Curt Sampson wrote:

 > If the machine is also used interactively, load is a problem even
 > if you do have enough memory. When my personal workstation at home
 > was a 3/60, I used it as the router as well, and the screen would
 > freeze for a couple of seconds whenever another machine on the
 > network started doing a large transfer.

That's not entirely surprising:  The interrupt priority of the serial
ports on Sun hardware is close to the highest possible, on the grounds
that if someone is using a serial console they might wnat to see error
messages emitted as the system dies, so it makes sense to pre-empt anything
else with tty interrupts.

That means that whenever the serial interrupt service routine needs to do
something, everything else has to share the *second* bite of the CPU 
cherry.  That's one of the main reasons why serial ports on Suns suck
so hard, although there are pleny of other reasons if that one doesn't
sound good enough :-)

The entire system stops for text console output too, btw, for precisely
the same reason.  (when I say "entire system", I mean that text output
on the console overrides SCSI and network interrupts!)

    - mark

---
Mark Newton                               Email: newton@communica.com.au
Systems Engineer                          Phone: +61-8-8373-2523
Communica Systems                         WWW:   http://www.communica.com.au