When is RT_PREEMPT patch released for linux kernel 4.11, the newest stable Linux Kernel?
I know I can enable CONFIG_PREEMPT in the mainline Linux Kernel but what are the differences between this mainline PREEMPT and the RT_PREEMPT patch? Does the latter do a better job?
Yes, it does better job.
The release date and version is subject to define by working group. Most likely next one will be v4.14 or alike, so called LTS (long term support) version of Linux kernel. Latest available for now is v4.9 or v4.4 -- both are LTS.
More details are provided on the RT Wiki.