Slow download speed kubuntu 23.04 starting from kernel 6.2.0-25

[Giovanni Panozzo]

After upgrading kernel to linux-image-6.2.0-25-generic (or -26), I experience slow download speed (20-30Mbps instead of the expected 500Mbps-1Gbps). This happens with firefox, chrome, chromium and wget. Upload speeds are ok.

Downloads in LAN seems not to be affected. Only from the Internet (i.e.: speedtest.net with firefox/chrome/chromium or some big ISO files downloads).

When booting with older kernel, i.e. 6.2.0-24, the problem disappear.

My network card is a Realtek, see attached lspci output, and is using r8169 module.
PC is a Dell Optiplex 3080

/proc/version_signature: Ubuntu 6.2.0-26.26-generic 6.2.13
lspci output is attached

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Johannes Hessellund (osos)]

I can confirm this bug. Using Linux Mint here. Noticed decrease after upgrading to latest. Reverting to kernel 5.19.0-43-generic solved it.

Download speed with kernel 5.19.0-43 = 980mbit/s
Download speed with kernel 6.2.0-25 = 50-70mbit/s

Upload speed both = 980mbit/s

lspci:
Ethernet controller: Realtek Semiconductor Co., Ltd. RTL8111/8168/8411 PCI Express Gigabit Ethernet Controller (rev 15)

[Mike Ferreira (mafoelffen)]

Re: This bug report: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/2031240
Seems to be a duplicate of this one, but since this was reported earlier, the other should probable be marked as the duplicate.

Same thing going on between both.

The User says his system is using the 'r8169' module. One of the default in the 6.2 kernel Change Log for that module dealt directly with changing the default from highest speed to something "conservative" to avoid some problems some people were having with ASPM:

RE: https://cdn.kernel.org/pub/linux/kernel/v6.x/ChangeLog-6.2

Quote:
"commit 32163491c0c205ffb1596baf9c308dee5338ae94
Merge: 65e6af6cebefb 42f66a44d8371
Author: David S. Miller <email address hidden>
Date: Sat Dec 3 21:49:23 2022 +0000

    Merge branch 'r8169-irq-coalesce'

    Heiner Kallweit says:

    ====================
    net: add and use netdev_sw_irq_coalesce_default_on()

    There are reports about r8169 not reaching full line speed on certain
    systems (e.g. SBC's) with a 2.5Gbps link.
    There was a time when hardware interrupt coalescing was enabled per
    default, but this was changed due to ASPM-related issues on few systems.

    Meanwhile we have sysfs attributes for controlling kind of
    "software interrupt coalescing" on the GRO level. However most distros
    and users don't know about it. So lets set a conservative default for
    both involved parameters. Users can still override the defaults via
    sysfs. Don't enable these settings on the fast ethernet chip versions,
    they are slow enough.

    Even with these conservative setting interrupt load on my 1Gbps test
    system reduced significantly.

    Follow Jakub's suggestion and put this functionality into net core
    so that other MAC drivers can reuse it.
    ====================

    Signed-off-by: David S. Miller <email address hidden>"

I'm thinking that this change may have happened and may occur because of that default change.

[Johannes Hessellund (osos)]

installing r8168-dkms seems to better the result, but not completely solve it.

Suggested here: https://askubuntu.com/q/1488178

Afterwards download is 920 mbit and upload 400 mbit, should be 980/980 mbit.