Which LinuxCNC HW for 2026+?

Peter, I am curious if you have tested pinning the NIC IRQ to a non RT core (say second last core). From my research it was better to put the NIC on a different CPU to the RT program which will be running on an isolated core.

There are so many sources of latency to quell on newer hardware and Linux versions

I am hoping that the increasing interest in Linux (thanks to Windows stupidity) doesn't completely bloat Linux into
a slow pig of a system just to satisfy the new masses that don't want to learn anything more then how to turn the
computer on and watch streaming videos.  

Yes I am somewhat guilty of that myself.

Pining the Ethernet IRQ to a non-isolated core  would have the same effect
as not pinning the IRQ at all (especially if irqbalance is disabled as it seems
to be in the standard Debian LinuxCNC distributions)

Thanks, all.

In general, I like the Ethernet solution, especially because it comes with a built-in galvanic isolation.
What I dislike is, that this more or less rules out all notebook solutions, bc I need a network connection.

From what I experienced, but maybe it was all just bad luck, is that all internal WIFI connections do not work,
except for a couple of devices with a PCMCIA wireless card. I did not try every possible combination, but also
USB to Ethernet adapters seem to have a severe impact on latency.

Is my 7i91 too old maybe?
Of course, I set up everything with the help of pncconf and used the default settings wherever possible.

I had latency (network) test running for days without issues; I programmed a Python script to let the A/B tables
rotate for hours flawlessly; but five minutes of probing and error - one real longer milling job and joint error.
I spent hours in front of the HAL scope, just to catch this magic moment. I even had a camera recording it.
Nothing was caught in flagranti.

I now, just for fun, developed a USB to SPI MCU board and started to mod some of the LinuxCNC SPI
code for the 7c81. Not sure yet if isochronous transfer is possible or interrupt transfer would clog everything.
This would be my preferred (notebook) solution.


Which computers are you using for the 7i91? Whenever I browse through all of this here, I only see
10+ years old systems at work (like tommylight’s Thinkpad collection, hehe).
What about a top modern one?

And just to make sure, you all mean PREEMPT-RT, right? Not RTAI. 

When you get a following error, is there a dripped packet?
that is, is hm2_cardname.0.packet-error-total 0?

What are your following error limits?

Can you post a hal/ini file set for a system that exhibits these issues?

I ask because getting following errors and not network timeout errors, that is:
"error finishing read"s is odd and suggests a setup error of some kind

If your PC has a Realtek Ethernet interface, have you installed the DKMS driver?

(the stock Realtek drivers are hopeless latency wise)

If you have in Intel MAC, have you turned off IRQ coalescing?

Have you pinned the Ethernet IRQ to the last processor?

Some systems require disabling  EEE or PCIE power management als

PCW wrote:

Pining the Ethernet IRQ to a non-isolated core  would have the same effect
as not pinning the IRQ at all (especially if irqbalance is disabled as it seems
to be in the standard Debian LinuxCNC distributions)

Thanks, there is quite a few recomendations to keep it on a non isolated core including this one from Intel:
eci.intel.com/docs/3.0.1/development/optimizations.html
Their repo gave me nothing for Trixie.
I wonder if it should be on another isolated core and the servo thread pinned to a different isolated core?