Arch Linux

mcloaked

Member

From: Yorkshire, UK

Registered: 2012-02-02

Posts: 1,240

[SOLVED] Wireless speed regression

In recent days I have noticed that my two laptops both have started to have an upper limit on wireless download speed that has gone down more than a factor of ten for downloading files within my local LAN.  Previously both laptops were transferring files at around 125Mbps (i.e. over 15MB/s).  Both laptops use the iwlwifi driver, but have different wireless hardware (one is N-2230 and the other N-7260 but both Intel).   

Typical example this afternoon was a transfer test giving:

$ scp server1:~/Documents/testfile.tar.gz /tmp/
Enter passphrase for key '/home/mike/.ssh/id_ed25519':                                                                  
testfile.tar.gz                                                               100%   45MB   1.1MB/s   00:40

So here the transfer was at 1.1MB/s which is 8.8Mbps - and this has been typical for some days in the past week. I don't know if the regression is due to a kernel driver bug in one of the recent 4.4 kernels or another package.

The iw command gives a transmission rate of 108Mbps:

$ iw dev wlp8s0 link
Connected to xx:xx:xx:xx:xx:xx (on wlp8s0)
        SSID: mdc-guest
        freq: 2422
        RX: 85343793 bytes (160794 packets)
        TX: 4307660 bytes (33143 packets)
        signal: -59 dBm
        tx bitrate: 108.0 MBit/s MCS 5 40MHz

        bss flags:      short-preamble short-slot-time
        dtim period:    1
        beacon int:     100

and the iw dump command shows that the AP should support even higher speeds:

$ iw dev wlp8s0 station dump
Station xx:xx:xx:xx:xx:xx (on wlp8s0)
        inactive time:  3113 ms
        rx bytes:       86769963
        rx packets:     170168
        tx bytes:       4394787
        tx packets:     33568
        tx retries:     5218
        tx failed:      0
        signal:         -57 dBm
        signal avg:     -56 dBm
        tx bitrate:     121.5 MBit/s MCS 6 40MHz
        rx bitrate:     270.0 MBit/s MCS 15 40MHz
        authorized:     yes
        authenticated:  yes
        preamble:       long
        WMM/WME:        yes
        MFP:            no
        TDLS peer:      no

However clearly the achieved throughput is way way lower than the numbers expected from the last two commands. The wireless signal strength is fine, and this is the same using two different wireless routers so it is a change to an arch package that seems to be behind the regression.

Has anyone else seen a huge wireless speed reduction with the iwlwifi module recently?  If so is there a workaround until this is fixed?

Last edited by mcloaked (2016-03-09 18:23:31)

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Mike C

jeremy31

Member

Registered: 2015-11-01

Posts: 149

Re: [SOLVED] Wireless speed regression

Is there any difference if you

sudo modprobe iwlwifi

Then wait a while and

sudo modprobe iwlwifi 11n_disable=8

mcloaked

Member

From: Yorkshire, UK

Registered: 2012-02-02

Posts: 1,240

Re: [SOLVED] Wireless speed regression

Is there any difference if you

sudo modprobe iwlwifi

Then wait a while and

sudo modprobe iwlwifi 11n_disable=8

Doing what you suggested:

# modprobe iwlwifi 11n_disable=8
# iw dev wlp8s0 link
Connected to xx:xx:xx:xx:xx:xx (on wlp8s0)
        SSID: mdc-guest
        freq: 2422
        RX: 897588 bytes (4042 packets)
        TX: 43078 bytes (343 packets)
        signal: -45 dBm
        tx bitrate: 121.5 MBit/s MCS 6 40MHz

        bss flags:      short-preamble short-slot-time
        dtim period:    1
        beacon int:     100

and then doing a test transfer still pegs the achieved rate at 1.1MB/s so this does not resolve the issue.

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Mike C

mcloaked

Member

From: Yorkshire, UK

Registered: 2012-02-02

Posts: 1,240

Re: [SOLVED] Wireless speed regression

I have found the source of the problem - it turned out that one of the routers in my LAN had gone into a strange state - and rebooting that one router has made all of the wireless transfer speeds return to their normal fast state - so this was not caused by any of the arch machines or their settings or the laptops! Apologies for the noise - I wish I had checked the routers well before now! It is a lesson learned that problems with networking can have an origin not where you think the problem lies!   In my case the router involved is a Billion router handling the external WAN, but also connects via gigabit ether to a second wireless router that handles the local wireless connections.  The Billion router had been up for a year or two without any issues - but around the time the problems with wireless speed started there had been a mains power "excursion" and despite the Billion router being protected by UPS with surge protection, it seems that the mains surge had put the router into an abnormal state.  Next time anything like this ever happens I will reboot routers before trying to find the problem with laptop software or settings!

Last edited by mcloaked (2016-03-09 19:07:57)

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Mike C