l2-max wrote: I do not think my tweaks will help you much as you and I running different Debian releases.
Initially, latency test on this mother board shown 16uS with official RTAI 2.7.14 ISO image. Then I switched to 2.8 master branch. Latency remain exactly the same as with official release despite kernel changed to preempt-rt. If you cannot reach such latency with clean 2.7.14 RTAI on the motherboard then I am not sure my BIOS setup will help you much.
Sorry, I do not have LinuxCNC machine by hand thus, what I recall, I disabled "INTEL speed step" (-3uS) to run processor at constant speed and may be, not sure disabled virtualization (not sure it had some impact on latency). I also isolated CPU on 2 cores only (that tweak helped a lot -8uS) and latency dropped down to 5uS.
That is it, from what I remember had noticeable impact on latency. Try booting from 2.7.14 RTAI flash drive and run latency test to see if it will be different from what you have now.
I briefly installed RTIA at first and I had very low latency numbers as well. Many around 16uS like you.
But I have an ethernet Mesa 7i92 card so I had to switch to PREEMP. With the official image I was getting about 50-70uS, but had ramdom spikes up to several seconds. Tried lots of tweaks that lowered latency a bit but didn't get rid of the spikes.
Maybe it would have helped if SMICTRL had worked at all for me.
Tried Mint and Lubuntu as well, but it didn't help.
Now I'm back on Debian 9, latest version, with pre-compiled PREEMT from rep. I don't get those 2-3s spikes any more. Now they only reach maybe 120uS.
But since I'm using a Mesa card I guess my numbers are ok.
