Arch Linux + MSI B650 Tomahawk WiFi + Realtek RTL8125: network speed degrades over time (900 Mbps → 50 Mbps) until reboot
Arch Linux + MSI B650 Tomahawk WiFi + Realtek RTL8125: network speed degrades over time (900 Mbps → 50 Mbps) until reboot
Hi all,
I’m running Arch Linux and I’m trying to diagnose a networking issue with my onboard Realtek RTL8125 2.5GbE NIC.
Motherboard:
\- MSI MAG B650 Tomahawk WiFi
The problem:
\-After reboot, internet speed is normal (\~900 Mbps)
\-After some hours of uptime, download/upload speed degrades badly (\~50 Mbps or even lower)
\-Reboot immediately restores full speed
\-Latency/ping stays mostly fine
\-No obvious packet loss
\-Happens on Ethernet only
\-This started only recently. I didn’t intentionally change anything major besides normal Arch updates.
Motherboard NIC:
\-RTL8125 2.5GbE Controller
Originally using:
\-r8169
I also tested:
\-r8168-dkms
and even:
\-r8125-dkms
but the issue still happens.
When degraded:
\-Internet becomes extremely slow
\-iperf3 to another LAN machine collapses hard
\-TCP retransmits become very high
\-But ping to router and internet remains stable
Example:
ping 192.168.1.1
Stable:
\~0.3–0.7 ms
0% packet loss
ping 1.1.1.1
Also stable:
\~10–11 ms
0% packet loss
So latency is fine while throughput dies.
iperf3 example during degraded state:
\[ 5\] 0.00-1.00 sec 896 KBytes 7.33 Mbits/sec 61 retr
\[ 5\] 1.00-2.00 sec 512 KBytes 4.19 Mbits/sec 17 retr
...
\[ 5\] 0.00-10.00 sec 6.75 MBytes 5.66 Mbits/sec 146 retr
So retransmits explode under load.
Things I already tested:
Drivers:
\-r8169
\-r8168-dkms
\-r8125-dkms
No real improvement.
Offloads disabled:
sudo ethtool -K enp12s0 gro off gso off tso off
No change.
IRQ balancing:
Installed and enabled:
sudo pacman -S irqbalance
sudo systemctl enable --now irqbalance
NIC interrupt was originally mostly pinned to one CPU core.
After tweaking IRQ affinity + enabling RPS, interrupts spread a little more across CPUs, but issue still happens eventually.
RPS enabled:
for f in /sys/class/net/enp12s0/queues/rx-\*/rps\_cpus; do
echo ffffffff | sudo tee $f
done
Still degrades after some uptime.
EEE already disabled:
EEE status: disabled
qdisc:
Tried:
fq\_codel
pfifo\_fast
No difference
.
Other possibly relevant info:
This machine also runs:
\-Docker
\-k3s
\-multiple bridges/veth interfaces
Interfaces include:
\-docker0
\-cni0
\-flannel.1
\-many veth devices
But even after stopping Docker + k3s, degraded throughput remained.
Things I noticed:
During normal operation:
ethtool enp12s0
shows:
Speed: 1000Mb/s
Duplex: Full
Link detected: yes
No link flaps.
Also:
ip -s link show enp12s0
shows almost no actual errors.
Question:
Has anyone seen:
RTL8125 gradually degrading throughput over uptime on Linux?
r8169/r8168/r8125 all behaving similarly?
interrupt/softirq saturation causing long-term throughput collapse?
Could this still be:
PCIe ASPM?
MSI/MSI-X issue?
AMD B650 chipset quirk?
kernel regression?
firmware/BIOS issue?
Any ideas for deeper debugging would be appreciated because I’m running out of things to test.
Edit:
Additional diagnostic data (during issue / monitoring):
rx_missed: 0
rx_mac_missed: 2243 (and increasing over time)