Re: nanosleep

["H. Peter Anvin" <hpa@zytor.com>]

Followup to:  <20020410044243.2916.qmail@fastermail.com>
By author:    "mark manning" <mark.manning@fastermail.com>
In newsgroup: linux.dev.kernel
>
> thanx - how much of a difference should i expect - i know the
> syscall is asking for at least the required ammount but that the
> task switcher might not give me control back for a while after the
> requested delay but i was expecting to be a little closer to what i
> had asked for - this isnt critical of corse but i would like to know
> what to expect.
> 

Read the man page:

BUGS
       The current implementation of nanosleep is  based  on  the
       normal  kernel  timer mechanism, which has a resolution of
       1/HZ s (i.e, 10 ms on Linux/i386 and 1 ms on Linux/Alpha).
       Therefore, nanosleep pauses always for at least the speci­
       fied time, however it can take up to  10  ms  longer  than
       specified  until  the  process becomes runnable again. For
       the same reason, the value returned in case of a delivered
       signal  in *rem is usually rounded to the next larger mul­
       tiple of 1/HZ s.

       As some applications  require  much  more  precise  pauses
       (e.g.,  in  order to control some time-critical hardware),
       nanosleep is also capable of short high-precision  pauses.
       If  the process is scheduled under a real-time policy like
       SCHED_FIFO or SCHED_RR, then pauses of up to 2 ms will  be
       performed as busy waits with microsecond precision.

	-hpa
-- 
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