Julien Michel writes:
 > I would like to measure the time a function spends inside a Caml
 > program, for performance purpose.
 > I need a function with an accuracy of at least 1us.
 > [...]
 > Or generally speaking, does any other function exists to achieve such a
 > measurement (accuracy about 1 us) ?

To do such a measurement, I'm using the Unix.times function, as
follows:

======================================================================
open Unix
  
let utime f x =                                                   
  let u = (times()).tms_utime in                                  
  let y = f x in
  let ut = (times()).tms_utime -. u in
  (y,ut)

let print_utime f x = 
  let (y,ut) = utime f x in
  Printf.printf "user time: %2.2f\n" ut;
  y
======================================================================

Hope this helps,
-- 
Jean-Christophe Filliâtre (http://www.lri.fr/~filliatr)