UNIX Performance Penalties

[Wm E. Davidsen Jr]

In article <652 at anacapa.NCEL.Navy.Mil> greg at anacapa.NCEL.Navy.Mil (Gregory K. Ramsey) writes:

  Forgive the long answer, it's shorter than the question.

| I would like to ask the net on their learned opinions regarding
| the performance penalty of a 386/486 UNIX vs.DOS.

General guidelines, unix vs dos:

  if you have a job doing a lot of disk i/o it will be
somewhat faster on unix due to write back buffering. 

  If your application is compiled for 32 bit unix using a good
compiler, and uses 32 bit int data, you will get about 2:1 (I didn't
believe it until I measured it either). For programs not using 32 bit
data the DOS compilers are slightly better than the unix compilers.

  Programs which in DOS write directly to the screen are a lot faster
than unix screen update, but in many cases, particularly with text
modes, the update is faster than you can read the data and it makes no
diference.

  Running DOS programs under UNIX makes screen updates slower. In pixel
mode figure VP/ix as 2:1 slower than DOS, DOSmerge 2:1 slower than that.
I base this on fractint in 640x480 mode, other program will give other
results, but the order of performance is almost always the same.

	[ they do CAD ]
| 
| We have 300Mbyte 28ms drives and VGA and expect to stay with this
| for all the new machines.

  This is as slow as I would want to go. Spend the money and get 16-18ms
drives on the new machines, and you will be happier.

| Our idea is to upgrade everyone to 386 or 486 machines and
| network them with some variety of UNIX & X-windows with one or
| two servers and 10-15 clients.

  I'm not totally sure what you really mean by that, and I'm not
convinced you do either. Remember that the display is the server and the
process the client. I presume that you mean you will put 10-15 displays
on 1-2 machines. That will give lousy performance compared to DOS.

  If you mean fileservers, it will save money and system admin time, but
hurt performance. You might look at a dedicated NFS server, too.
Companies like Epoch have very cost effective storage.

| My main question is what performance degradation (if any) will my
| users see considering all the overhead that UNIX, X-windows,
| network communication and system management processes will bring
| along.

  Given the same number of users (one) performance should be a good bit
better. CAD programs really respond to more memory and use of 32 bit
data. Running X you should figure 8MB for the system, 2-4MB per user.
Stop gasping, memory is down under $50/MB for 1MB SIMM/SIPP. That will
help performance more than almost anything else.

| Will the 286 (8 & 12 Mhz) users see an apparent performance
| increase, status quo or decrease.  The users perception is what I
| am really interested in here, but if you have any (or know of
| any) numbers that would really be appreciated.

  On a system with adequate memory, you could put two users on a 25MHz
386, and doing the same kinds of things in CAD I would expect they would
think they went to heaven.

| What about the 386 users?

  The UNIX version will be faster, but you can load it down. User input
is a low load, and you can put a bunch of people on with good response.
When they ask for redraw, then you see performance hits for multi-user.

  Of course I assume you have a 387 in each machine.

| Any comments on my questions or on any related ideas would be
| very much appreciated.

  With 486 prices falling I would suggest you go that way. At equal
clock speed the 486 is 2-3 times faster than a 386. The cost factor is
rarely more than 20% of the total system price (CPU, memory, display,
disk, network).

  You might also look at getting color X_terminals instead of VGA
displays. They have higher resolution and will be faster than the
builtin display in most if not all cases.
-- 
bill davidsen - davidsen at sixhub.uucp (uunet!crdgw1!sixhub!davidsen)
    sysop *IX BBS and Public Access UNIX
    moderator of comp.binaries.ibm.pc and 80386 mailing list
"Stupidity, like virtue, is its own reward" -me