System process loads 12.5% cpu with no end in sight and not for the first time.

My cpu is i7-2600k@4.2 so 12% is quite a lot actually.
The process does not look suspicious. It has pid4 and NT Kernel & System in description. The amount of threads is over 200.
I can solve it only by restarting in hopes it wont happen again.
What kind of logs do I look for to find out what's this process doing?