How to know whether a particular patch is applied to the kernel? Especially RT-Preempt Patch.
In the case of preempt you can just use
uname -v #23 SMP PREEMPT RT Fri Oct 16 11:52:29 CET 2012
The string PREEMPT shows that you use a kernel version with the realtime patch.
Some other patches might also changes the
uname string. So it might also be a help. If this is not the case you can try to look at your
.config. The file could be found in the
/boot directory or (if enabled) by using
cat /proc/config.gz. Maybe there is also a version in
/usr/src/linux (or where you put the kernel sources).
If you found the config file you can grep for specific settings and find out if a patch is used.