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Re: Jakub's Recommendations for ia32 Support

On Tuesday, 03 February 2009 at 18:11, Warren Togami wrote:
> I talked with Jakub Jelinek to ask his recommendation of how Fedora 11
> should proceed.
> Jakub recommends i586.rpm for Fedora 11, because it doesn't gain us much
> of anything to go with i686 minimum.  The benefits of i586 to i686 are
> simply not important because cmov is usually not a worthwhile
> optimization on ia32.  You sometimes find some testcase where cmov
> improves something, but often you find one where it pessimizes something
> as well.

I'd like to see a case (not involving Pentium 4) where using cmov is slower
than not using it. It definitely is faster for decoding H.264 in FFmpeg
for example.

>  i686 to i686 w/ SSE2 would be a performance win, but that is
> clearly not an option for Fedora.

SSE2-optimized libraries can be built and installed into /usr/lib/sse2.
Our ld.so already supports that.

> Jakub recommended doing comparison tests of -m32 -march=i586
> -mtune=generic vs. -m32 -march=i686 -mtune=generic with Spec2k and
> Spec2006 benchmark tools.  Anyone interested in trying this?

Are these tools' sources available somewhere? Last I searched I couldn't
find them.

> He also wants gcc-4.4 to go into dist-f11 immediately after Alpha, even
> if we are not doing the mass rebuild just yet.  It is ABI compatible so
> shouldn't cause any problems on its own.  Meanwhile it will allow
> maintainers to fix some problematic packages sooner.


> In related news, cebbert wants to do the following to the F-11 kernel:
> - Eliminate the current i686 kernel.
> - i686 hardware would get i686 PAE by default.

Not all i686 hardware is PAE capable.

> - i586 kernel becomes i686, except without cmov.  This is primarily so
> people don't complain when they realize they have the "i586" kernel.

And this will be installed on anything that's not PAE capable?


Fedora http://fedoraproject.org/wiki/User:Rathann
RPMFusion http://rpmfusion.org | MPlayer http://mplayerhq.hu
"Faith manages."
        -- Delenn to Lennier in Babylon 5:"Confessions and Lamentations"

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