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 = 300000;
req.tv_sec = 0;
nanosleep(&req,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.
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.
Michal
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