Mysterious, Periodic WiFi Slowdown

zesterer · 2024-08-03 10:02:56

Hello all. I've been observing a strange issue for about a month now. Every 10-20 seconds, I get an absurd slow-down of my Wifi Connection.

Example ping output:

64 bytes from 192.168.1.1: icmp_seq=1 ttl=64 time=6.17 ms
64 bytes from 192.168.1.1: icmp_seq=2 ttl=64 time=2.25 ms
64 bytes from 192.168.1.1: icmp_seq=3 ttl=64 time=5.57 ms
64 bytes from 192.168.1.1: icmp_seq=4 ttl=64 time=5.38 ms
64 bytes from 192.168.1.1: icmp_seq=5 ttl=64 time=2.71 ms
64 bytes from 192.168.1.1: icmp_seq=6 ttl=64 time=2.48 ms
64 bytes from 192.168.1.1: icmp_seq=7 ttl=64 time=2.21 ms
64 bytes from 192.168.1.1: icmp_seq=8 ttl=64 time=2.06 ms
64 bytes from 192.168.1.1: icmp_seq=9 ttl=64 time=2.19 ms
64 bytes from 192.168.1.1: icmp_seq=10 ttl=64 time=2.09 ms
64 bytes from 192.168.1.1: icmp_seq=11 ttl=64 time=3.46 ms
64 bytes from 192.168.1.1: icmp_seq=12 ttl=64 time=1.36 ms
64 bytes from 192.168.1.1: icmp_seq=13 ttl=64 time=10774 ms
64 bytes from 192.168.1.1: icmp_seq=14 ttl=64 time=9754 ms
64 bytes from 192.168.1.1: icmp_seq=15 ttl=64 time=8740 ms
64 bytes from 192.168.1.1: icmp_seq=16 ttl=64 time=7727 ms
64 bytes from 192.168.1.1: icmp_seq=17 ttl=64 time=6719 ms
64 bytes from 192.168.1.1: icmp_seq=18 ttl=64 time=5706 ms
64 bytes from 192.168.1.1: icmp_seq=19 ttl=64 time=576 ms
64 bytes from 192.168.1.1: icmp_seq=20 ttl=64 time=1.82 ms
64 bytes from 192.168.1.1: icmp_seq=21 ttl=64 time=1.89 ms
64 bytes from 192.168.1.1: icmp_seq=22 ttl=64 time=1.78 ms
64 bytes from 192.168.1.1: icmp_seq=23 ttl=64 time=1.98 ms
64 bytes from 192.168.1.1: icmp_seq=24 ttl=64 time=10463 ms
64 bytes from 192.168.1.1: icmp_seq=25 ttl=64 time=9454 ms
64 bytes from 192.168.1.1: icmp_seq=26 ttl=64 time=8443 ms
64 bytes from 192.168.1.1: icmp_seq=27 ttl=64 time=7430 ms
64 bytes from 192.168.1.1: icmp_seq=28 ttl=64 time=6420 ms
64 bytes from 192.168.1.1: icmp_seq=29 ttl=64 time=5403 ms
64 bytes from 192.168.1.1: icmp_seq=30 ttl=64 time=330 ms
64 bytes from 192.168.1.1: icmp_seq=31 ttl=64 time=5.47 ms
64 bytes from 192.168.1.1: icmp_seq=32 ttl=64 time=1.36 ms

Most vexing.

At first, I thought it might be an issue with my router: but after switching router, it still continues (and no other device on the network, Linux or otherwise, shows similar symptoms)

My second theory was that it was a connectivity issue: I live in an old Victorian house with thick stone walls, so I set up Powerline over Ethernet and moved my router such that there was direct line of sight between the router and my PC. Still the same problems (although the minimum ping did drop by about 50%!).

My third theory was that it was a problem with my USB WiFi dongle: my first was a cheapy one from Amazon, so I switched to a TP-Link Archer T2U PLUS, a higher quality dongle. Then I built and installed the following driver for it: https://github.com/morrownr/8821au-20210708. Still, the same periodic slowdowns slowdowns permitted, despite now using an entirely different physical WiFi dongle and an entirely different driver.

So, at this point, I'm out of theories: The only common denominator here *seems* to be the Linux networking stack itself (NetworkManager and so on): I can't think of anything else that I've not tried switching out.

To be clear, there is nothing in the kernel logs (

sudo dmesh

) that looks in the slightest bit suspicious. The driver for the old cheapy WiFi dongle does occasionally crash when trying to set power rate, but even after unloading the relevant kernel module the symptoms are the same as always.

As I say: no other device in the house (including a laptop also running Arch) exhibits the same symptoms: all have consistent ping times within an acceptable, expected range.

When I connect my PC up to a wired connection (either via physical ethernet or via USB tethering of my phone, it itself also using the WiFi) I do not see the symptoms mentioned.

Does anybody have any suggestions about where to go next?

Last edited by zesterer (2024-08-03 10:33:16)

seth · 2024-08-03 14:08:55

Sanity check: Please post the output of

find /etc/systemd -type l -exec test -f {} \; -print | awk -F'/' '{ printf ("%-40s | %s\n", $(NF-0), $(NF-1)) }' | sort -f

If you don't have concurrent network services running ("periodic" kinda yells that) we'll have to look at the system journal to see whether anything suspicious shows up there,

sudo journalctl -b | curl -F 'file=@-' 0x0.st

ieatdirt · 2024-08-03 23:31:43

I had this issue, I had iwd and systemd-networkd both running, which had worked until I updated to Linux 6.10, disabling systemd-networkd and making iwd self-configure it's network fixed everything.

Arch Linux

#1 2024-08-03 10:02:56

Mysterious, Periodic WiFi Slowdown

#2 2024-08-03 14:08:55

Re: Mysterious, Periodic WiFi Slowdown

#3 2024-08-03 23:31:43

Re: Mysterious, Periodic WiFi Slowdown

Board footer