On Thu, 16 Sep 1999, Stuart Hughes wrote:
> Waking up a user space task blocked on an rt-fifo read work very well
> for soft real time where you want better than 10ms intervals (an RT task
> does periodic rtf_puts()). You can also use the RTC device in the linux
> kernel, but be warned I used to see occasional lockups when I used the
> RTC and RTL. Note that you *will* miss whole periods, as your user
> space process will go out to lunch when the Linux kernel is working,
> even if you use SCHED_FIFO etc.
I have noticed that with RTC when I have a process blocked on read and other
background process doing something (e.g. calculations), the RTC interrupt
does NOT cause re-schedule, even if the waiting process has RT priority. It
is probably because RTC uses fast interrupt handler. The readinf process is
woken up on next timer tick.
I have not tested if writing to FIFO from kernel wakes up wating task
(reschedule) immediately, but I hope so.
--
Tomek
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