Linux: How to check whether a process is slowed down by other running processes

Linux: How to check whether a process is slowed down by other running
processes

I have one process running on a RHEL 6.3 machine. Somehow this is taking a
longer processing time than the same process running on another machine.
How is it possible to know why this process is running slow or if any
other parallel running process is slowing down this process?