From: Roy Turner <umcs.maine.edu at rmt>
   
      o capturing *trace-output*, using the "time" macro to gather times, then
        taking the returned string apart to get the time; the problem with this
        is that you can't trace anything without modifying the code to not use
        the time function, or to conditionally use the time function.

Why not this?

    (defmacro my-time (form)
      (let ((oto (gensym)))
	`(let ((,oto *trace-output*))
	   (process-time-string		; However you parse the time output.
	    (with-output-to-string (*trace-output*)
	      (time (let ((*trace-output* ,oto)) ,form)))))))

This doesn't return the results of evaluating the timed form, but you
could easily fix that if you want transparency.

        Since the
        code is pretty stable, this isn't too bad, but they solution is hideously
        inelegant -- there are obviously functions time is using to gather the
        times, so using the intermediate string is dumb.
      o using the undocumented function excl::get-internal-run-times in
        conjunction with the standard get-internal-run-time to get the GC time:

The four returned values are in milliseconds:
  user non-gc time
  system non-gc time
  user gc time
  system gc time

If I were you I would carefully verify the reasonableness of the
returned values on whatever platform you are using, and don't depend
on this function working the same way in any future version or
different platform.