[Solved] 802.11ax worse than 802.11ac with mt76 driver?

Installing and Using OpenWrt Network and Wireless Configuration
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Your comment made me test again and compare Linux with Windows on the same machine.

I compared the AX to AC 80 MHz performance, with Linux, Windows and on Apple iPadOS, to see if my AX performance issue may be Linux wi-fi driver or firmware related. The iperf3 server now runs on a local Linux machine connected to the E8450 via LAN. The E8450 is now only tested for network performance.

Test environment:

  • Linksys E8450 (UBI), OpenWrt 23.05-SNAPSHOT r23042-3a1cb63336
  • Linux:
    • Debian11, kernel 5.10.0-23-amd64, up to date Intel AX201 firmware-iwlwifi 20210818-1
    • test command: iperf3 -c "iperf3-server" -t 60 -P 4 -i 10 [-R]
  • Windows:
    • Windows 11 22H2, up to date Intel AX201 WiFi driver 22.220.0.4 March 2023
    • Docker Desktop with WSL2 installed
    • test command: docker run -it --rm networkstatic/iperf3 -c "iperf3-server" -t 60 -P 4 -i 10 [-R]
  • Apple:

iperf3 test settings copied from Best practices and tools for measuring wifi performance

OpenWrt mode: AC 80 MHz

Linux client: Connection: 650.0 Mbit/s, 80 MHz, VHT-MCS 7, VHT-NSS 2, Short GI
Upload: [SUM] 0.00-60.00 sec 3.23 GBytes 463 Mbits/sec 135 sender
Download: [SUM] 0.00-60.01 sec 2.10 GBytes 300 Mbits/sec 180 sender

Windows client: connection: 650.0 Mbit/s, 80 MHz, VHT-MCS 7, VHT-NSS 2, Short GI
Upload: [SUM] 0.00-60.00 sec 3.33 GBytes 477 Mbits/sec 1187 sender
Download: [SUM] 0.00-60.01 sec 2.78 GBytes 398 Mbits/sec 45 sender

iPad client: connection: 650.0 Mbit/s, 80 MHz, VHT-MCS 7, VHT-NSS 2, Short GI
Upload: 254 Mbit/s
Download: 387 Mbit/s

OpenWrt mode: AX 80 MHz

Linux client: connection: 720.6 Mbit/s, 80 MHz, HE-MCS 7, HE-NSS 2
Upload: [SUM] 0.00-60.00 sec 1.40 GBytes 201 Mbits/sec 808 sender
Download: [SUM] 0.00-60.01 sec 1.38 GBytes 198 Mbits/sec 717 sender

Windows client: connection: 720.6 Mbit/s, 80 MHz, HE-MCS 7, HE-NSS 2
Upload: [SUM] 0.00-60.00 sec 3.27 GBytes 469 Mbits/sec 1372 sender
Download: [SUM] 0.00-60.01 sec 2.81 GBytes 402 Mbits/sec 0 sender

iPad client: connection: :melting_face:
34.0 Mbit/s, 80 MHz, HE-MCS 0, HE-NSS 1, HE-GI 1
612.5 Mbit/s, 80 MHz, HE-MCS 6, HE-NSS 2, HE-GI 1
Upload: 13 Mbit/s :skull:
Download: 316 Mbit/s

During the 5 minute download testing most of the time the AX iPad Luci RX rate display stays at 34 Mbit/s HE-MCS 0, but some short spikes of higher upload connection rates occur:
408.3 Mbit/s, 80 MHz, HE-MCS 4, HE-NSS 2, HE-GI 1
612.5 Mbit/s, 80 MHz, HE-MCS 6, HE-NSS 2, HE-GI 1

Sometimes during the test the AX iPad RX rate even drops to 24.0 Mbit/s, 20 MHz.

Summary:
Linux: my Debian11 Intel AX201 performance numbers in AX 80 MHz mode are still consistently lower than AC 80 MHz. But that may be a result from the older Linux kernel version or the iwlwifi-firmware from 2021, since the performance in Windows with the up to date Intel driver is on par for AX and AC.

Apple: the very low AX upload performance with my iPad seems to be related to a drop of the RX connection rate to MCS0 NSS1. I think this performance problem could be analyzed more by logging the RX connection from iOS and iPad devices from OpenWrt side during more iperf3 testing.

Is it known why the AX connection E8450 to iPadOS devices drops to HE-MCS0 NSS1 under significant packet load?

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