To patch the kernel we can simple follow one of the tutorials online (see ).
But for the kernel version 4.9.88 we can not find a matching rt patch. But a older one is working nice for this issue, see .
This will patch the kernel ready for compilation, but it is recommended to adjust the realtime priorities, see  for this. Otherwise a realtime application can sporadically block your system.
I also attached both patches for every one how wants to use it.