Re: NaN slowdown with some processors

[Michael Goffioul]

I can't test on a Core 2 CPU, but here are some results on
a P4 (Family 15, Model 4), with various flavours of ATLAS-3.8.1
(octave-devel, Windows XP, VS2008):

ATLAS+SSE3
octave.exe:1>     a=zeros(300,300);tic;b=(1.0+a)*a;toc
Elapsed time is 0.0375998 seconds.
octave.exe:2>     a=zeros(300,300);tic;b=(NaN+a)*a;toc
Elapsed time is 0.138695 seconds.

ATLAS+SSE2
octave.exe:1>     a=zeros(300,300);tic;b=(1.0+a)*a;toc
Elapsed time is 0.059979 seconds.
octave.exe:2>     a=zeros(300,300);tic;b=(NaN+a)*a;toc
Elapsed time is 2.3401 seconds.

ATLAS+SSE1
octave.exe:1>     a=zeros(300,300);tic;b=(1.0+a)*a;toc
Elapsed time is 0.0478508 seconds.
octave.exe:2>     a=zeros(300,300);tic;b=(NaN+a)*a;toc
Elapsed time is 19.1522 seconds.

Reference F77
octave.exe:1>     a=zeros(300,300);tic;b=(1.0+a)*a;toc
Elapsed time is 0.002455 seconds.
octave.exe:2>     a=zeros(300,300);tic;b=(NaN+a)*a;toc
Elapsed time is 0.0332971 seconds.

Michael.


On Wed, Jun 4, 2008 at 8:11 AM, Olli Saarela <address@hidden> 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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