🚀 go-pugleaf

scott goehring <sgoehrin@copper.ucs.indiana.edu> wrote:
>>True.  Pre-emptive is more efficient and smoother, which is why it was
>>added into 95.
>
>preemptive multitasking is _less_ efficient than nonpreemptive
>multitasking, because of preemption overhead.  many supercomputers run

You've ignored the extra overhead in cooperative systems that is
required to keep the system responsive.  Consider an extreme case:
two compute-bound processes.  A modern preemptive schedular will
settle into a round robin with these with a very large time quantum,
and the overhead will approach zero.

On a cooperative system, both of these processes have to repeatedly
give up the CPU to the OS, just in case there might be an interactive
process that needs the CPU.

Basically, optimal scheduling requires taking into account the *global*
state of the system.  Cooperative systems make each process, which only
knows the *local* state of the system, make scheduling decisions. 

There are some tricks that could be used to cut the cooperative overhead,
but the major makers of cooperative systems (Apple and Microsoft) manage
to keep overlooking them.

--Tim Smith