NaN slowdown with some processors

[David Bateman]

Olli Saarela wrote:
> Hello,
>
> I'm planning to buy a new desktop machine, and since my computations 
> utilize NaN values heavily, I'd like to know whether Intel Core 2 
> processors suffer from the same slowdown with NaN values as Pentium. For 
> details, see http://www.cygnus-software.com/papers/x86andinfinity.html
>
> If someone has Octave on a machine with a Core 2 processor, please run 
> the following commands and tell the results. (Or a more detailed test 
> from ftp://ftp.cygnus-software.com/pub/specialnumbers.zip)
>
>      a=zeros(300,300);tic;b=(1.0+a)*a;toc
>      a=zeros(300,300);tic;b=(NaN+a)*a;toc
>
> Below are results from my current machines. Since SSE2 in Pentium isn't 
> affected with the slowdown, it seems that for some reason the commands 
> above don't utilize SSE2. AMD processors aren't affected.
>
> Pentium M, Octave 3.0.1 MSVC2005 SSE2
>      octave-3.0.1.exe:8> a=zeros(300,300);tic;b=(1.0+a)*a;toc
>      Elapsed time is 0.0430298 seconds.
>      octave-3.0.1.exe:9> a=zeros(300,300);tic;b=(NaN+a)*a;toc
>      Elapsed time is 28.8307 seconds.
>
> Pentium 4 (Family 15, Model 2), Octave 3.0.1 MSVC2005 SSE2
>      octave-3.0.1.exe:2> a=zeros(300,300);tic;b=(1.0+a)*a;toc
>      Elapsed time is 0.0257161 seconds.
>      octave-3.0.1.exe:3> a=zeros(300,300);tic;b=(NaN+a)*a;toc
>      Elapsed time is 15.7125 seconds.
>
> AMD Turion 64 X2, Octave 3.0.1 MSVC2008 SSE3
>      octave-3.0.1.exe:3> a=zeros(300,300);tic;b=(1.0+a)*a;toc
>      Elapsed time is 0.0244939 seconds.
>      octave-3.0.1.exe:4> a=zeros(300,300);tic;b=(NaN+a)*a;toc
>      Elapsed time is 0.0251131 seconds.
>
> Thank you,
>    Olli
>
> _______________________________________________
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> Help-octave at octave.org
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>
>   
With a Core2 Duo 2.2GHz T7500 processor

octave:3> a=zeros(300,300);tic;b=(1.0+a)*a;toc
Elapsed time is 0.00938201 seconds.
octave:4>      a=zeros(300,300);tic;b=(NaN+a)*a;toc
Elapsed time is 0.00932693 seconds.

D.


-- 
David Bateman                                David.Bateman at motorola.com
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