Arch Linux

janvr

Member

Registered: 2014-12-23

Posts: 14

[SOLVED] Wireless network half the speed

Hi,
My laptop, a ThinkPad t440s has a slow download speed. I download a 1000mb bin to see my download speed. My laptop has a 6.0mbps (max speed for our internet connection) download speed on ethernet, but on wifi it is only 3mbps.

The weird thing is, I have another t440s that doesn't have that problem (I download the same file from the same server) They both have the same wifi card:Intel Corporation Wireless 7260. (I even tried my 13 year old T61. It also has a 6mbps wifi download speed.)

I tried using a USB wifi dongle, to see if it was my wireless card. I only get 3mbps on my own t440s with the dongle, and on the other t440s i still get 6mbps.

Both the laptops have the same networkmanager version: 1.26.4-1. Any idea what the problem could be?

Thanks, Jan van Rossum

Edit: I just tried on 5GHz instead of 2.4. That didn't have any thresholding, I just got the full 6mbps.

Solution:
Apparantly it was a hardware problem. Last time I opened my laptop to fix the fan I accidentally unplugged one of the wifi cables of the wifi card.

Last edited by janvr (2020-12-04 14:38:11)

seth

Member

From: Won't reply 2 private help req

Registered: 2012-09-03

Posts: 77,685

Re: [SOLVED] Wireless network half the speed

Bluetooth interference?
(Also wifi mouse dongle etc.)

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rallyemax

Member

Registered: 2012-11-09

Posts: 12

Re: [SOLVED] Wireless network half the speed

What version of linux-firmware are you on?

$ pacman -Q linux-firmware

I noticed a significant degradation in my Wifi connection quality (on an Intel AC 8260) when upgrading from 20200916.00a84c5-1 to 20201023.dae4b4c-1. My downlink speeds declined from ~100 Mb/s to 3.5 Mb/s, but that wasn't all -- network activity even at the perceived 3.5 Mb/s caused enough congestion that the Wifi network was barely usable even for other devices.

All the problems went away when I downgraded linux-firmware to version 20200916.00a84c5-1. Relevant to my particular wireless chipset, the file iwlwifi-8000C-36.ucode changed between these two versions, but as far as I can tell these firmware/microcode files are closed source.

I didn't get around to sniffing my wireless network to see what exactly was going on, but clearly the firmware upgrade made my wireless chipset misbehave rather badly. You may well have a different chipset, and possibly even different symptoms, but it's worth checking to see whether the recent firmware update was the culprit. A number of Intel wireless chipset firmwares were modified as part of this update (one commit and another).

For the time being, I'm running completely pinned to the 2020-10-24 state of the repos by pointing pacman's mirrorlist to a snapshot from the Arch Linux Archive. In this case, my /etc/pacman.d/mirrorlist is just:

Server=https://archive.archlinux.org/repos/2020/10/24/$repo/os/$arch

I wish I had a bit more time right now to dig deeper. It's not even easy to determine whether there are any bug reports on this issue because of the various version numbers that may apply. Arch package version 20201023.dae4b4c-1 corresponds to upstream tag 20201022. In my case, the bug is at upstream commit 346057d, which advanced the version of the firmware blob iwlwifi-8000C-36.ucode from 36.79ff3ccf.0 to 36.ad812ee0.0. And yes, I could just keep my system up to date and replace the broken .ucode file, but I really don't like to do that sort of thing (heck, I prefer to keep my entire system pinned than an individual package).

Please report your findings, and if you see an applicable bug report out there, please drop a link to it.

rallyemax

Member

Registered: 2012-11-09

Posts: 12

Re: [SOLVED] Wireless network half the speed

It turns out that in my case, the issue had to do with TCP segmentation offload (TSO). Disabling it like this worked for me, even with the most recent linux-firmware. Re-enabling TSO caused the same issues as before, so the fix wasn't in the newest firmware.

Please give it a shot and mark the post as solved if applicable.

I take it back, disabling TSO isn't working after a couple of reboots, behavior fully reverted. I am now wondering if I inadvertently failed in my attempt to unload my older, pinned linux-firmware version.

Last edited by rallyemax (2020-12-05 18:01:53)