Tracking down stuttering (deb-12, LinuxCNC-2.9)

I'm converting a Langmuir MR-1 gantry mill to LinuxCNC.  I originally started with the current 2.8-series boot image, but decided to move to 2.9 to take advantage of python3.  My machine has debian12, LinuxCNC 2.9.  I'm currently using pyqtvcp, but had the same problem with axis.  My hardware is interfaced through a Mesa 7i96S.  My latency histogram is decent but not awesome with the servo-thread showing min(us) of -42.6 and max(us) of 42.3 while the machine is under heavy load.  I've set isolcpus=2,3 (my machine uses a 4-thread/2-core Intel i5).

I am using the built-in wifi and ethernet, but have turned of all other system devices in the bios (touch screen, sound, etc).

When I'm jogging I'm getting inconsistent speeds and I can also see the current velocity number in the UI dropping when I hear the stepper stutter.  A theory is that the 7i96S is finishing a command and that the next one hasn't been enqueued yet, so that is when I'm hearing the stutter.  I can also hear the same issues on long rapid commands.

I didn't have these issues when using the same PC, Mesa, and machine on LinuxCNC 2.8.x.  I know that I'm on the bleeding edge using Deb-12 and LinuxCNC 2.9, though both are close to release.

What can I look for to track these issues down?

Only while jogging or even when running programs?

Since it is happening on long programmed rapids (G0 across the full diagonal of the machine) I expect that it will also happen when running programs.

I haven't run a real program on it since moving to Debian 12, I'm still trying to dial it in and get my probing routines working.

You have to check that as the stuttering is usually a keyboard issue that shows up only when jogging.

Since it happens on long G0 commands typed into the MDI I don't think it is a keyboard issue.

awetmore wrote:

Since it happens on long G0 commands typed into the MDI I don't think it is a keyboard issue.

Yes, that is correct.
Things to check:
Power supply, if there is a LED see if it changes intensity while machine is doing a rapid
Drives, check current settings, to much current skips steps same as to little current, but makes more noise
In the ini file, set steplen and stepspace to at least 5000 while testing.
Also ini file, dirsetup and dirhold to 20000