[PATCH v2 0/2] wifi: ath9k: fix loss of non-aggregate frames

[Tomas Tonhauser]

Non-aggregate frames (stations without an A-MPDU session, e.g.
non-WMM ESP8266 clients) are lost on ath9k in two ways:

 1. The hardware filters them (ATH9K_TXERR_FILT) while the station
    is awake, and mac80211 retries a filtered frame only once.
    Patch 1 sets CLRDMASK on every non-aggregate frame.

 2. Frames that exhaust the hardware retry chain are dropped, as
    there is no software retry for non-aggregate frames. Patch 2
    re-queues failed and filtered frames on tid->retry_q, as the
    aggregate path does.

Toke, I know you were not keen on clearing the filter
unconditionally, so I first tested your suggestion (patch 2) alone.
On a weak link it did much worse than patch 1 alone, and the two
together did best. If you would prefer patch 1 limited, e.g. to
stations that are not sleeping, I can rework it.

Setup: TP-Link EAP225 v3 (QCA9563, 2.4 GHz), OpenWrt 25.12.5,
backports 6.18.26. ESP8266 clients running Tasmota, non-WMM, legacy
rates, modem sleep on (PS_STA toggling constantly).

Weak client (-75 dBm), ping -s 1000 -i 0.05, 500 pings per run:

                     loss         TXERR Filtered   avg RTT
  patch 2 only       52-80%       +544 per run     0.6-1.4 s
  patch 1 only       0-1 pings    0                13 ms

Same client, patches 1+2 plus a test-only module parameter to switch
the software retry at runtime, 12 alternating runs in 11 minutes:

                     lost         tx failed
  retry off (1)      127/3000     130
  retry on (1+2)     1/3000       1

At 1 ping/s, 3 x 25 pings each: 5/75 lost with retry off, 0/75 on.

Other tests with patches 1+2:
 - 500 pings to each of five ESP8266 clients: 0 lost
 - client restarts during ping floods, OTA updates: no issues
 - WMM/HT clients (ESP32, IP camera, tablet): no change
 - 67 h soak: no warnings or resets, MemAvailable flat, ath9k
   queues drain to 0, 3 TXERR Filtered in total

Felix, on the open question from the RFC: on the weak link, filtered
frames appeared together with XRETRY failures, but on the original
good-signal setup they appeared without any. Do you know what sets
the destination mask for an awake station?

Changes since RFC:
 - Patch 1: code unchanged, commit message updated
 - Patch 2: new, alternative 2 from the RFC (Toke)

RFC: https://lore.kernel.org/linux-wireless/20261003192957.761090-1-t.tonhauser@xxxxxxxx/

The driver analysis and write-up were done with help from an LLM.
Tests and measurements were done by me.

Tomas Tonhauser (2):
  wifi: ath9k: clear destination mask for non-aggregate frames
  wifi: ath9k: retry failed non-aggregate frames in software

 drivers/net/wireless/ath/ath9k/xmit.c | 58 +++++++++++++++++++++++++--
 1 file changed, 54 insertions(+), 4 deletions(-)


base-commit: 734bef548a96e8774d6eef5dfa2026c6edc4e80b
-- 
2.34.1