Unix Technical Digest V2 #6

[Heiby]

Unix Technical Digest       Fri, 24 May 85       Volume  2 : Issue   6

Today's Topics:
                  AT (IBM) XENIX Performance Limits
                           CTS/RTS Thanks.
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Date: Wed May 22 16:40:08 1985
From: ihnp4!dicomed!mecc!sewilco
Subject: AT (IBM) XENIX Performance Limits

I've been running an Apple Lisa 2/10 with Xenix 3.0 for the past
year.  Therefore I can't speak about an IBM AT, but since I've
been straining the machine for months I can point out some
problems with Xenix which might apply to the AT.

The configuration is:
	Lisa 2/10 with 1M RAM.  A 2/10 comes with 10M disk
	drive built in (slow disk, but no specs published),
	has two serial ports, and it does have an MMU.  I
	also have two pieces of hardware from Tecmar; a
	four-port serial card and an 85M disk (1.21 Mbyte/sec,
	and I think 15ms access).  Oh, yes..a Lisa uses a
	68000 at 5Mhz clock rate (not the 8Mhz in a Mac).

As always, apparent performance depends on how you use the machine.
Here there are four terminals, three of them active all day with
mostly order processing (type some in, one or two records are
changed, the screen is updated, and repeat).  Most reports and
other things with require much processing are done at night.

At present, our limit is FOUR active users, though we have hardware
for seven or eight (6 serial ports and 2 users can share Lisa
screen).

All terminals are using SMC BASIC.  SMC says their recent BASIC
interpreters use UNIX "shared text", so only one copy of the
interpreter would be in memory for all terminals.  Program and
data memory per user are small, so any needed swapping would be
fast.  With one megabyte of RAM, a few more than four users
should be no problem with our configuration and applications.

Our problem is that each file in use within SMC BASIC is also
a Xenix "open file".  Each file which is in use takes up one
entry in the kernel's "inode table", and each file which each
user has open takes up an entry in the kernel's "file table".
With five users, each with 16-18 open files, the "file table"
gets too full.  Even if the table is not completely full, it
is full enough that system daemons (ie, printer spooler) can't
open files.  The "inode table" might also get rather full if
the open files are all different files.

So although our Xenix does let us log in with as many terminals
as we have hardware, if we try to use more than a few of them
to run our application programs we run into the limits imposed
by the sizes of those two tables.  The Xenix manual does show
a "config" program which would allow those limits to be changed,
but SCO says config is not available for the Lisa.  You should
check that it is available for whatever machine you have in
mind.  Otherwise you'll be stuck with whatever parameters SCO
thinks are good for you even if you know what needs to be tuned
in the system.

Scot E. Wilcoxon	Minn. Ed. Comp. Corp.     circadia!mecc!sewilco
45N03',93W15'	(612)481-3507 {ihnp4,mgnetp,uwvax}!dicomed!mecc!sewilco

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Date: Thu, 23 May 85 17:23:58 BST
From: seismo!ukc.ac.uk!mcvax!has
Subject: CTS/RTS Thanks.

    Firstly I would like to thank all the people who replied to my request
concerning  using CTS/RTS on  dz lines.  Since I  have to ask specifically
for access to mail off site here at ukc it is not possible for me to thank
people individually.
    I will most likely use the CD and DTR lines and set the stty modes, as
although I  could get  the source and  alter the  drivers I have been told
that I would loose  system support from  the central  Computing Labs. if I
altered things like that.  That is life I suppose !!
    Thanks  again, if anybody out  there ever  wants anything that I might
help with...
  Howard Shaw.  Physics Laboratory U.K.C.  ...!ukc!has

PS: I hope it is "proper usage" of the net to reply like this but there
    is not a lot else I can do.  has.  [Ed note:  Grey area.  RWH.]

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Ronald W. Heiby / netnews at wnuxb.UUCP | unix-request at cbosgd.UUCP
AT&T Information Systems, Inc., Lisle, IL  (CU-D21)