[Beowulf] Win64 Clusters!!!!!!!!!!!!

Joe Landman landman at scalableinformatics.com
Sun Apr 8 18:44:34 PDT 2007

Hi Jon

Jon Forrest wrote:
> One thing I've noticed about 64-bit computing in general
> is that it's being oversold. The **only** reason

I disagree (with oversold).

> for running in 64-bit mode is if you need the additional
> address space. Indeed, for some apps this is critical and

No.  The extra registers make compiler optimization work better (lower
register pressure).  The flat memory model (doing away with segmented
registers) simplifies addressing, and reduces the work of the processor
for every physical address calculation (no more segment + offset
operations to perform *before* pushing out the address onto the wires).

64 bit provides more registers and a simpler addressing mechanism.  Well
at least the x64 (AMD64, x86_64,...).

> 64-bit computing solves a real problem. For apps that
> don't need the extra address space, the benefits of
> the additional registers in x86-64 are nearly undone
> by the need to move more bits around, so 32-bit
> and 64-bit modes are pretty much a push. When you

I would love to see your data for this.  Please note that I have quite a
bit of data that contradicts this assertion (e.g. directly measured
performance data, wall clock specifically of identical programs
compiled to run in 32 and 64 bit mode on the same physical machine,
running identical input decks).  This is older data, from 2004.  c.f.
but it is still relevant, and specifically, directly addresses the

> add the additional difficulty of getting 64-bit drivers
> and what-not, I don't think it's worth messing with 64-bit
> computing for apps that don't need the address space.

Which OS are you using?  We haven't had 64 bit driver availability
issues since late 2004, for Linux.  For windows this may be different.
For JackRabbit and our Windows 2003 x64 Server tests, we found it very
difficult to find correct 64 bit Windows drivers (from Intel) for a
network card.  We eventually found it, using many google searches, trial
and error, and some lucky guesses.

> One additional way 64-bit computing is being oversold
> is that there aren't now, and maybe never will be, any
> human written program that requires more than 32 bits
> for the instruction segment of the program. It's simply

This is a bold assertion.  Sort of like the "no program will ever use
more than 640k of memory" made by a computing luminary many moons ago.

> too complex for a human, or a group of humans, to write
> this much code. Again, note that this says nothing

landman at dualcore:~> cat hi.f90
        program hi
        print *,"hi"
landman at dualcore:~> pgf90 hi.f90
landman at dualcore:~> ./a.out
landman at dualcore:~> ls -alF a.out
-rwxr-xr-x 1 landman users 2302794 Apr  8 21:38 a.out*

2.3 MB for hi.

> about the data segment of a program. Also, people tell
> me that there are programs that were generated by other
> programs that are larger than 32 bits. I've never seen
> one, but maybe they exist, and that's what I'm talking
> about human written programs.

I am sorry, but I think this may be an artificial strawman.

Joseph Landman, Ph.D
Founder and CEO
Scalable Informatics LLC,
email: landman at scalableinformatics.com
web  : http://www.scalableinformatics.com
phone: +1 734 786 8423
fax  : +1 734 786 8452 or +1 866 888 3112
cell : +1 734 612 4615

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