[SciPy-user] 64 bit and 32 bit on Ubuntu

Nathan Bell wnbell@gmail....
Sun Oct 12 14:14:18 CDT 2008


On Sun, Oct 12, 2008 at 2:45 PM, Kurt Smith <kwmsmith@gmail.com> wrote:
>
> for numerical work, specifically under scipy, etc.  I'm not well
> versed in the low-level pros and cons of 64 bit vs 32 bit, esp. as to
> how it affects scipy performance.  Can you enlighten me?  I"m on an
> Intel Core 2 Duo, 3.16 GHz, E8500, 4 GB RAM.  Will using 64 bit yield
> great benefits running scipy/numpy code automatically, or will it
> require fine-tuning on my part?  Will 64 bit yield benefits besides
> having a larger address space (besides the fact that my 4 GB RAM is
> still addressable by 32 bits, anyway)?
>

I wouldn't expect any significant performance difference.  The x86-64
architecture does bring a few improvements such as more registers and
(guaranteed?) SSE2 support, but the benefit of these depends on the
nature of the application.
http://en.wikipedia.org/wiki/X86-64#Architectural_features

Something in the neighborhood of 20% faster for general purpose codes
should be typical.  OTOH I've found that some pure Python code that
makes heavy use of dictionaries runs slower, possibly owing to the
fact that 64-bit pointers reduce the effective CPU cache size.

Also, you wouldn't be able to address *all* 4GB RAM in a 32-bit OS.
Both Windows and Linux reserve some part of the upper addresses for
the OS, so a process will be limited to something less (3GB to 3.5GB
IIRC).

Keep in mind that 64-bit Linux is approximately 2x cooler than 32-bit
Linux, so the choice is easy IMO.

-- 
Nathan Bell wnbell@gmail.com
http://graphics.cs.uiuc.edu/~wnbell/


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