Re: Impossible

["Adam C. Powell, IV" <adam powell nist gov>]

Mark Dohojda wrote:

> Hello everyone
>
> I have an Impassable situation here (or so I believe).  I have a
> customer here who just installed Linux on alpha LX600mhz, 512mb of RAM.
> He run C program in NT and in Linux (on the same box), and NT proved to
> be 30% faster.  Now I don't know much about the code, however I know
> that he used the same sources on both of the operating systems.  Also
> the source (to the best of my knowledge) was in no way optimized for NT.
>
> My question is, how can NT beat Linux????? Is that possible? And what to
> do, to make sure that Linux is not going to look bad.
>
> He has RedHat 5.1 no special editions or patches other then the man
> pages patch.

What kind of program is it?  If it has a lot of math it might be sped up
quite a bit using the free fast math library libffm of Wesner and Goto at
http://people.frankfurt.netsurf.de/Joachim.Wesner/ .  A friend of mine had
a program which was heavy in exp and sqrt, and this library sped up its
runtime from 380 seconds to 98!!  That's an extreme example, but just shows
it can make a substantial difference.

One tip- if that library causes floating exceptions even with -mieee (due
to underflow in exp), try removing exp from libffm, building libfm, and
linking -lffm -lfm -lm.  (I had to do this for my friend's program in the
above example.)

Zeen,

-Adam `Cold Fusion' Powell, IV _/\_ http://www.ctcms.nist.gov/~powell/
Call with Netscape Conference!  \/  http://dls.netscape.com/      ____
USDoC, National Institute of Standards & Technology (NIST)  |\ ||<  |
Center for Theoretical and Computational Materials Science  | \||_> |