Re: Parallel FIB

From	anton@mips.complang.tuwien.ac.at (Anton Ertl)
Newsgroups	comp.lang.forth
Subject	Re: Parallel FIB
Date	2013-05-02 14:13 +0000
Organization	Institut fuer Computersprachen, Technische Universitaet Wien
Message-ID	<2013May2.161355@mips.complang.tuwien.ac.at> (permalink)
References	<62150201988434@frunobulax.edu>

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mhx@iae.nl (Marcel Hendrix) writes:
>I couldn't find a use for a 4th core, but the speedup is 
>already about 7 times (2 times for a pure algorithm compare).

Hmm, so you expand the doubly-recursive version of fib so that a few
recursion levels are optimized, turning it into a version with three
independent calls; because the calls do not perform the same amount of
work, you see only a speedup of 2.  Given that

phi^2 = phi+1

it's not surprising that you see a factor of 2.  I would expect

n 5 - fib
n 6 - fib

together to take the same amount of time as

n 4 - fib

So do the former calls in one thread, and your program will probably
run faster (wall-clock time) on 2-core CPUs.

Hmm, I wanted to start out saying that doing such a trivial
parallelization of a ridiculously inefficient algorithm is pretty
pointless, but apparently there are still some insights left.

- anton
-- 
M. Anton Ertl  http://www.complang.tuwien.ac.at/anton/home.html
comp.lang.forth FAQs: http://www.complang.tuwien.ac.at/forth/faq/toc.html
     New standard: http://www.forth200x.org/forth200x.html
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Parallel FIB mhx@iae.nl (Marcel Hendrix) - 2013-05-02 01:20 +0200
  Re: Parallel FIB anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-05-02 14:13 +0000
    Re: Parallel FIB Paul Rubin <no.email@nospam.invalid> - 2013-05-02 08:25 -0700
    Re: Parallel FIB mhx@iae.nl (Marcel Hendrix) - 2013-05-03 07:04 +0200
      Re: Parallel FIB anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-05-03 12:26 +0000
        Re: Parallel FIB Bernd Paysan <bernd.paysan@gmx.de> - 2013-05-03 15:23 +0200
          Re: Parallel FIB fred <email@address.com> - 2013-05-03 16:56 +0100
          Re: Parallel FIB Bernd Paysan <bernd.paysan@gmx.de> - 2013-05-03 18:13 +0200
        Re: Parallel FIB mhx@iae.nl (Marcel Hendrix) - 2013-05-03 21:14 +0200
          Re: Parallel FIB anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-05-04 13:45 +0000
        Re: Parallel FIB mhx@iae.nl (Marcel Hendrix) - 2013-05-03 21:29 +0200
          Re: Parallel FIB mhx@iae.nl (Marcel Hendrix) - 2013-05-03 23:53 +0200
            Re: Parallel FIB Paul Rubin <no.email@nospam.invalid> - 2013-05-03 18:10 -0700
              Re: Parallel FIB mhx@iae.nl (Marcel Hendrix) - 2013-05-04 07:07 +0200
                Re: Parallel FIB mhx@iae.nl (Marcel Hendrix) - 2013-05-06 21:09 +0200
        Re: Parallel FIB albert@spenarnc.xs4all.nl (Albert van der Horst) - 2013-05-04 00:26 +0000

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