Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!uwm.edu!linac!att!cbfsb!cbnewsb.cb.att.com!feg
From: feg@cbnewsb.cb.att.com (forrest.e.gehrke)
Newsgroups: comp.os.msdos.programmer
Subject: Re: Performance penalty from EMM386 ?!?!
Message-ID: <1991Jun26.120951.18540@cbfsb.att.com>
Date: 26 Jun 91 12:09:51 GMT
References: <6455@tellab5.tellabs.com>
Sender: news@cbfsb.att.com
Organization: AT&T Bell Laboratories
Lines: 41

In article <6455@tellab5.tellabs.com> neuron@tellabs.com (Don Graft) writes:
>Respected net people, I'm having a problem with EMM386.SYS (under DOS 4.01
>and now 5.0) that defies logic.  I have a simulation program written in
>Borland C++ small model. It just does a 4th-order Runge-Kutta system of
>ODEs to simulate a series of masses and springs. It uses the Borland
>software floating point support (i.e., no math chip). The Borland BGI
>stuff is used to display results to a VGA graphics mode.  There is no use of
>expanded memory or anything fancy going on with memory management (that I
>know of).
>
>When I run this simulation without EMM386.SYS installed, it blazes.  When I
>install EMM386.SYS with the noems switch, it crawls. We're talking 45 secs
>versus 20 seconds for a typical run; this is no quibbling about a few
>percent.

Having spent several hours trying to get HIMEM.SYS and EMM386.SYS to
give me as much usable low memory as QEMM386 does (both with dos=high)
and, BTW I nearly got there-600KB vs 632KB, I can confirm the big
slowdown you encountered.  Not only does floating point emulation
take a big hit but so does display writing--something of the order
of 50%.

QEMM also encounters this problem but not nearly to this extent--about
10 to 15% when using programs compiled with MSC or Borland's C.

If you can compile your program with MSC, try their Alternate Floating
Point emulator, you will encounter no slowdown with it, but with
less accuracy.  This applies only to floating point emulation.  
If you had a coprocessor, you would not see any slowdown, but display 
writing would still be affected.

Tests I have done with floating point programs compiled with the
Zortech v2.1 C compiler show no slowdown with their emulator when
using expanded memory managers, but their emulator is much slower
to begin with.

These results appear to point to the compilers introducing a problem
in programs when working with expanded memory managers, and not to the
expanded managers themselves.

-Forrest Gehrke feg\@dodger.att.com