Nothing much. Use like normal x86 besides:
- Kernel set to Your CPU in Processor Setttings (generic x86_64 is good for
all configurations).
- Accept keyword for "Beta"-like packages is ~amd64 not ~x86
- You don't have to set MMX flag, but set SSE, SSE2 and if Your CPU have it
- SSE3 this will optimize floating point operations.
- Enable SMP (symmetric Multiprocessing) where available - by flags.
- If it's multicore (I have Intel on my LAP so don't know about Your CPU)
set MAKEOPTS to cores count+1.
- If it's multicore try to enable threads flag - this boosts performance
even on single core cpus, but on multicore will make much difference.
- Chceck by eselect what profile of portage you have set as default. If is
not try setting some with Amd64 on path.
- When GCC upgrade check if "multilib" is set - this will enable You to link
with 32-bit libs and 64-bit (as standard).
- In kernel set ciphers and algorithms (like MD5, SHA etc) to amd64 version.

I think that's it. Everything elese should be fine.

2010/12/8 Dale <rdalek1967@gmail.com>

> Hi,
>
> First post here.  I'm usually on gentoo user.  I'm in the process of
> building a new system which will be 64 bit.  I am looking for advice.  I
> would like people to post things that I might run into that one wouldn't
> expect and some things that are different from x86.  I was looking at
> something on my old rig and noticed the USE flag smp.  I didn't know about
> that until I ran up on it.  I learned something by pure dumb luck.
>
> I'm a long time Gentoo user.  Installed it at the early stages of 1.4.  I
> also use KDE and have fluxbox installed as a backup.  The processor is a AMD
> Phenom II X4 955 @3.2Ghz.  It will start out with one 4Gb stick of ram.  I
> plan to expand that later.
>
> What are some things that I should watch for and enable that isn't so
> obvious for someone new to 64 bit?
>
> Thanks.
>
> Dale
>
> :-)  :-)
>
>


-- 
Mateusz Mierzwiński

Bluebox Software http://www.blueboxsoft.pl/mateusz-mierzwinski