Just a bit of musing

[Chris Gray]

:It is my understanding that many OSs that implement multi-processing will
:allocate one CPU for the OS and the rest of the available units to
:application
:threads.  NT 3.51 does this as well as many Unixes.  I thought OS2 used
:this
:model also.  (please correct me if I'm wrong)

In the Sun world, this has never been true. SunOS didn't use SMP's very
well, because when anything needed kernel work, a single global lock kept
everyone else out of the kernel. Even then, there was no CPU reserved for
the kernel. Under the newer Solaris, the locks within the kernel are of
much finer granularity, so several CPUs can be executing kernel code at
the same time. My understanding is that IBM's AIX went through similar
changes (AIX 3.5 didn't support SMP, but AIX 4.1 was a rewrite, and is
much like Solaris on SMP's). I'm not sure about HP's HPUX, but the dual-CPU
machine beside my desk at work doesn't seem to suffer any problems, and
most certainly can have both CPU's busy doing user work.

:It is also my understanding that NT 4.0 uses a different model and
:implements
:"load sharing" as you define it above.   I have heard rumors that Digital's
:64-bit Unix
:uses the "load sharing" model.  Does anyone have any info on this?

I'd be surprised if anyone wrote an operating system which reserved a CPU
for the OS itself. However, it *is* MicroSoft being talked about!!! :-/
DEC is pretty good at software, so they should be able to get it right.
We haven't ported our stuff to Alpha's yet, however, so I have no
direct experience with them.

--
Chris Gray   cg at ami-cg.GraySage.Edmonton.AB.CA