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Priority in SPoC
Denis A Nicole wrote:
> Anyway, the real reason for the message was to discuss SPoC's
> implementation of PRI. The SPoC scheduler essentially uses coroutines; it
> is not preemptive. When it gains control, which includes every
> communication and PAR, it uses two queues, high and low priority, as in
> the transputer. The high priority queue is always run if possible.
> Without external communication, a high priority process can _only_ become
> ready at a scheduling point, so this model ensures that there is never a
> high priority process waiting on a low priority one. The scheduler has no
> preemption, so this guarantee cannot be provided for _external_
> communications triggering a high priority process.
Have you any comment to make on how expensive it would be to detect
priority conflicts? As I have said several times, I suspect that it
would add an unacceptable overhead for software implementations. But you
are in a far better position to know.
Also I wonder whether you have any gut-feeling about whether in
principle SPoC should signal "critical error: priority conflict" on our
little test programs. On safety grounds.
A E Lawrence, MA., DPhil. adrian.lawrence@xxxxxxxxxxxxxx
MicroProcessor Unit, 13, Banbury Road, Oxford. OX2 6NN. UK.
Voice: (+44)-1865-273274, Fax: (+44)-1865-273275