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ShadyMilkman
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PostPosted: Sun Apr 21, 2002 10:48 pm    Post subject: Best -march option? Reply with quote

I don't actually have a computer right now, but I'm getting an Athlon XP 2000+ system from components as soon as it ships. Anyway I'm very interested in getting the most juice out of it, so I figured that optimizations are very important. Is i686 the best option for athlon xp? I've seen on the gcc.gnu.org that there is also a "athlon-xp" option, but does this really help? I know I shouldn't have any troubles with my system being slow, especially w/ 512MB DDR, but still, I'm a perfectionist hehe. Should I save my time and download the stage[2-3] images? Anybody here w/ Athlon XPs? Thanks.
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Utoxin
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PostPosted: Sun Apr 21, 2002 10:55 pm    Post subject: Reply with quote

I'd definately start at stage1. The bootstrap doesn't take /that/ long, and I'm suspicious that it gets 5-10% more performance out of your system. Or maybe that's just Gentoo in general. It feels so... fast.

As far as the -march option, I don't know how much the athlon-xp option helps. But it won't hurt.
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ShadyMilkman
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PostPosted: Sun Apr 21, 2002 11:00 pm    Post subject: Reply with quote

Good point... Anyway thanks for replying so fast (10 min!) I'll definitally go for the full compile, just realized that I have to configure a bunch of kernel stuff too.
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PostPosted: Sun Apr 21, 2002 11:09 pm    Post subject: Re: Best -march option? Reply with quote

Remember that the --march=athlon option is available only for GCC version >= 3.0. But that version won't compile every Gentoo package yet. When using GCC 2 the march-option-question is a non-brainer.

BTW, are there any news from the Gentoo GCC3 frontier?
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Malakin
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PostPosted: Sun Apr 21, 2002 11:32 pm    Post subject: Reply with quote

Since nobody really answered your question.

-march=i686 is best for an athlon on < 3.0 gcc.

Taken from the gentoo faq:

Quote:

When you use any optimizations beyond -O3, you're really taking the risk of having broken packages. Very aggressive optimizations sometimes cause the compiler to streamline the assembly code to the point where it doesn't quite do the same thing anymore. Loc-Dog (on IRC) uses -O3 -mcpu=1686 -march=i686 -fforce-addr -fomit-frame-pointer -funroll-loops -frerun-cse-after-loop -frerun-loop-opt -malign-functions=4, which is about as much as I'd want to push global optimization settings.


I added -ffast-math to mine also post bootstrap and didn't have any problems(athlon xp1800, kt333, 512M ddr 333mhz cas2 t1). If you're using a kt333 you'll need a slightly newer kernel then what gentoo is currently providing as dma won't be supported, It appears to be supported as of 2.4.19-pre6 although I just hacked the gentoo kernel source to get it working.
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ShadyMilkman
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PostPosted: Mon Apr 22, 2002 12:39 am    Post subject: Reply with quote

Sorry I'm obviously not a as much of a linux jedi as you are, so excuse the following questions...
<!-- being newbie questions>
Does Gentoo come w/ gcc>=3.0? Also, do you use i686 then? And are you saying that it's not good to compile the _kernel_ with -ffast-math?

Also, what exactly is kt333? My m/b is an FIC AN11 it's got onboard ATA/100 (RAID) if that's what you're referring to and if that is a problem then should I just try to get a .diff from kernel.org and patch it?
<--! end newbie questions>
Wow that's a lot of questions. Anyway, glad to have such a great user base for gentoo!
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Malakin
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PostPosted: Mon Apr 22, 2002 6:01 am    Post subject: Reply with quote

Gentoo uses GCC 2.95.3

For your march just use i686, don't worry about using anything else. -O3 which is already in make.conf and -march=i686 is fine.

Your FIC AN11 is a kt266a based motherboard. kt266a is the via chipset that the motherboard is based on. The kt266a is fully supported. The kt333 is very new so support for it just made it into the kernel but you're not using it so don't worry about it :)
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ShadyMilkman
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PostPosted: Mon Apr 22, 2002 4:00 pm    Post subject: Thanks! Reply with quote

Thanks so much! Now if only they weren't back ordered on my processor :x

Anyway you guys rock 8)
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mmuser
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PostPosted: Mon Apr 22, 2002 4:27 pm    Post subject: best optimizations Reply with quote

Also in the FAQ it states

"
I'm finding things to be really unstable and I'm using "-O9 -ffast-math -fomit-frame-pointer" optimizations. What gives?

When you use any optimizations beyond -O3, you're really taking the risk of having broken packages. Very aggressive optimizations sometimes cause the compiler to streamline the assembly code to the point where it doesn't quite do the same thing anymore. Loc-Dog (on IRC) uses -O3 -mcpu=1686 -march=i686 -fforce-addr -fomit-frame-pointer -funroll-loops -frerun-cse-after-loop -frerun-loop-opt -malign-functions=4, which is about as much as I'd want to push global optimization settings. Beyond this, it's best to use ultra-high optimizations only with specific packages where you really need that extra 2%, and where you can easily test the package to ensure that it hasn't been optimized into oblivion.
"

Just a little extra opt!
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