🚀 go-pugleaf

Kazimir Kylheku <c2a192@ugrad.cs.ubc.ca> wrote:
>>preemptive multitasking is _less_ efficient than nonpreemptive
>>multitasking, because of preemption overhead.  many supercomputers run
>
>The overhead is insignificant. One hundred clock ticks per second
>are nothing to a modern CPU. Even the Commodore 64 had a 60hz clock
>tick for updating the clock and hooking in user interrupt routines.
>You don't know what you are talking about.

Besides, cooperative systems still have clock interrupts, too!  The
only extra overhead added to the preemptive interrupt handler is
something like this:

	if ( HigherPriorityTaskIsRunnable )
		Yield();

Basically, as far as overhead goes, all a preemptive system is really
doing is making sure that the process doesn't go too long without calling
the yield function.   There's no reason for it to have any more overhead
than a cooperative system, *unless* you are comparing to a cooperative
system that is running an application that is refusing to yield.  The
cooperative system will execute

	unsigned long x, y;

	for ( x = 0; x < MAXLONG; x++ )
		for ( y = 0; y < MAXLONG; y++ )
			;

more efficiently than the preemptive system.  But for cooperative systems
where the applications actually cooperate to keep the system responsive,
the preemptive system will be as efficient.

--Tim Smith