nanosleep() accuracy

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.

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
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