On Fri, 23 Mar 2007, Brett Viren wrote:

> Johan Mares <[log in to unmask]> writes:
>
>> If you have dual core 64 bits processors in your server. Is it
>> recommended to install x86-64 version of a linux distro like SL ?
>> What are the benefits ? Are there any disadvantages ? It would be for
>> a LAMP, so would Apache or MySQL perform better or wouldn't they make
>> no use of it ?
>> Does anyone have any experience with this ?
>
> 32 bits: more software available, typically proprietary in nature.

Which often runs just as fine under the 64bit OS.

> Can access only <4GB RAM.

That's a common misconception. There's a per-process limit of 3 GB with 
the standard kernel. But the system can have and use more memory. Even 
32-bit SL3 can handle at least 16GB with the ordinary -smp kernel.

> 64 bits: ~20% faster floating point (AMD only I believe), can access

Typically 20% faster for many scientific applications, with few 
exceptions. A bit more than 20% with AMD CPUs. Not limited to floating 
point processing.

IIRC, MySQL is one of those that do benefit but not that much. OpenSSL may 
be anything from slightly slower to much much (several times!) faster, 
depending on cipher and task. No clue how apache behaves.

3GB per-process address space limit for 32-bit apps on SL3, 4GB on SL4.
No (serious) such limit for 64-bit apps.

> more RAM than you can afford.  Potential compilation problems of
> legacy code.

Usually, serious compilation and runtime problems of bad code, legacy or 
not.

Larger memory footprint, depending on application and payload.


The last two probably don't apply to a LAMP. I'd personally go for x86-64.


Regards,
 	Stephan

-- 
Stephan Wiesand
   DESY - DV -
   Platanenallee 6
   15738 Zeuthen, Germany