Fritzbox 4040 upgraded to 21.02.2, one client has extremely poor 2.4GHz wireless performance

Fritzbox 4040, client is a BMAX Y13 running Debian / testing, with kernel 5.16.0-3 / -4 and wifi is Intel Wireless-AC 9461.

A LAN transfer with, say, scp would easily top 5MB/s with 21.02.1 whereas now it either stalls or crawls around at a measly 50kB/s even though the wifi link speed is nominal. With older point release it would not matter which band was used: the VDSL2 WAN link (70/20) could be saturated either way; with the current version, on 2.4GHz the performance is abysmal and on 5GHz it is mostly fine.

What could be the issue here?

fwiw, poor performance is known problem with 2.4 GHz on EA6350 v3 which uses same SoC.

Check out the optimized build this thread. 4040 is supported

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Is it version 19.07 or 21.02 ? You kinda mixed both in the thread title :wink:

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Fixed title and text, nice catch

I'll have a look... if I can keep devices on the higher band I'm fine, then.

Without resorting to such drastic changes as another build or a version rollback, is there anything else I can try? Change of firmware, perhaps? I'm baffled that such a degradation occured in a point release.

For the moment, I have set a band preference on the two laptops and that should cover it.

I would try the "ath10k + ath10k-firmware-qca4019" driver package instead of "ath10k-ct + ath10k-firmware-qca4019-ct" even if it shouldn't have changed from 21.02.1 -> 21.02.2.
I had troubles when using ath10k-ct driver which didn't occur with the vanilla ath10k driver.

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Make sure that WMM is enabled.

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WMM is enabled on all SSIDs, I'll try the firmware change when I have a spare moment, thanks.

I used the firmware builder (online, via auc) so the firmware is in the /rom tree. Granted, I can install the new driver and new firmware but how do I switch to that?

If you are using a release version, just remove ath10k-firmware-qca4019-ct and kmod-ath10k-ct and install kmod-ath10k-firmware-qca4019 and kmod-ath10k via shell or web interface.

I'm not sure whether an image generated via AUC qualifies as "release" version but I've done that, restarted the radio with "wifi" and forced the laptop on the 2.4GHz band: the performance is still less than on the high band but not at all terrible, so I think it could be working. Is there anything in logread that will tell me exactly which firmware has been loaded?