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To:     linux-wireless@vger.kernel.org
From:   Qu Wenruo <quwenruo.btrfs@gmx.com>
Subject: Intel 8265 unstable/asymmetric ping response time (only under Linux)
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Date:   Thu, 11 Oct 2018 21:46:58 +0800
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From: Qu Wenruo <quwenruo.btrfs@gmx.com>
To: linux-wireless@vger.kernel.org
Message-ID: <edaca500-8ae2-aef4-1c9d-b754af7e899f@gmx.com>
Subject: Intel 8265 unstable/asymmetric ping response time (only under Linux)

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Hi,

I found one pretty strange behavior for the Intel 8265/8275 wireless
(from ThinkPad X1 carbon)

If I ping *FROM* my router/desktop to the wireless laptop, the response
time is very unstable and slow, like:
------
$ ping -4 thinkpad
PING thinkpad.lan (172.16.0.100) 56(84) bytes of data.
64 bytes from thinkpad.lan (172.16.0.100): icmp_seq=3D1 ttl=3D64 time=3D1=
43 ms
64 bytes from thinkpad.lan (172.16.0.100): icmp_seq=3D2 ttl=3D64 time=3D1=
66 ms
64 bytes from thinkpad.lan (172.16.0.100): icmp_seq=3D3 ttl=3D64 time=3D1=
88 ms
64 bytes from thinkpad.lan (172.16.0.100): icmp_seq=3D4 ttl=3D64 time=3D2=
11 ms
64 bytes from thinkpad.lan (172.16.0.100): icmp_seq=3D5 ttl=3D64 time=3D2=
9.8 ms
64 bytes from thinkpad.lan (172.16.0.100): icmp_seq=3D6 ttl=3D64 time=3D5=
1.7 ms
64 bytes from thinkpad.lan (172.16.0.100): icmp_seq=3D7 ttl=3D64 time=3D7=
2.8 ms
64 bytes from thinkpad.lan (172.16.0.100): icmp_seq=3D8 ttl=3D64 time=3D9=
4.6 ms
64 bytes from thinkpad.lan (172.16.0.100): icmp_seq=3D9 ttl=3D64 time=3D1=
17 ms
64 bytes from thinkpad.lan (172.16.0.100): icmp_seq=3D10 ttl=3D64 time=3D=
140 ms
64 bytes from thinkpad.lan (172.16.0.100): icmp_seq=3D11 ttl=3D64 time=3D=
163 ms
64 bytes from thinkpad.lan (172.16.0.100): icmp_seq=3D12 ttl=3D64 time=3D=
186 ms
64 bytes from thinkpad.lan (172.16.0.100): icmp_seq=3D13 ttl=3D64 time=3D=
207 ms
64 bytes from thinkpad.lan (172.16.0.100): icmp_seq=3D14 ttl=3D64 time=3D=
25.1 ms
64 bytes from thinkpad.lan (172.16.0.100): icmp_seq=3D15 ttl=3D64 time=3D=
47.6 ms
-----

It looks like the response time get increase by 20ms and flipped over
around 200ms.

But when pinging *FROM* the laptop to the router/desktop, it's
completely fine:

------
$ ping openwrt
PING openwrt.lan (172.16.0.1) 56(84) bytes of data.
64 bytes from _gateway (172.16.0.1): icmp_seq=3D1 ttl=3D64 time=3D2.52 ms=

64 bytes from _gateway (172.16.0.1): icmp_seq=3D2 ttl=3D64 time=3D3.59 ms=

64 bytes from _gateway (172.16.0.1): icmp_seq=3D3 ttl=3D64 time=3D2.54 ms=

64 bytes from _gateway (172.16.0.1): icmp_seq=3D4 ttl=3D64 time=3D3.11 ms=

64 bytes from _gateway (172.16.0.1): icmp_seq=3D5 ttl=3D64 time=3D2.93 ms=

64 bytes from _gateway (172.16.0.1): icmp_seq=3D6 ttl=3D64 time=3D2.69 ms=

64 bytes from _gateway (172.16.0.1): icmp_seq=3D7 ttl=3D64 time=3D3.49 ms=

64 bytes from _gateway (172.16.0.1): icmp_seq=3D8 ttl=3D64 time=3D2.58 ms=

64 bytes from _gateway (172.16.0.1): icmp_seq=3D9 ttl=3D64 time=3D2.75 ms=

64 bytes from _gateway (172.16.0.1): icmp_seq=3D10 ttl=3D64 time=3D2.60 m=
s
------

The kernel is 4.18.12-arch1-1-ARCH, so it's pretty new.
The BIOS of the ThinkPad is already updated with fwpud.

BTW, if I boot that thinkpad with Windows, no matter I ping from/to that
laptop, response time is always around 2~3ms.

So is this something wrong with the wireless card or something wrong
with the firmware/powersaving setting of ThinkPad X1 Carbon 6th gen?

Thanks
Qu


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