Arch Linux

tmoore

Member

Registered: 2012-06-03

Posts: 5

systemd-239.0-2 reduces download speeds

So I've been fighting with this issue a few days.. Running archlinux on x86_64 with latest patches as of yesterday.  I happened to notice that my download speeds that were normally 300Mbit down were suddenly at 50Mbit down.  Strange thing was that inside a docker container on the same machine, the speeds were 300Mbit down.  So I go and test on my Windows PC, 300Mbit down.  I then login to another separate archlinux server and it's 50Mbit down as well.   

So I start the google search parade. trying things, tcp windows, router checks, etc.  Finally I make a bootable archiso and start that up.  Lo and behold, 300Mbit down on the machine that was 50Mbit.

So I pacstrap my machine again, boot it up, and it's back to 50Mbit/s

I finally wipe the drive again, rebuild my harddrive OS from the archlinux usb iso files directly https://wiki.archlinux.org/index.php/Ar … net_access, and don't upgrade any packages.

Reboot, lo and behold, 300Mbit down again.. So I start upgrading one package at a time and rebooting, everything is fine until I hit "systemd"

upgraded systemd (238.133-4 -> 239.0-2)

As soon as that was done, even before I rebooted, my speedtest showed 50Mbit/s again. 

So I downloaded 238.133-4 again from archive, installed it, and tested, still 50Mbit/s.. Then I rebooted, back to 300Mbit/s

So .. something in 239.0-2 is screwing with the network stack, and I'm not sure how to fix it as my box is a clean pristine install (just base).  I'm not even sure how to debug.  I've read the release notes, but nothing pops out at me.

Anyone else see/have this issue?

ewaller

Administrator

From: Pasadena, CA

Registered: 2009-07-13

Posts: 19,791

Re: systemd-239.0-2 reduces download speeds

It is unfortunate you failed to even tell us if you are using wired or wireless.
I am sure you looked at the output of ip and iw to see what the capabilities of the network were.

My hunch is that you are using wireless and are associating with a b/g/n 2.5GHz link instead of an n/ac 5 GHz link.  But, I could be wrong.

You might also consider sharing your NIC's chip set, what you are using to control your network, what router/network to which you are attaching, etc....

Edit:  PS; it probably has squat to do with systemd

Last edited by ewaller (2018-07-17 02:17:45)

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tmoore

Member

Registered: 2012-06-03

Posts: 5

Re: systemd-239.0-2 reduces download speeds

Ah yes, I missed very important points..

WIRED

04:00.0 Ethernet controller: Realtek Semiconductor Co., Ltd. RTL8111/8168/8411 PCI Express Gigabit Ethernet Controller (rev 01)

cat /etc/systemd/network/enp5s0.network
[Match]
Name=enp4s0

[Network]
Address=192.168.1.3/24
Gateway=192.168.1.1
DNS=208.67.222.222
DNS=208.67.220.220

Chipset is a LGA775 and the other machine with the same issue is a HP Mini, (2 years old and wired as well).

Very simple x86 PC.

The fact that downgrading systemd fixed the issue points to that specific package.  I can reproduce over and over.

Last edited by tmoore (2018-07-17 04:02:01)

ewaller

Administrator

From: Pasadena, CA

Registered: 2009-07-13

Posts: 19,791

Re: systemd-239.0-2 reduces download speeds

The fact that downgrading systemd fixed the issue points to that specific package.  I can reproduce over and over.

Fair enough.

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Nothing is too wonderful to be true, if it be consistent with the laws of nature -- Michael Faraday
Sometimes it is the people no one can imagine anything of who do the things no one can imagine. -- Alan Turing
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How to Ask Questions the Smart Way

loqs

Member

Registered: 2014-03-06

Posts: 17,372

Re: systemd-239.0-2 reduces download speeds

https://github.com/systemd/systemd/blob/master/NEWS

 * The "net.ipv4.tcp_ecn" sysctl will now be turned on by default.

If it is not that I would suggest bisecting between systemd 238 and 239 to find the cause.
Edit:
238 and 239 not 239 and 239

Last edited by loqs (2018-07-17 09:45:29)

tmoore

Member

Registered: 2012-06-03

Posts: 5

Re: systemd-239.0-2 reduces download speeds

https://github.com/systemd/systemd/blob/master/NEWS

 * The "net.ipv4.tcp_ecn" sysctl will now be turned on by default.

If it is not that I would suggest bisecting between systemd 238 and 239 to find the cause.
Edit:
238 and 239 not 239 and 239

Setting it to "0" fixed the issue!  Wow.. you really nailed it.

So apparently the default setting with 238 was "0", and with 239 it is "1".  Setting it back to 0 make it instantly work correctly.

I wonder how many people this affects?

Last edited by tmoore (2018-07-17 14:04:09)

loqs

Member

Registered: 2014-03-06

Posts: 17,372

Re: systemd-239.0-2 reduces download speeds

Something breaking ECN and fallback detection failing or ECN is working but being overly aggressive in throttling.