Unexpected Realtime Delay on task 0....

Unfortunately I saw that error again this evening. I went back through the bios, didn't see anything else to turn off. I may try disabling SMI, maybe with the "SMICTRL" approach...

Anything else I can try? Will this run on a RaspberryPI 3B? or 4?

I'm beginning to get really discouraged.

I'm still getting "unexpected realtime delay" or the "error finishing read" and "error queueing read".

I uninstalled the newer networking package, reinstalled network-manager per some instructions. It looks like sometimes the UI is "spinning" trying to establish a connection, while its already connected.

I disabled SMI with SMICTRL.
I used ETHTOOL to turn off IRQ Coalescing (sudo ethtool -C <connection> rx-usecs 0) and it said it was already disabled/nothing to change.

I left a ping running in the background on one test and I saw "network is unreachable" for part of the pings. I tried again and it seems that ping is blocked while GMOCCAPY/LinuxCNC is running?

I ran the Halcmd show param *.tmax thing:

hm2_7i96.0.read.tmax is 1963800 on one run and 1996640 on another. I think that's the problem. for write I saw 5537720 on the slower one, 66740 on the prior test.

I'm about to rip out the computer and chuck it into the yard. I've spent so many days and weeks fighting it. one step forward and two steps back. how does one get Mach going? (half kidding)

Not sure what is going on but, from the start:
-what does uname-a in a terminal say?
-in BIOS, disable everything with hyperthreading, speed step, C states, power saving, virtualization, modem, serial, even sound helps sometimes, built in wifi, secure boot (pc might not boot so new install is needed).
Might have forgotten something ...

I have...

Disabled all there is to disable in the bios.
I've set Isolcpus=1,2,3 (quad core pentium 3700).
C=1 (I think 1, whichever runs full blast all the time)
Disabled sound
Disabled everything I'm not using.
No Wifi
Secure Boot is unchecked in bios
I've disabled SMI via SMICTRL

I per the guy with the goat avatar, PCW, the histogram looks good.

uname -a returns:

Linux printnc 4.19.0-17-rt-amd64 #1 SMP PREEMPT RT Debian 4.19.194-3 (2021-07-18) x86_64 GNU/Linux

i suppose I could find an ethernet USB dongle and disable the onboard Intel ethernet. this is a single board computer (NUC5PPYB I think) so no PCI slots or way to add otherwise.

Strongly considering a raspberry pi

You need the eth port for Mesa, USB dongles do not work for that.
Can you please download the 2.7 version (Wheezy) of LinuxCNC and boot that PC from USB and run latency test for a while, without installing it?
I have a stinking suspicion something is wrong with the hardware, so if it by any chance has two memory modules, yank one out and test, then replace the memory and test again.
Might be the processor is getting to hot and throttling down, so opening the case and having a fan blow over it might help.