[BUG] MTK SoC Ethernet throughput TX only ~620Mbit/s since 6.2-rc1

[Felix Fietkau]

On 07.03.23 19:32, Frank Wunderlich wrote:
> Hi,
> 
> i've noticed that beginning on 6.2-rc1 the throughput on my Bananapi-R2 and Bananapi-R3 goes from 940Mbit/s down do 620Mbit/s since 6.2-rc1.
> Only TX (from SBC PoV) is affected, RX is still 940Mbit/s.
> 
> i bisected this to this commit:
> 
> f63959c7eec3151c30a2ee0d351827b62e742dcb ("net: ethernet: mtk_eth_soc: implement multi-queue support for per-port queues")
> 
> Daniel reported me that this is known so far and they need assistance from MTK and i should report it officially.
> 
> As far as i understand it the commit should fix problems with clients using non-GBE speeds (10/100 Mbit/s) on the Gbit-capable dsa
> interfaces (mt753x connected) behind the mac, but now the Gigabit speed is no more reached.
> I see no CRC/dropped packets, retransmitts or similar.
> 
> after reverting the commit above i get 940Mbit like in rx direction, but this will introduce the problems mentioned above so this not a complete fix.
I don't have a BPI-R2, but I tested on BPI-R3 and can't reproduce this 
issue. Do you see it on all ports, or only on specific ones?

- Felix