel + a client pushing steady traffic (iperf/bulk) to reach ~15–20% busy, then from the MT7925 STA:

ping -i 0.02 -c 400 <gateway>                              # latency + spikes
iw dev wlo1 station dump | grep -E "tx packets|tx retries" # retry rate (diff before/after)
iw dev <mt76-on-same-ch> survey dump | grep -A5 'in use'   # confirm channel busy % (2 snapshots)

Suspected: firmware rate-control / channel-access — 21% retries at ~17% busy with −35 dBm is disproportionate; other radios ignore this load.

Dominant language
C
Stars
895
Forks
461
No merged PRs in 30d

Getting set up

This project ships no dev container, Dockerfile or contributing guide, so setting up is up to you: start from its README, and see our first-contribution guide for the general steps.

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

More from openwrt/mt76

All issues in openwrt/mt76

Similar issues

More C issues

Get new issues in your inbox

A short digest of beginner-friendly GitHub issues.