Wed, 19 Apr 2000 Adi Sudewa wrote:
> 1. What is the highest and lowest priority of a task ?
> Can a thread change its priority dynamically ?
I'm not enough up-to-date with the current releases to give numbers here.
Anyway, in general, don't mess too much with dynamic thread priorities and that
kind of stuff! It can complicate things a great deal, and normally, you only
need it in systems with multiple CPU intensive threads, and to "save" bad
designs. I believe it's more fun in theory than in real life! :-)
> 2. What is the difference between one-shot clock and periodic clock ?
> (There's no explanation in the manual)
It has to do with how the hardware timer is used to generate the periodic
scheduling rates. One-shot mode means that the scheduler reprograms and restarts
the timer for each scheduling point, while in periodic mode, the timer is set
to a fixed rate to avoid the reprogramming + restart overhead. Obviously,
periodic mode requires a sensible relation between the scheduling rates, if
there's more than one periodic task running.
> 3. Can I call a Linux system call ? Of course this will screw up the hard
> real-time constraints, but in case ...
Some calls are safe, but most aren't as a result of the standard Linux kernel
being preempted by RTL threads and IRQs. The preferred way in most cases is to
use bottom halves, and have the RTL threads trigger them when needed - the
delay will be there anyway, as most standard kernel calls affect only non-RTL
stuff.
David Olofson
Programmer
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