Performance of various versions of UN*X

[Doug Gwyn <gwyn>]

> I would like to know how System V rel. 2 compairs with BSD 4.[12].
> We are running System V rel. 2 on a VAX with 4M ram, three rm05s,
> one rm03, and five DZs. This system gets REAL slow with 25 to 30 users,
> beside crashing about once a week. I would like to know if BSD 4.[12]
> would be faster (and maybe not crash).

All performance studies I have seen show that under conventional
workloads UNIX System V Release n and 4.nBSD have comparable
throughput.  Each is faster than the other in specific areas.

4.1BSD is pretty stable.  4.2BSD has a faster file system but degrades
worse under heavy load than 4.1BSD (this problem is being worked on).
I would not guarantee that these systems would run a week without
crashing, though; that depends on lots of things (like whether you have
flakey hardware and whether you are using buggy kernel facilities).

One thing to avoid on UNIX System V Release 2 is switching line
disciplines.  This is known to cause crashes.  Have you analyzed
your crashes to see what is causing them?

5 DZ11s will certainly take a lot of CPU, especially if you have many
users of screen editors.  A dramatic improvement for any such UNIX
System V is to use the KMC11B I/O processor to offload the terminal
processing (input canonicalization, pseudo-DMA, etc.).  This is the
first thing I would try.

Note also that with only about 3Mb of user process RAM and 30 users,
each user only has 100Kb of memory for his processes before swapping
occurs.  You should use the excellent system analysis tools of UNIX
System V ("sag", etc.) to determine where your bottlenecks are.  More
main memory may help.