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Date:      Sat, 23 Jan 2010 00:54:58 +0100
From:      Ivan Voras <ivoras@freebsd.org>
To:        freebsd-questions@freebsd.org
Subject:   Re: FreeBSD 8.0 amd64 on Nehelem Xeon?
Message-ID:  <hjddsk$8k9$1@ger.gmane.org>
In-Reply-To: <560f92641001221524n1290e70fi51d766e8e0f488bf@mail.gmail.com>
References:  <560f92641001221524n1290e70fi51d766e8e0f488bf@mail.gmail.com>

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Nerius Landys wrote:
> I'm in the process of purchasing a small Nehelem-based server (Xeon
> L5506 CPU to be exact).  I will be installing some flavor of FreeBSD
> 8.0 (either i386 32 bit or amd64 64 bit, to be exact).  I have no
> immediate need for a 64 bit server, as none of the processes that I
> will be running in the forseeable future will require more than 3 gigs
> of memory.  My primary use for the server (which will be in a data
> center) will be to run video games servers; the exact game I'll be
> running is based on the ioquake3 open source engine, which compiles
> and runs fine on FreeBSD, at least 32 bit (have not tried 64 bit
> FreeBSD yet, but will get around to that).
> 
> My two concerns when making a decision between 32 bit and 64 bit are:
> 
> 1. Performance.  Will there be any difference in performance between a
> 64 bit OS and 32 bit on my Nehelem?

Probably not so much that you would notice (i.e. not something the users 
would immediately feel) - for general loads we're talking about low 
percentages in either direction.

But installing a 64-bit OS is more like planning for the future. Maybe 
you will need more RAM for some application and then you will be stuck 
with a 32-bit OS.

> 2. Availability of software.  Will some software run only on 32 bit?
> Only on 64 bit?

There probably are some. If you are only interested in FreeBSD ports, 
you can make a list of which ports you need and then inspect their 
Makefiles to see if there's a flag disabling them on the amd64 architecture.

Another option is that you bring up a 32-bit-only jail and run your 
32-bit applications from it.

Additional information for Nehalems is that you should stick to the more 
widely available models - the 4 core+HTT ones. Some of the more exotic 
ones (6 core) might have problems with ULE and topology guesswork.

http://suckit.blog.hu/2009/10/05/freebsd_8_is_it_worth_to_upgrade




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