Poor WiFi monitoring performance with RT8821CU

[doragasu]

I am currently developing an application that requires using monitor mode with RT8821CU chipset (rtw88 kernel driver). Previously I was using RaspberryPi OS and everything worked great, but I am moving to Armbian mainly to be able to target more SBCs. The problem is in Armbian, the WiFi monitoring performance is much much worse (at least with the RT8821CU) than with RaspberryPi OS and with my Arch laptop, and I cannot guess why could this be. I have tested on the rpi4b the following:

 

* Build the rtw88 driver with debug and debugfs enabled just in case.

* Test with all the three kernel versions available (edge 6.16, current 6.12, legacy 6.6). None of them achieves decent performance.

* Test the 8821cu driver (**a different driver than the rtw88**): seems to have better perf, but doesnt support the fcsfail feature I need and is quite unstable (for example creating a new interface on the device phy using iw, causes the system to freeze and requires a hard reset, and on some circumstances, calling iwconfig also freezes the system).

* Try all of the above on the community supported OrangePi 3 LTS: same result, I have the same poor WiFi monitoring performance as with the rpi4b

* Cross compile the Raspberry Pi kernel myself (I tried with version 6.6) with rtw88 driver enabled, and manually install it in my rpi4b Armbian SD card (copy the kernel, dtb files and modules, and create appropriate symlinks): I get the same perf as in Raspberry Pi OS!

 

So there must be something with the kernel built with Armbian that is causing this monitoring performance degradation. Unfortunately I am clueless about what could be causing the problem. I have reviewed the kernel configuration, and all options related to the RTW88 driver are the same. But there must be something elsewhere that I cannot find.

 

Any suggestion about what could be the problem or how to debug it? Thanks in advance!

Edited 1 hour ago by doragasu