Open bug in launchpad.net
[ 7578.057461] TCP: wlp1s0: Driver has suspect GRO implementation, TCP performance may be compromised."
This harmless warning should be fixed backporting  to 4.9 series.
I went over iwlwifi commits since then and I couldn't find any issue regarding TCP/GSO. That said, I agree that it seems to be harmless in that setup and that backporting 0b9aefea860063bb39e36bd7fe6c7087fed0ba87 should help on identifying if it's a false-positive or not.
Someone needs to send an email to netdev@ asking for it, though. kernel bugzilla is not how it's done for networking subsystem. More info in ./Documentation/networking/netdev-FAQ.txt . Thanks.
BTW, I had this same warning with vmxnet3 driver with 4.9. I tried a newer kernel and the message didn't appear. I posted my findings here: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=864642#95 - for reference:
It looks like the warning appeared with this first commit:
but was later corrected with this second one:
The first commit was merged in the 4.9 tree, but not the second one (at least not up to 4.9.106), and was only merged in 4.11.
So I would conclude the warning may be harmless, unless you got it on a >= 4.11 kernel. And I also verified I don't get it on such a newer kernel.
I would close this bug, but it may eventually be nice to backport the second commit in 4.9 to avoid the harmless warning.
Searching on the net, there are other reports with the same issue and with various other drivers.
I added in CC: here the net/ipv4 maintainers I found in MAINTAINERS file:
M: "David S. Miller" <firstname.lastname@example.org>
M: Alexey Kuznetsov <email@example.com>
M: Hideaki YOSHIFUJI <firstname.lastname@example.org>
T: git git://git.kernel.org/pub/scm/linux/kernel/git/davem/net.git
I see it Linux 5.5.4 with a OpenVPN(UDP)/tun/VPN tunnel.
TCP: tun0: Driver has suspect GRO implementation, TCP performance may be compromised.
Is this the same bug? Something different?
I see it
TCP: wlan0: Driver has suspect GRO implementation, TCP performance may be compromised.
[ 4.287544] iwlwifi 0000:01:00.0: firmware: direct-loading firmware iwlwifi-8000C-36.ucode
[ 4.289638] iwlwifi 0000:01:00.0: loaded firmware version 36.8fd77bb3.0 op_mode iwlmvm
[ 4.484488] iwlwifi 0000:01:00.0: Detected Intel(R) Dual Band Wireless AC 8260, REV=0x208
[ 4.562788] iwlwifi 0000:01:00.0: base HW address: 28:16:ad:81:b2:8a
[ 4.653536] ieee80211 phy0: Selected rate control algorithm 'iwl-mvm-rs'
root@debian:~# uname -a
Linux debian 5.4.0-4-amd64 #1 SMP Debian 5.4.19-1 (2020-02-13) x86_64 GNU/Linux
In a machine here it happens in a Gigabit Ethernet controller:
[81788.983716] TCP: enp4s0: Driver has suspect GRO implementation, TCP performance may be compromised.
Linux omitted 5.3.0-45-generic #37~18.04.1-Ubuntu SMP Fri Mar 27 15:58:10 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux
This enp4s0 is:
description: Ethernet interface
product: RTL8111/8168/8411 PCI Express Gigabit Ethernet Controller
vendor: Realtek Semiconductor Co., Ltd.
physical id: 0
bus info: pci@0000:04:00.0
logical name: enp4s0
width: 64 bits
capabilities: bus_master cap_list ethernet physical tp 10bt 10bt-fd 100bt 100bt-fd 1000bt-fd autonegotiation
configuration: autonegotiation=on broadcast=yes driver=r8168 driverversion=8.048.00-NAPI duplex=full ip=<omitted> latency=0 link=yes multicast=yes port=twisted pair speed=1Gbit/s
resources: irq:126 ioport:d000(size=256) memory:df104000-df104fff memory:df100000-df103fff
description: RealTek RTL-8168 Gigabit Ethernet driver
ethtool -i enp4s0
( The directory /lib/firmware/rtl_nic/ has the firmware files: rtl8168d-1.fw rtl8168d-2.fw rtl8168e-1.fw rtl8168e-2.fw rtl8168e-3.fw rtl8168f-1.fw rtl8168f-2.fw rtl8168g-1.fw rtl8168g-2.fw rtl8168g-3.fw rtl8168h-1.fw rtl8168h-2.fw )
In a machine here it happens in a RTL8188CE 802.11b/g/n WiFi Adapter (rev 01):
[20965.687617] wlp1s0: associated
[20965.695282] IPv6: ADDRCONF(NETDEV_CHANGE): wlp1s0: link becomes ready
[33544.393882] TCP: wlp1s0: Driver has suspect GRO implementation, TCP performance may be compromised.
$ uname -a
Linux omitted 5.7.0-1.vanilla.1.fc31.x86_64 #1 SMP Mon Jun 1 20:23:36 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux
in old kernels sometimes occur a error:
this msg first time i see in this kernel, is not show in olds...