too long hm2_7i97.0.read.tmax or something else?

That does not look bad but the max servo thread time shows the issue
( 1624528  clocks at 1.7 Ghz is ~.95 ms)

It may be that the CPU/BIOS-Setup are simply not capable of the needed
network performance for a 1 KHz servo thread.

A last ditch is to use a newer kernel as the 6.1 kernel in the LinuxCNC distribution
is fairly bad latency wise.

7.0.0-rc1-rt1 #1 SMP PREEMPT_RT 

Is the current one


 

What CPU do you have? How many cpus does it report?
what does echo $(nproc) say?
Its possible you are trying to isolate a nonexistent core

PCW: Thanks for that, I'll consider changing kernel, or maybe trying with another pc.

rodw: processor: Intel(R) Core(TM) i5-8400T CPU @ 1.70GHz, echo $(nproc) prints 5.

thanks, 6 core PC with one isolated = 5 available so that's right. i5 should be fine
What network card? is it Realtek?

I've been researching this today. Here are a few more obscure settings that may help where eno1 is the NOC name from ip a

00:1f.6 Ethernet controller: Intel Corporation Ethernet Connection (7) I219-V (rev 10)
DeviceName: Onboard - Ethernet
Subsystem: Lenovo Ethernet Connection (7) I219-V
Flags: bus master, fast devsel, latency 0, IRQ 120
Memory at b1000000 (32-bit, non-prefetchable) [size=128K]
Capabilities: <access denied>
Kernel driver in use: e1000e
Kernel modules: e1000e

eee was already off, not sure about gro, lro or tso but I will try with them disabled also.

Looking at your first post, its not network related. Note those previous settings do not persist. Running out of ideas. As PCW mentioned ensure the NIC interrupt is pinned to isolated core 5

You mentioned graphics so you probably have an Intel i915 GPU which hangs on my PC. Add these to grub to lock it downi915.enable_dc=0 i915.enable_fbc=0 i915.enable_psr=0