Problems with vpix under xenix2.3.1

[Chris Lewis]

In article <105 at accsys.acc.uu.no> ivar at acc.uu.no (Ivar Hosteng) writes:
>> All works well except that once vpix is running xenix seem's
>> to get less than 10% of the time-slice??

>That's because VP/ix has to poll all devices that DOS is using. This
>takes a lot of time, and the result is that the rest of the system is
>suffering. I had the same problem myself but found no solution.

>> --> So, I though, start vpix with a *nice* setting!
>>     ie.: nice -7 vpix
 
>> Great! But now both seem to run in a burst fashion, ie. first
>> vpix is busy for say 7/10th's of a second then xenix? I can't
>> figure out what the hell is going on - it's almost like vpix
>> regularly say's *sleep 1*!

Question:  Does your VP/IX appear to be accumulating CPU time faster
than real time?

You can prove that VP/ix polls simply by seeing if the process time
via "ps" goes up even when your VP/ix session is simply displaying a
DOS prompt.

I was told (by an ISC employee) that the 386/ix scheduler attempts to 
circumvent the nastiness of VP/ix polling by artificially diddling the
clock ticks being charged to the process.

You see, most UNIX schedulers dynamically increase the priority of a process
on each I/O that it performs, and decreases it proportional in some fashion
to the CPU the process uses.  Thus if you zap the process times in the
proc area up, the priority will go down.  Sort of ass-backwards if you
ask me.

At one time, (perhaps 386/ix 1.0.3 or ..4), there was a version of VP/ix that
didn't poll.   No CPU "leakage".   Ran like a bat out of hell.  Don't know
why they went back to the polling version (presumably some brain-dead
DOS application package requires it).

Further, all should be aware that VP/ix is both a memory and CPU hog.
As a general rule, you can get quite reasonable performance if you allow
1 megabyte of physical memory for each simultaneous VP/ix session, plus
sufficient memory for the kernel (plus something for the UNIX processes
to live in).

On 386/ix, 2 VP/ix sessions aren't too bad in 4Mb (provided that the
t'other guys aren't running cc, troff, rn, jove or perl).  Things get 
much better when you get to 8Mb or more.
-- 
Chris Lewis, R.H. Lathwell & Associates: Elegant Communications Inc.
UUCP: {uunet!mnetor, utcsri!utzoo}!lsuc!eci386!clewis
Phone: (416)-595-5425