linux-kernel - IWL AC 8260, suspect GRP implementation, broken connectivity

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Message-ID: <20191018063022.6bqunomkyqabgljc@burischnitzel.preining.info>
Date:   Fri, 18 Oct 2019 15:30:22 +0900
From:   Norbert Preining <preining@...ic.at>
To:     linux-wireless@...r.kernel.org, linux-kernel@...r.kernel.org,
        ilw@...ux.intel.com
Subject: IWL AC 8260, suspect GRP implementation, broken connectivity

Dear all,

(please cc)

linux 5.3.N (currently .7), but also older kernels
Debian/sid
Thinkpad X260
iwlwifi 0000:04:00.0: Detected Intel(R) Dual Band Wireless AC 8260, REV=0x208
iwlwifi 0000:04:00.0: loaded firmware version 36.8fd77bb3.0 op_mode iwlmvm

In one particular location I see completely broken connection: dns does
not work (resolve does not work), ping, ssh breaks down, http breaks
down, it really sounds like a really weak connection.

The problem is that:
- the *same* laptop booted into Windows works at high speed connections
- other computers (2 Mac) around here work without problems
- mobile also connects without any problem

There are no RX/TX errors whatsoever. I tried reducing MTU, to no
effect. The only warning I see is
	TCP: wlp4s0: Driver has suspect GRO implementation, TCP performance may be compromised.


wlp4s0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1400
        inet 172.17.1.166  netmask 255.255.0.0  broadcast 172.17.255.255
        inet6 fe80::fddc:f32e:f9cb:fded  prefixlen 64  scopeid 0x20<link>
        ether e4:a7:a0:66:6d:f4  txqueuelen 1000  (Ethernet)
        RX packets 11164  bytes 7459009 (7.1 MiB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 13204  bytes 3062515 (2.9 MiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

I am a bit at loss how to debug this, or better, whether it is possible
to get back normal connectivity?

Thanks a lot for any pointer

Norbert

--
PREINING Norbert                               http://www.preining.info
Accelia Inc. + IFMGA ProGuide + TU Wien + JAIST + TeX Live + Debian Dev
GPG: 0x860CDC13   fp: F7D8 A928 26E3 16A1 9FA0 ACF0 6CAC A448 860C DC13