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From: jxf@orion.cis.ksu.edu (Jerry Frain)
Newsgroups: comp.sys.mac.system
Subject: Re: Preemptive scheduling
Message-ID: <1991Jan16.214809.25818@maverick.ksu.ksu.edu>
Date: 16 Jan 91 21:48:09 GMT
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Before you read my article, let me just say that I _do_ like the Macintosh.
I own one, and I like it.

The important thing to keep in mind here is that there is _always_ room
for improvement.  If everyone was so against improvement, we (as a Mac
community) would still be using Finder 1.0 on the original Mac.

Now, if you are not completely bored and tired of endless discussion over
the prospect of preemptive scheduling for the Mac, then please read on,
otherwise hit "n" now.

heksterb@Apple.COM (Ben Hekster) writes:
>jxf@altair.cis.ksu.edu (Jerry Frain) responds:

[ Ben complains about his mouse not moving fast on his workstation ]

>> I always find this argument quite humorous, since I do all of my work
>> at work on a Sun workstation using X, while I do all of my work at home
>> on a Mac SE/30.

>I find it surprising that you find my observation humorous.

I was surprised that a person who has used a preemptive scheduling
environment would not like it more than its cooperative counterpart.

[ explanation of poor performance on HP 9000 workstation ]

Sounds like your system needs to be reconfigured.  Anything that has
difficulty doing what you described ought to be fixed or junked.

>> Shove a floppy in your disk drive on your Mac and move your mouse around
>> and tell me how your Mac is *so* responsive (IIfx owners may be exceptions
>> to this test).

>I'm not sure I understand what point you're trying to make here.

How about "mouse response on the Mac goes away during volume recognition."

>                                                                 Presumably
>the assumption is that when a user inserts a disk, he wants to mount the
>volume, and at that time doesn't really care for his Mandelbrot background
>task to run for another 1000 iterations.

I don't have a mandelbrot background.  I have a mouse.  Perhaps I have
inserted the floppy so that I may copy a file to the floppy disk.  Haven't
you ever tried to open the folder that the file is in while the Mac is
trying to figure out what the name of your disk is?

The jerkiness of the mouse caused by volume recognition is just damn
_unnecessary_, and irritating.

>                                         Since the disk-mounting is alredy
>running at the highest priority possible (nothing is preempting it) I'm not
>sure I understand what good a preemptive scheduler would do here.

Gee, isn't that entirely against the philosophy of the Mac's cooperative
scheduler?  Isn't the interactive user supposed to get good response
time *no matter what*?  Your argument above is what most people use to
argue *against* preemptive scheduling, the idea that the interactive
user might not get prompt responses!

You cannot tell me that during the time period that volume mounting is
taking place, that the CPU is _really_ busy.  Probably less than 1/1000
of the delay experienced is actually due to the fact that the CPU is
too busy to move your mouse.

>	The underlying premise is that getting the disk mounted as quickly as
>possible is more important than moving the mouse.

I think that *both* mouse responsiveness and volume mounting should be
provided at the same time.  It can be done.  Why do you not desire this?

>	As an aside--how many of those ninety processes were running to
>support the multitasking?

What?  Are you kidding?  The answer is "none."  The scheduler is part of
the operating system, which is not represented as a process.

There are, at this very moment, 126 processes on this workstation I am
posting from.  Most of these processes (73) are concerned with network
services provided by this machine.  Nfs, yellow pages, etc.

The rest of the processes (53) are user processes.  There are currently
six users logged on this machine.

The responsiveness of my mouse pointer (or anything else for that matter)
is instantaneous.  Just like my Mac.

Have a nice day.

 --Jerry

--
Jerry Frain -- Systems Programmer               Kansas State University
                                        Department of Computing & Info Sciences
Internet : jxf@cis.ksu.edu                         Manhattan, Kansas
UUCP     : ...!rutgers!ksuvax1!jxf