Buildbot & RTAI ?

You might try in /etc/default/grub
GRUB_CMDLINE_LINUX_DEFAULT="quiet text isolcpus=2,3"

Then run :
$update grub

Reboot and see what happens. It helped on the HP8300 I'm using - even with youtube playing a video it wasn't bad.

,.,.

My understanding - which might be wrong - is that RTAI is married to an old kernel, updating it so it works with current versions is a HUGE task that takes developers away from improving other parts of linuxcnc. At some point, with hardware Ethernet cards, that are quite inexpensive in the bigger picture, should/will replace the old parallel port bit-banging approach. Mesa with a standard RT-kernel is what I am doing. Using Ethernet I/O also gives you a lot of noise immunity for free - should be a much more reliable system.

I used to sell and support a PP EPROM programmer with tight real time timing requirement - once we upgraded to USB - with an embedded processor (similar to using modern Ethernet boards) most support issues disappeared. What the developers did here - tweaking a kernel - training elephants to dance - was extremely impressive, but the effort required to keep RTAI going with newer kernels would consume vast amounts of time.