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From: ForthNet@willett.pgh.pa.us (ForthNet articles from GEnie)
Newsgroups: comp.lang.forth
Subject: Multi-tasking and Multi-user
Message-ID: <2920.UUL1.3#5129@willett.pgh.pa.us>
Date: 25 Jun 91 02:31:07 GMT
Organization: (n.) to be organized.  But that's not important right now.
Lines: 32

Category 3,  Topic 14
Message 24        Mon Jun 24, 1991
D.RUFFER [Dennis]            at 00:22 EDT
 
I participated in the Real Time working group at the Rochester Forth
Conference this last week, and the subject of multi-tasking schedulers came
up.  The basic schemes discussed were round-robin and pre-emptive schedulers. 
The conclusion was that both have their advantages and disadvantages.

The pre-emptive schemes have more general overhead when switching tasks, and
the timing of events (when multiple tasks are active) can be difficult.  The
biggest advantages are that the time from interrupt to task activation is very
short and predictable and the task switch overhead can be reduced by
minimizing the number of times you switch.

The multi-tasker has the lower task switch overhead, but it is always
switching tasks so the more tasks you have the more total overhead you have to
deal with.  You can determine when you will let other tasks have control, but
you do not know how long you will be gone when you do the PAUSE.  Also, the
time from interrupt to task activation is not predictable, since you must wait
until the current task releases the CPU.

Each has its tradeoffs, but the round-robin is certainly easier to implement
than the pre-emptive schemes.  Obviously, we did not resolve the debate
between the techniques, but we did learn more about how the other works.

   {B-{)>   DaR
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