Path: utzoo!attcan!uunet!jarthur!usc!zaphod.mps.ohio-state.edu!swrinde!emory!hubcap!rjc
From: rjc@cs.ucla.edu (Robert Collins)
Newsgroups: comp.parallel
Subject: Re: Ease of programming (was Re: Acceptable efficiency factors)
Message-ID: <9554@hubcap.clemson.edu>
Date: 3 Jul 90 17:22:16 GMT
Sender: fpst@hubcap.clemson.edu
Lines: 67
Approved: parallel@hubcap.clemson.edu

In article <9549@hubcap.clemson.edu> philip@Minnie.Stanford.EDU (Philip Machanick) writes:
>
>In article <9521@hubcap.clemson.edu>, argosy!ian@decwrl.dec.com (Ian L.
>Kaplan) writes:
>>   Perhaps the difference in the execution efficiency between the Intel
>> cube (an MIMD machine) and the CM-2 (a SIMD machine) is due to the
>> fact (not doubt hotly contested) that SIMD systems are easier to
>> program.  [...]

>I have recently had an experience of porting a program originally
>written for a vector architecture to a shared-memory (MIMD) architecture.
>Although the original program was written in C, [editted] . My remodelled
>program was written in C++, using object-oriented programming [editted]
> There were two major reasons
>for this approach: objects aggregated related data, which made for
>better caching performance, and object-oriented programming made the
>program more easily modifiable (for example, we were modeling gases,
>and it would have been a relatively trivial change to introduce
>subclasses to model a multiple-specie gas). Another benefit was I used
>subclassing to represent boundary conditions (a cell representing a
>region of space was subclassed to represent walls etc.). Sure, I had to
>worry about synchronization and load balance, but I found the resulting
>program much easier to understand. Synchronization bugs were trivial
>compared with the problems I had with understanding details of the
>original program.

Philip, you say lots about the advantages of programming in C++ vs.
FORTRAN, but nothing about programming MIMD vs. SIMD.  Ian is right,
SIMD is very much easier to program.  Imagine what would happen if
you programmed a SIMD computer from C++!  I have been doing this
for a couple of years now, and never want to go back to C, and
never want to write a MIMD program.  If I ever have to write a
program for a MIMD machine, I hope I can do it in a data parallel
language.  (I have become convinced that the best method for
programming in many situations is a data parallel model, built
on top of MIMD hardware.  This gives us the best of both worlds:
ease of programming, and fast execution of conditionals.)

rob collins
























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rjc@cs.ucla.edu	                    CM++ on the CM2:  The only way to fly.
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