Marcus Ramos wrote:
>
> Hello,
>
> I am using usleep in an application under RH7 kernel 2.4.2. However,
> when I bring its argument down to 20 miliseconds (20.000 microseconds)
> or less, this seems to be ignored by the function (or the machine's hw
> timer), which behaves as if 20 ms where its lowest acceptable value. How
> can I measure the precision of usleep in my box ? I am currently using
> an Dell GX110 PIII 866 MHz.
>
> Thanks in advance.
> Marcus.
Well, first, your issue is resolution, not precision. Current
resolution on most all timers is 1/HZ. So this should get a min.
nanosleep of 10 ms.
So, could someone explain this line from sys_nanosleep() (
kernel/timer.c):
expire = timespec_to_jiffies(&t) + (t.tv_sec || t.tv_nsec);
It seems to me this should just be:
expire = timespec_to_jiffies(&t)
timespec_to_jiffies(&t) seems to do all the needed resolution round up
and such. Since || is logical, this seems to always add 1, except if
the requested value is 0. The net result is you always get 1 extra
jiffie (unless you ask for zero, in which case you get a timer that will
expire next tick (thru the wonders of add_timer).
George
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This archive was generated by hypermail 2b29 : Mon Apr 23 2001 - 21:00:42 EST