Re: [POLL] To continue 64 or not?
On Sat, Sep 02, 2006 at 12:38:45AM +0200, tomek.fizyk@op.pl wrote:
> U?ytkownik edwardsa <edwardsa@afrl.kirtland.af.mil> napisa?:
> >I have a question about your claim of performance degradation. See below.
>
> > ...
>
> >Is this degradation true for all applications? To be clear, are you
> >saying that if
> >I compile a fortran code using either pgi, or the 64-bit libraries of
> >g77, that it will run more slowly on a 32-bit compatible distro than it
> >will on a pure-64 bit Debian?
> >If so, why?
>
> I wrote: "...as someone mentioned here some time ago, this 32bit
> compatiblity makes them slower than pure 64bit debian..."
>
> But it turned out that no one mentioned it here (on the list) - I searched
> the list archive and havent found the info and have just remembered that
> I read it here:
> https://alioth.debian.org/docman/view.php/30192/21/debian-amd64-howto.html#id272321
>
> Quote:
> "...While architectures like sparc64 or powerpc64, which provide lib for
> default 32bit libraries and lib64 for extra 64bit libraries, default to
> executing 32bit applications, amd64 defaults to 64bit binaries because of
> the performance benefits it offers in 64bit mode..."
>
> So I don't know exactly what are the benefits, but am beliving what was
> written on the above given site. And I don't know why there is a
> performance degradation.
I think they are referring to comparison between 32- and 64-bit
applications. If the word size were half, then data is moved more slowly
from memory. Also, 64-bit may have a much richer set of machine
instructions so that a given operation can take one clock cycle in
64-bit mode where it might take multiple cycles in 32-bit.
If I'm right, then I don't think that there would be any degradation on
a distro with mixed 32/64 bit libraries, compared to debian's preference
for a chroot. It's more a question of organization.
Art Edwards
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