passing a reference or passing a value into a subroutine

[chuckdawit]

If I'm passing two strings into a subroutine, is it more efficient to pass a reference or the value? If I'm calling this subroutine a lot (possibly recursively) will I see any performance difference between the two ways of passing the strings into the subroutine? Keep in mind these are strings, they aren't very long, and I'm calling this subroutine often.
Any help on performance would be greatly appreciated.
Thanks,
Chuck