Cpulimit

Cpulimit is a simple program that attempts to limit the cpu usage of a process.
Cpulimit is pre-installed on a lot of distro but if you don't have you can downlaod from here
Syntax : cpulimit OPTIONS... TARGET
Options :
-l : percentage of cpu allowed from 0 to 200 (required)
-z : exit if there is no target process, or if it dies
-i : don't limit children processes
Target :
-e : name of the executable program file or path name
-p : pid of the process (implies -z)

Example:
cpulimit -l 50 -e firefox
Percentage : 50
Program : Firefox
Limit children process : Yes
cpulimit -l 120 -e firefox -i
Percentage: 120
Program : Firefox
Limit children process : No

cpulimit -l 70 -p 1000 -z
Percentage : 70
Pid : 1000

If you have a problem or you need some explanations just write under this post!