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

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Message-ID: <trinity-92c3826f-c2c8-40af-8339-bc6d0d3ffea4-1678213958520@3c-app-gmx-bs16>
Date:   Tue, 7 Mar 2023 19:32:38 +0100
From:   Frank Wunderlich <frank-w@...lic-files.de>
To:     Felix Fietkau <nbd@....name>, Mark Lee <Mark-MC.Lee@...iatek.com>,
        Sean Wang <sean.wang@...iatek.com>,
        Daniel Golle <daniel@...rotopia.org>
Cc:     Lorenzo Bianconi <lorenzo@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        John Crispin <john@...ozen.org>,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>, netdev@...r.kernel.org,
        linux-mediatek@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org
Subject: [BUG] MTK SoC Ethernet throughput TX only ~620Mbit/s since 6.2-rc1

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.

example output before revert on mt7623/bpi.r2:

root@...-r2:~# iperf3 -c 192.168.0.21
Connecting to host 192.168.0.21, port 5201
[ 5] local 192.168.0.11 port 48882 connected to 192.168.0.21 port 5201
[ ID] Interval Transfer Bitrate Retr Cwnd
[ 5] 0.00-1.00 sec 75.3 MBytes 632 Mbits/sec 0 396 KBytes
[ 5] 1.00-2.00 sec 74.3 MBytes 623 Mbits/sec 0 396 KBytes
[ 5] 2.00-3.00 sec 74.6 MBytes 625 Mbits/sec 0 396 KBytes
[ 5] 3.00-4.00 sec 73.9 MBytes 620 Mbits/sec 0 396 KBytes
[ 5] 4.00-5.00 sec 74.6 MBytes 626 Mbits/sec 0 396 KBytes
[ 5] 5.00-6.00 sec 74.4 MBytes 624 Mbits/sec 0 396 KBytes
[ 5] 6.00-7.00 sec 74.4 MBytes 624 Mbits/sec 0 396 KBytes
[ 5] 7.00-8.00 sec 74.4 MBytes 624 Mbits/sec 0 396 KBytes
[ 5] 8.00-9.00 sec 73.9 MBytes 620 Mbits/sec 0 396 KBytes
[ 5] 9.00-10.00 sec 74.6 MBytes 626 Mbits/sec 0 396 KBytes
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval Transfer Bitrate Retr
[ 5] 0.00-10.00 sec 745 MBytes 625 Mbits/sec 0 sender
[ 5] 0.00-10.05 sec 744 MBytes 621 Mbits/sec receiver

iperf Done.
root@...-r2:~# ethtool -S eth0 | grep -v ': 0'
NIC statistics:
tx_bytes: 819999267
tx_packets: 538815
rx_bytes: 18338089
rx_packets: 261984
p06_TxUnicast: 261974
p06_TxMulticast: 10
p06_TxPktSz65To127: 261983
p06_TxPktSz256To511: 1
p06_TxBytes: 19386025
p06_RxFiltering: 13
p06_RxUnicast: 538783
p06_RxMulticast: 31
p06_RxBroadcast: 1
p06_RxPktSz64: 3
p06_RxPktSz65To127: 47
p06_RxPktSz128To255: 2
p06_RxPktSz256To511: 1
p06_RxPktSz512To1023: 2
p06_RxPktSz1024ToMax: 538760
p06_RxBytes: 819999267

Hope i've forgot no information for now :)

regards Frank