2007/8/17, Michal Schmidt <[EMAIL PROTECTED]>:
> GolovaSteek skrev:
> > Hello!
> > I need use sleep with accurat timing.
> > I use 2.6.21 with rt-prempt patch.
> > with enabled rt_preempt, dyn_ticks, and local_apic
> > But
> >
> > req.tv_nsec = 30;
> > req.tv_sec = 0;
> > nanosleep(,NULL)
> >
> > make pause around 310-330 microseconds.
>
> How do you measure this?
> If you want to have something done every 300 microseconds, you must not
> sleep for 300 microseconds in each iteration, because you'd accumulate
> errors. Use a periodic timer or use the current time to compute how long
> to sleep in each iteration. Take a look how cyclictest does it.
no. I just want my programm go to sleep sometimes and wake up in correct time.
> > I tried to understend how work nanosleep(), but it not depends from
> > jiffies and from smp_apic_timer_interrupt.
> >
> > When can accuracy be lost?
> > And how are process waked up?
> >
> >
> > GolovaSteek
>
> Don't forget the process will always have non-zero wakeup latency. It
> takes some time to process an interrupt, wakeup the process and schedule
> it to run on the CPU. 10-30 microseconds is not unreasonable.
But 2 operations can be done in 10 microseconds?
and why is there that inconstancy? Why sametimes 10 and sometimes 30?
In which points of implementation it happens?
GolovaSteek
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