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From: rb@cci632.UUCP (Rex Ballard)
Newsgroups: comp.arch
Subject: Re: Will the Karp Problem Be Solved?
Message-ID: <747@cci632.UUCP>
Date: Fri, 12-Dec-86 14:55:39 EST
Article-I.D.: cci632.747
Posted: Fri Dec 12 14:55:39 1986
Date-Received: Mon, 15-Dec-86 04:51:11 EST
References: <3302@curly.ucla-cs.UCLA.EDU>
Reply-To: rb@ccird2.UUCP (Rex B)
Distribution: world
Organization: CCI, Communications Systems Division, Rochester, NY
Lines: 39
Keywords: parallel processing
Summary: It's a rigged game.

The Karp challenge, at first looks like a very simple challenge
to beat.  But after looking at the rules more carefully, I could
say it's a "rigged game".

There are two analogies here.  In the first analogy, the most
popular, you are building a house.  If it takes 1 man 1 year
to build the house, but it takes 2 men 6 months to build the
house, then it should take 365 men 1 day to build the house,
and 3650 men, little more than an hour to build the house.
Karp has generously not limited the number of processors
required to get his 100 fold increase, but I can referr to
the "mythical man-month" for the problems with such increases.

In the other anology, we have an assembly line.  In this case,
it does become possible to organize a group more efficiently,
and productivity does go up.  Because all of the workers are
able to do work at the same time, and time is saved searching
for tools, it is "theoretically possible" for the line to
build a car that takes 1 man-year to build in an average of
1 day.  This is because many portions of the pipeline are
also parallel, for example, the four wheels can be mounted
at the same time.

Karps test however, limits the number of tools available,
and then asks for the actual time required to build 1 car.
While it might still be possible to build the car in a month,
because only one "cylinder maker" is allowed,..., even with
365 men, the increase will not approach 100-fold.

Our company, like several others, does have distributed processing
networks incorporating well over 1000 processors, and yet the
speed-up factor for a single job, running through the network,
is not significantly faster when compared to the actual execution
time (less OS overhead) of a single processor system.  The important
difference is that the system can handle 1000 jobs before serious
degradation over single job performance occurrs.

If one carefully reads the rules, they will find that Karps test
is quite simply a "rigged game".