Single Status Update
I've got a PFsense-router as my main, Internet-facing router, which is then followed by a big switch and to this switch are all of my devices connected, including one Zyxel WiFi-router upstairs and one Linksys WRT1900ACS WiFi-router downstairs. Both of these WiFi-routers are running OpenWRT.
Now, I've had this feeling that something's off with the Linksys and e.g. GeForce Now and Project xCloud both complain about high latency when connected to it, but not when connected to the Zyxel. Speedtest doesn't show any issues and I am getting ~500Mbps out of the Linksys, so I haven't understood the problem. Well, just a few days ago I happened to be using Parsec to do stuff and I came to realize that Parsec does show network-latency and...when connected to the Zyxel, it's showing about 0.9ms whereas with the Linksys it's showing 30-60 ms network-latency! That's fricking terrible! No wonder it's always felt so off!
Took me a good while and hours of messing around to figure what was wrong and how to fix it. Nothing seemed to work, not even full reset, until I found a thread on Github where someone was complaining about similar issues. Apparently, there's a feature called A-MSDU, that's supposed to work fine and is part of the 802.11ac - specs, but it's not working right with the Marvell 88W8864 WiFi-chipset using mwlwifi - driver -- after disabling AMSDU, I finally got the expected 0.9ms latency over WiFi on the Linksys as well!
If anyone reading this ever stumbles upon the same issue, the fix in my case was to add the two following lines to a startup-script:
echo 0 > /sys/kernel/debug/ieee80211/phy0/mwlwifi/tx_amsdu
echo 0 > /sys/kernel/debug/ieee80211/phy1/mwlwifi/tx_amsdu
@2FAEh, Marvell's stuff is generally apparently rather poorly supported. It seems the company just doesn't much like open-source. Ath10k for Atheros-chipsets, on the other hand, seems to work just fabulously.
If/when I some day replace the router, I'll have to pay more attention to avoid both Broadcom and Marvell.