p_nice, and scheduling

[mike.rice%rand-relay at sri-unix.UUCP]

From:  Mike.Caplinger <mike.rice at rand-relay>

We are (unfortunately) in the position of running a lot of niced
background compute-bound processes on our 4.1 11/750.  Usually about 3
of these jobs are running at a nice of (usually) 4.  Subjectively, it
seems that these jobs are killing the system, in spite of their
niceness.  I theorize that it's because the system is constantly
swapping them in and out as interactive jobs become ready to run and
then wait for input again.

Exactly what effect does nice have in the scheduler?  I've looked at
the code, but it isn't immediately obvious.  Why did UCB change the
default nice (10 in /bin/nice) to 4 in the builtin nice in the Cshell?
If I change the Cshell default back to 10, will that help, hurt, or
make any difference?

If it helps, the machine config is a 750 with FPA, dual Unibus, 1 ra81,
and 4 Meg of memory.  The average size of the background processes is
about 1 Meg, sometimes higher.

Reply to me at mike.rice at rand-relay, and I will summarize to the net.
Thanks much, everybody.