I would like to point out one possible omission in the instructions to setup rt-preempt linux image on RPi2/RPi3 (http://www.machinekit.io/docs/getting-started/install-rt-kernel-RPi2/).
By default Raspbian (at least current jessie) disables cpuset cgroup subsystem and therefore you will not be able to mount cpuset filesystem. I would suggest adding cgroup_enable=cpuset to /boot/cmdline.txt
Regards,
F. Moya