See Re: CPU usage Windows OP, but realise that if you thinking of using these instantaneous values for anything other than display purposes, by the time you get the numbers in Perl, they are out-of-date and so wildly inaccurate. This will be the case regardless of which OS and how you get the numbers.

If you are thinking of basing any processing decisions upon them, you are going to be very disappointed. It'd be a bit like trying to play the stock market based upon those 20-minute delayed 'free' price feeds. By the time you get the information, the real situation will have changed, up or down and probably several times up and down.

Whatever action you take as a 'reaction' to the numbers you obtain will essentially be random.