Re: [gentoo-amd64] AMD64 - Firefox, flash, java, mplayer and more....

[Brett Johnson]

>>
>> A useful pointer - thanks. But it seems to assume that we use Athlon XP
>> processors (FLAGS="-O2 -march=athlon-xp -msse2 -pipe
>> -fomit-frame-pointer"). My box has Opterons, so I assume I should
>> substitute "-march=opteron", no?
>>
>> I've found explanations a bit thin on the ground as to what the C arch
>> flag and the chost definition do. It's generally true that an
>> explanation is far better than an instruction if you want to avoid
>> supplementary questions  :-)
>
> An excerpt from
> http://www.gentoo.org/proj/en/base/amd64/technotes/index.xml?part=1&chap=3
> :
>
> "Unlike gcc 3.3, gcc 3.4 requires that you set -march. The most
> conservative (and supported) CFLAGS can be set as show below:
> ...
> CFLAGS="-march=k8 -O2 -pipe"
> ...
>
> Note: -march=k8 equals -march=athlon64 equals -march=opteron."
>
> Here is an excerpt from
> http://www.gentoo.org/proj/en/base/amd64/technotes/index.xml?part=1&chap=4
> :
>
> "Once gcc-3.4 is released, you should be able to use -march=k8 to optimize
> for the amd64, but it's not mentioned in the changelog if this is
> available for 32-bit compilation as well."
>
> So for the 64-bit install, using k8, athlon64 or opteron will produce the
> same binaries. For the 32-bit chroot, you should use athlon_xp as that is
> the most conservative setting for running in 32 bit mode on the k8
> architecture.
>
A slight change to the above. The requirement to use athlon-xp in the
32-bit chroot is not for bit correctness, it is because GCC 3.3 doesnt
support amd64 specific -march setting. GCC 3.4 just recently went stable
for x86, so in theory, after performing the migration to gcc 3.4 in the
32bit chroot, it may be possible to use the k8 setting in 32bit land.


Random Thought:
---------------
You know you're using the computer too much when:
u wake up with keyboard letters stuck to your forehead!!
	-- RedDawn

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