Excessive network latency when using Realtek R8168/R8111 et al NIC

From: Rod Webster <rod@vmn.com.au>
To: linux-rt-users@vger.kernel.org
Subject: Excessive network latency when using Realtek R8168/R8111 et al NIC
Date: Tue, 18 Apr 2023 13:23:12 +1000	[thread overview]
Message-ID: <CANV1gkc9KvkGNPkEsjXCiV4mUcdrrPcaQ1ueRri9ypjvJbU94g@mail.gmail.com> (raw)

Hi guys,
I hope this is the right place to report an issue

We are linuxcnc users and as such we are long term users of PREEMPT_RT
on x86 (and some other platforms)

A number of PC's in use by our members have recently been experiencing
excessive Real Time network latency since the 5.10 kernel and above.

We are excited to see this seems to have been mostly resolved with the
6.3 kernel compiled from patched kernel.org source.

But we are also experiencing excessive Real time network latency on
some NIC hardware, mostly with  Realtek NIC's in this list.

https://www.realtek.com/en/component/zoo/category/network-interface-controllers-10-100-1000m-gigabit-ethernet-pci-express-software
Many modern industrial PC's are using Realtek NIC drivers that cannot
be changed out so this is a problem for us.

It's our understanding that the R8169 kernel driver module should
provide support for this hardware. It does indeed do this but real
time network latency is unacceptable. Debian offers  a R8168-dkms
driver.  I understand it is being deprecated in favor of the R8169
kernel module driver.

Installing the R8168-dkms driver on the 6.3 kernel improves RT network
latency/jitter by 400% over the R8169 driver.

We are users not kernel developers. How can we escalate this issue so
acceptable RT performance is restored?

end
-Regards
-Rod Webster