[CentOS] Looking for a method to keep at least 5% CPU

Hi all,
   Sometimes, the working threads occupy 100% CPU, and I just cann't
ssh login with root. my question is: Is there any solution for this
case?
I googled and  found some related links, but not helpful.
http://www.linuxquestions.org/questions/linux-general-1/limit-cpu-usage-for-a-process-269019/




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FIXME if it is wrong.