Hi Yannick,

> My problem is that I tried some performance tests
> on that machines. On the same machine (a dual-opteron
> with 2GB from sun) I have some installed in 32 bits
> and a test one installed in 64+32 bits.
>
> And 32 bits programs are slower on the 64+32 than
> on a "native" 32 bits installation.
> As opterons are not supposed to be slower when
> executing 32 bits code, I can't find the reason of that
> performance problem... In addition with a 64 bits
> system we should hope that some system-related
> operation (memory management...) would be faster,
> even for 32 bits programs.
> The performance factor is 1.15 slower on a 32+64
> regards to a pure 32.

This is not what I see at least on my single CPU P4 (things may be
different on a dual Opteron though):

OS      app     root 4.00.08 stress ROOTmarks
==      ==      =============================
64      64      1056.7 1047.9 1059.8
64      32      942.5 945.7 942.5
32      32      945.0 945.0 947.2

I'll do some more of these measurements eventually, with different
applications and also on dual Opterons.

> Anyone has an idea of the reason ?

There's an overhead for 32-bit system calls. The 64-bit kernel
has additional entry points for those, and the input parameters and values
returned have to be converted. x86_64 has hardware instructions tailored
for doing this, but - depending on the application - it may become
significant.

Which kind of programmes did you try? How long do they take to run?

> -> installing 32 bits over 64 bits:
>
> The "magic" way to do it is to use the option
> '--excludepath=XXX' many times. I used a set of
> 'excludepath' in order to prevent installation on each
> directory that is not supposed to get libraries (it
> would have been easier if a '--onlypath=XX' had
> existed).

Works nicely. The excluded files are not only not installed, they're
also not removed when the i386 package is erased. Now all we need is
a way to teach yum how to do this, during installation and updates ;-)

Cheers,
        Stephan

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