Jakub's Recommendations for ia32 Support

[Josh Boyer]

On Wed, Feb 04, 2009 at 01:56:16AM +0100, Dominik 'Rathann' Mierzejewski wrote:
>On Wednesday, 04 February 2009 at 01:34, Callum Lerwick wrote:
>> On Tue, 2009-02-03 at 19:53 +0100, Dominik 'Rathann' Mierzejewski wrote:
>> > >  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.
>> 
>> Why does SSE2 get this treatment, and not SSE? I've found SSE much more
>> useful, and more common. SSE2 pretty much means P4 only on i386, Athlons
>> didn't get SSE2 until the Athlon 64 and those should be running x86-64
>> anyway. Whereas there's a lot of Pentium 3s and Athlon XPs with SSE out
>> there.
>
>I was wondering about the same thing. There's little to no documentation
>on this subject so I had to dig into glibc sources to see how it works.
>Apparently, glibc distinguishes some "features" for CPUs and those that
>are "major" can have separate directories with optimized libraries.
>In Fedora, "major" features are "i686" and "sse2". Whereas in Debian,
>it's just "cmov", apparently.
>
>Can anyone shed more light here? Jakub?

It extends to other architectures as well, fwiw.  On PowerPC, you can
have optimized libraries for ppc970,power4,power5,power6, and cell I
believe.  For Fedora, optimized libraries are built for power6/power6x.

josh