Vax 11/780 performance vs Sun 4/280 performance

[weiser.pa at xerox.com]

Andy Rosen writes:
"Some time ago I saw a Sun 3/280 with a load average of 17+.  There were
17 'extra' jobs running.  I don't know what they were doing (they weren't
mine), but there was no [noticable] degradation in response time at all."

I just tried this on my Sun-4/280 by running 30 cpueating processes.
("while(1);").  Sure enough, even with the load at 30, I got much better
response than I did with only 20 of the little 50 ms sleeper programs I posted a
day or so ago.  One way to interpret this is that when Sun's scheduler knows
that it has 30 processes on the queue, it does a better job of sharing the
limited resource of contexts, than if it thinks there is nothing to do, but
every 50ms 20 jobs all suddenly leap up and call for attention...  But I don't
know for sure.

Perhaps the 50ms. sleeper test is a red herring, and that pathological state is
not one that is ever seen under normal user loads.

But in any case, we got on to this topic by something a DEC salesperson said to
discourage Sun purchaes, and I think, because the knee is real but perhaps only
in pathological cases that no one really cares about, we have exactly a
salesperson sort of "fact".  Mystery resolved.

-mark