usleep, rtl_delay and clock_nanosleep performance

[Raul <raulrtl@yahoo.co.uk>]

Hi all
I need a 25 usec delay within a rt thread. Somewhere I
read that rtl_delay() should not be used (I take it
because it is blocking), instead usleep() or
clock_nanosleep() are preferable. However when I
measured the actual delay of these functions I found
that clock_nanosleep and usleep make a wait of nearly
50 usec (somthing to do with the scheduling?) whereas
rtl_delay() is more precise, with a wait of 27 usec. 
Is the use of a non-blocking function with a poorer
precission a compromise? Is rtl_delay not advisable to
use under any circunstances, even if I guarantee that
the rt thread period will be larger than 25 usec?
thanks again
Raul

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