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I have had this old Dell Inspiron 5000 laptop for a while now with no networking issues while running Win2000. Recently, I switched to Linux Mint, which worked pretty well ...
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  1. #1
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    Throttled download speeds


    I have had this old Dell Inspiron 5000 laptop for a while now with no networking issues while running Win2000. Recently, I switched to Linux Mint, which worked pretty well until it developed a strange networking issue.

    It is connected to a DSL-based LAN via 100mbps Ethernet - pretty typical. Usually, the download speeds from most websites tend to be around 340-350mb/s. However, its Ethernet connection seems to be having some strange hiccups. I first noticed problems when I was preparing to make the switch to Lubuntu (to get to a lighter OS for this laptop's meager 384mb of RAM). While I was downloading the .ISO image, the download speed started off fine, then plummeted to around 24mb/s. Of course, this happens sometimes no matter what, and I initially just figured the server was having problems. I opted instead to download the .torrent ISO and try it from there. Transmission, despite having connected to over a dozen peers, wouldn't do above about 34mb/s. On a whim, I killed X and restarted X (sudo service GDM stop/start), and started Transmission again, and lo and behold, the download speed was back up to around 350mb/s. However, after about another 5 minutes of downloading, the speed suddenly cut back to 40mb/s. I restarted X, and it hopped back up to 350mb/s again. I had to play that game over and over to get the Lubuntu ISO to finish downloading at a reasonable speed. But I figured that once I reformatted and installed Lubuntu, the problem would go away. It didn't.

    Lubuntu is having the exact same issue. Every so often, my download speed cuts to around 40mb/s, and the only way to bring it back up again is to restart X. During this cut, the other computer on my LAN still downloads at full speed. Additionally, my modem/router (a single unit) still reports having full 3360kbps download bandwidth. This laptop, however, keeps getting its bandwidth cut, but is always fixed when X is restarted. During the cuts, ping remains exactly the same. If I ping google.com, for example, the ping remains ~50ms. It is just the download speed that gets throttled. Also, when I visit my modem/router's IP address in my browser to check it out, it too is really slow to load (unless of course I restart X, THEN visit my router, at which point the pages load snappily).

    So it seems that it is the laptop's connection with the modem/router is what is getting throttled. However, a freshly restarted X always seems to fix the issue. Note that it has to be a full restart of X. Simply disconnecting and re-connecting the "Auto Eth0" connection via the system tray button does not fix it. I have tried editing the connection and changing the ipv4 method from "Automatic (DHCP)" to "Manual" and inputting all the relevant information (as well as changing the DNS servers from my ISP's to Google's), but it yields the same results and the problem still persists.

    Other than all that, I apologize if I didn't include any other helpful information regarding my problem. I am relatively unfamiliar with networking so I don't know what else to include. Please tell me if there is any other information I can provide, and I thank everyone in advance for help with this. I've been scratching my chin over it for a while now.

  2. #2
    oz
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    Sometimes, intermittent speed issues with the internet can be solved by disabling ipv6, so you might try doing that if you haven't done so already.
    oz

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    I just checked, and "Method" dropbox in the ipv6 page is set to "Ignore" which I assume means disabled. I still don't understand why a quick restart of X fixes the problem temporarily. What could consistently go wrong after a period of time that always starts out right when X is first started? Maybe I should test a long download with X stopped in terminal mode with wget or git or something to see if it ever throttles without X running at all...

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    oz
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    Quote Originally Posted by MuerteBlack View Post
    I just checked, and "Method" dropbox in the ipv6 page is set to "Ignore" which I assume means disabled.
    On a browser level, you can disable ipv6 in Firefox using the about:config option for the browser. For disabling it system-wide, you can google disable ipv6 Linux Mint for some short HowTo articles that should get it disabled. That way, you can be sure it's disabled.
    oz

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    I edited /etc/sysctl.conf and added the lines

    Code:
    #disable ipv6
    net.ipv6.conf.all.disable_ipv6 = 1
    net.ipv6.conf.default.disable_ipv6 = 1
    net.ipv6.conf.lo.disable_ipv6 = 1
    then rebooted and then ran

    Code:
    muerte@thing2:~$ cat /proc/sys/net/ipv6/conf/all/disable_ipv6
    1
    to check that ipv6 was disabled system-wide. I then used Transmission as a benchmark and started downloading the Lubuntu ISO. Like last time, the speed started out at between 350-400kb/s, which is normal for me, then after about 10 minutes, suddenly dropped to about 40kb/s and refused to climb again. I cancelled the torrent, exited Transmission, opened up my browser, and the google homepage was slow to load. I went to the speedtest website (sorry, I can't post links yet) to benchmark my speed, which usually tells me my download speed is about 2.8mbps. But this time, when I checked it, it took forever to even start testing, then finally gave me a result of 0.34mbps as my download speed. I restarted X, and immediately tested again, and the speed was back to 2.8mbps and my torrent was kicking at full speed again. I really don't understand this.


    P.S. Transmission is just the benchmark I'm using to test whether the problem is still occurring after troubleshooting. Realistically, the problem can happen at any time, whether while streaming a video off youtube, downloading a large file normally, or just browsing normally. However, since I have not been able to download this .iso all in one chunk without restarting X several times to keep the speed up, I use it as an indication of where the problem is at. i.e. if I can download the whole thing without having to restart X, I will know that the problem has gone away (which it hasn't yet, it seems).

  7. #6
    Linux Engineer Kloschüssel's Avatar
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    Let's try to isolate the probleM

    Have you tried to bypass your browser by using wget and test download speed?

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    Quote Originally Posted by Kloschüssel View Post
    Let's try to isolate the probleM

    Have you tried to bypass your browser by using wget and test download speed?
    Indeed, I have confirmed that this occurs after around 5-10 minutes of heavy network usage while web browsing, using Transmission, or anything in a virtual terminal like wget, apt-get, aptitude, etc.......... while in the GUI!

    This is the really odd part that I noticed. I just now tested using wget three times, both with X running and without. I used the Ubuntu 10.10 ISO file as a benchmark, as it can be downloaded from a fast, stable mirror. I first ran wget from a terminal in the GUI. The download started out at a respectable 341kb/s, then after about 7 minutes, suddenly plummeted to 40kb/s and stayed there. I then did a "sudo service lxdm stop" to kill X, and from the purely terminal interface, ran wget a second time on the same mirror. The ISO image downloaded in 35 minutes without ever dropping from 341kb/s -- it was completely stable. I started X again via "sudo service lxdm start" and re-ran wget a third time from within the virtual terminal and the speed died again after almost 10 minutes: back down to 40kb/s again. Nothing, including killing the Auto Eth0 connection and then re-enabling it, fixed it other than restarting X, but again, it's temporary.

    So the only time it runs permanently at full speed is when X isn't running. So I guess something in either the X server or elsewhere in the GUI (though remember that this issue has been occurring with both GNOME and LDXE) is messing with the connection somehow. What's also odd is it had this exact problem in Mint, and continues to have it in Lubuntu, so both OS's are experiencing this issue on this laptop with two different desktop environments (GNOME and LDXE).
    Last edited by MuerteBlack; 04-12-2011 at 01:59 AM.

  9. #8
    Linux Engineer Kloschüssel's Avatar
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    Indeed odd and I must confess that your description leaves me astonished.

    First I thought that your isp may be limiting your bandwidth, but he surely wouldn't notice if X is running or not. X couldn't influence that in any way I could think of.


    Well, I gotta try that at home .. would you please post the link to the iso you were downloading just to make sure we're not mixing apples and bananas?

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    The file I was downloading was
    Code:
    mirror.clarkson.edu/ubuntu-releases//maverick/ubuntu-10.10-desktop-i386.iso
    [EDIT] I just had a breakthrough! I compared the list of all running processes with and without X running, paying close attention to anything related to networking. When in the GUI, I saw a process that was not present when X was stopped, which was called "modem-manager". I tested wget again in a terminal, downloading that same file, and waited until the speed was throttled. When I saw the speed suddenly drop down again (this time to 21kb/s! Ouch!!) I killed the modem-manager process which restarted itself, but the download jumped back up to full speed (341kb/s) again.

    So I've isolated the offending process, which is apparently "modem-manager". I'm inexperienced enough with Linux that I'm not familiar with that process. Does anyone know what software package or kernel module it belongs to and/or what it might be doing to slow my speed intermittently and/or how to fix it? It starts out working fine, but it seems to cave in after several minutes of heavy network usage, requiring it to be restarted.
    Last edited by MuerteBlack; 04-13-2011 at 06:57 AM.

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    I apologize for double posting, but it seems my "edit" buttons have disappeared. In any case, things have gotten even more interesting...

    It seems that the modem-manager process is not the direct cause of this issue, but it does seem to contribute in a way that I do not understand.

    I did several things today, producing results that left me scratching my head even more. I was just going to remove the whole "modemmanager" package (assuming it to be the cause of the slowdowns) but found that "lubuntu-desktop" depended on it, so removing it was out of the question. Instead, I took the modem-manager service itself out of commission with

    Code:
    sudo mv /usr/share/dbus-1/system-services/org.freedesktop.ModemManager.service ~
    sudo mv /usr/sbin/modem-manager ~
    and rebooted. After rebooting, I checked to make sure that the service wasn't running anymore (which it wasn't), and then tried the download again. But to my dismay, the speed throttled once again after 10 minutes of downloading. I put the two files back in their proper places and rebooted and ran the download again, waited for the speed to throttle, and then killed the modem-manager service again, which indeed made the speed instantly go back up to full again. So I now know four things about this service:

    1. It only runs when X is running.
    2. When X, thus this service, is not running, my download speeds never get throttled.
    3. If X is running, but this service is disabled, the download speed still throttles after 5-10 minutes.
    4. If both X AND this service are running (the default state), then killing this service fixes the download speeds temporarily (until it slows again after another 5-10 minutes).

    I.... really don't know what to make of those facts. Are there any kind of log files that would be helpful in a situation like this?

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