The 'uptime' command is the quickest way to get an idea. With 4 cores, and your task taking up all the available free capacity, it should be sitting somewhere around 4.0 on all the figures listed after "load averages". This shows you the average utilisation over the last minute, 5 minutes and 15 minutes. The 'top' command will give you an updating list of the processes using most system resources if you're worried another task is using up a lot of the resources (type 'q' to quit it) and if you think you need to mess with how important other tasks are, have a read through the manpage for the 'nice' command.