QCA6174/Killer 1435 - wifi receive speed halves after several minutes

[Ashley Robjohns]

After normal non-demanding use the receive bitrate drops from approx
550-640 Mbps TCP to 175-250 Mbps TCP after several minutes.  Tested
with iperf3 -c 192.168.0.200 -u -b 300M -t 15  on the local LAN
against another machine connected via ethernet the tests consistently
show degradation of bitrate at around 4-5 minutes.

Link statistics remain stable throughout the connection
signal       -45 to -49 dBm
frequency    5320 MHz
width        80 MHz
RX rate      702–866.7 Mbit/s
TX rate      780–866.7 Mbit/s
VHT NSS      2

Issuing `nmcli connection up "Kite_Net_T"` cycles the wifi and results
in the higher bitrate again for several minutes, with it then dropping
off once more.

This results in d_pdev_resets: +2, but no firmware crash throughout testing

Testing over on LAN with iperf3 -c 192.168.0.200 -u -b 1M -t 300 -R

The first 4m53s were stable, then jitter suddenly increased and still
0% packet loss

...
292–293   996 Kbit/s    0.558 ms
293–294   950 Kbit/s   13.194 ms
294–295   1.03 Mbit/s  14.351 ms
295–296   881 Kbit/s   13.513 ms
296–297   1.05 Mbit/s  13.042 ms
297–298   1.04 Mbit/s  15.800 ms
298–299   1.04 Mbit/s  15.492 ms
299–300   1.01 Mbit/s  13.171 ms

Bitrates will remain like this until the wifi is reset with `nmcli
connection up "Kite_Net_T"` or higher (ie. hardware reset, etc), and
will then again achieve the full 550-640 Mbps before dropping off
again some minutes later.

Dell XPS 9575 2-in-1
Qualcomm Atheros QCA6174, hardware rev 3.2
Rivet/Killer 1435
ath10k_pci
WLAN.RM.4.4.1-00309
Manjaro Testing branch
Kernel 7.2.4-1-Manjaro
AP: Telstra Smart Modem 3
Channel 5320 MHz / 5 GHz
Width: 80 MHz

Any help would be greatly appreciated.


-- 
Ash Robjohns