Path: utzoo!attcan!uunet!lll-winken!lll-tis!helios.ee.lbl.gov!nosc!ucsd!ucbvax!UBVMSC.CC.BUFFALO.EDU!PSYDAVE
From: PSYDAVE@UBVMSC.CC.BUFFALO.EDU (Dave Straitiff)
Newsgroups: comp.os.vms
Subject: RE: MPW_HILIMIT
Message-ID: <8806241250.AA08692@ucbvax.Berkeley.EDU>
Date: 21 Jun 88 06:12:00 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
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   Dan Esbensen who wrote the Dynamic Load Balancer and the booklet
you are refering to gives a couple reasons for raising MPW_HILIMIT.
This parameter tells VMS to dump the whole modified page list into the
page file when this number is reached.  That's a lot of I/O overhead.
Most of what Dan recommends is oriented towards systems with a large
amount of memory.  You are not really losing any memory by setting
this high, but rather keeping more pages around in physical memory.
The modified page list is purged to replentish the free page list.  
What you are doing is keeping a lot more modified pages around in the 
hope that MPW_HILIMIT will be reached less often and therefore prevent 
a number of hard page faults and I/Os.  Many pages will be immediately 
faulted back in.  The idea is to make it a soft fault and not a hard one.

   Testing a high number is not going to hurt you.  It is worth giving a 
try.  As in all tuning, it is based on your applications and hardware. 
This concept may or may not help in your environment.  Too low of a value 
will probably hurt though.  Digital's numbers are not always a good 
reference for what is a reasonable value.  Many defaults are the same on
Vax 730s and 8800s, they are usually only best guesses.  The new version 
of autogen may correct some of this by collecting stats on a running CPU
for later tuning.  As the title says, "Rules of Thumb", 15% may not
be the right number for you.  Try it high, try it low, try it inbetween,
and see what it does for you.  A last note is on MPW_WAITLIMIT, it should
be the same as MPW_HILIMIT.  The system could deadlock if MPW_WAITLIMIT
was lower than MPW_HILIMIT.

   Tuning can be a lot of fun and very informative, but it usually only
produces a marginal increase in performance.  Poor or excessive tuning 
may even hinder performance.  I'd approach it with a little reservation.

				Good Luck!

				Dave...


============================================================================
 David M. Straitiff                  Bitnet:   PsyDave@UBvms
 Computer Resource Manager           Internet: PsyDave@UBvms.cc.buffalo.edu
                                     Phone:    (716)689-8093
 Speech Research Laboratory
 Department of Psychology
 State University of New York at Buffalo
 Buffalo, New York  14260
============================================================================