Problems with vpix under xenix2.3.1

[Ivar Hosteng]

> 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*!

I'm not sure why this is happening, but I think it's the swapper that
executes the VP/ix task and because it has a higher nice factor it is
halted more often. You must remember that most of the Xenix tasks uses
blocking I/O and thus is giving up the rest of its slice. Since VP/ix
is polling all devices there is no way for the swapper to know when
VP/ix is waiting for I/O. This makes the swapper execute VP/ix until
its maximum time slice expires.

> This simple test shows up the problem - perhaps some one out
> there with a similar configuration could give this a try - and
> offer some kind of explanation or consolation.
> 
> - login twice.
> - in one window start vpix -> nice -7 vpix
> - type the following in the other window:-
> 	while true
> 	do
> 	sync
> 	done
> 
> your fixed disk should start to regularlly flash - now switch
> to the vpix window and observe what happens to the poor task
> running in the back-ground. If you then switch to a new window
> things work fine again - but as soon as you go back to the vpix
> window the(task in the back-ground becomes sluggish!
The reason the system regains the speed when you switch to a new window
is that when VP/ix is not in the current window it stops executing.
This is in my opinion the weakest side of VP/ix and makes it unusable
for my purposes.  VP/ix runs fine on a external terminal but then you
only get a monochrome screen.

> Would appreciate any hints or advice.

I have no solutions to your problem but I hope this explains why it
goes so bad. Maybe someone at SCO is reading this and can give a more
concise answer.

Ivar Hosteng, Advanced Computer Consultans, Oslo, Norway
	- ivar at acc.uu.no