Very slow realtek 8169 ethernet performance, but only one interface, on ThinkPad T14.

[Qu Wenruo]

Hi,

Not sure if this is a regression or not, but just find out that after upgrading to v5.9 kernel, one of my ethernet port on my ThinkPad T14 (ryzen version) becomes very slow.

Only *2~3* Mbps.

The laptop has two ethernet interfaces, one needs a passive adapter, the other one is a standard RJ45.

The offending one is the one which needs the adapter (eth0).
While the RJ45 one is completely fine.

02:00.0 Ethernet controller: Realtek Semiconductor Co., Ltd. RTL8111/8168/8411 PCI Express Gigabit Ethernet Controller (rev 0e)
05:00.0 Ethernet controller: Realtek Semiconductor Co., Ltd. RTL8111/8168/8411 PCI Express Gigabit Ethernet Controller (rev 15)

The 02:00.0 one is the affected one.

The related dmesgs are:
[   38.110293] r8169 0000:02:00.0: can't disable ASPM; OS doesn't have ASPM control
[   38.126069] libphy: r8169: probed
[   38.126250] r8169 0000:02:00.0 eth0: RTL8168ep/8111ep, 00:2b:67:b3:d9:20, XID 502, IRQ 105
[   38.126252] r8169 0000:02:00.0 eth0: jumbo features [frames: 9194 bytes, tx checksumming: ko]
[   38.126294] r8169 0000:05:00.0: can't disable ASPM; OS doesn't have ASPM control
[   38.126300] r8169 0000:05:00.0: enabling device (0000 -> 0003)
[   38.139355] libphy: r8169: probed
[   38.139523] r8169 0000:05:00.0 eth1: RTL8168h/8111h, 00:2b:67:b3:d9:1f, XID 541, IRQ 107
[   38.139525] r8169 0000:05:00.0 eth1: jumbo features [frames: 9194 bytes, tx checksumming: ko]
[   42.120935] Generic FE-GE Realtek PHY r8169-200:00: attached PHY driver [Generic FE-GE Realtek PHY] (mii_bus:phy_addr=r8169-200:00, irq=IGNORE)
[   42.247646] r8169 0000:02:00.0 eth0: Link is Down
[   42.280799] Generic FE-GE Realtek PHY r8169-500:00: attached PHY driver [Generic FE-GE Realtek PHY] (mii_bus:phy_addr=r8169-500:00, irq=IGNORE)
[   42.477616] r8169 0000:05:00.0 eth1: Link is Down
[   76.479569] r8169 0000:02:00.0 eth0: Link is Up - 1Gbps/Full - flow control rx/tx
[   91.271894] r8169 0000:02:00.0 eth0: Link is Down
[   99.873390] r8169 0000:02:00.0 eth0: Link is Up - 1Gbps/Full - flow control rx/tx
[   99.878938] r8169 0000:02:00.0 eth0: Link is Down
[  102.579290] r8169 0000:02:00.0 eth0: Link is Up - 1Gbps/Full - flow control rx/tx
[  185.086002] r8169 0000:02:00.0 eth0: Link is Down
[  392.884584] r8169 0000:02:00.0 eth0: Link is Up - 1Gbps/Full - flow control rx/tx
[  392.891208] r8169 0000:02:00.0 eth0: Link is Down
[  395.889047] r8169 0000:02:00.0 eth0: Link is Up - 1Gbps/Full - flow control rx/tx
[  406.670738] r8169 0000:02:00.0 eth0: Link is Down

Really nothing strange, even it negotiates to 1Gbps.

But during iperf3, it only goes up to miserable 3Mbps.

Is this some known bug or something special related to the passive adapter?

Since the adapter is passive, and hasn't experience anything wrong for a long time, I really doubt that.

Thanks,
Qu

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