Features/F12X86Support

= Fedora 12 x86 Support =

Summary
With Fedora 11, we moved the base architecture to i586. With Fedora 12, we are changing the base architecture to i686, and optimizing for current 32-bit processors.

Owner

 * Name: Bill Nottingham


 * email: notting@redhat.com

Current status

 * Targeted release:
 * Last updated: 2009-08-20
 * Percentage of completion: 100%

Detailed Description
Fedora 11 has i586 as the base 32-bit x86 architecture.

For Fedora 12, we will switch to i686 as the base architecture (including CMOV), and optimize for Atom processors.

This means we will lose support for the following CPU families:
 * Intel i586 (all)
 * National Semiconductor Geode processors
 * VIA C3 (Ezra and Samuel Cores)
 * AMD Geode GX

AMD Geode LX (as used in the OLPC XO laptop) and later Geode NX processors should still work. Those interested are, of course, welcome to set up a secondary arch for older processors.

Benefit to Fedora

 * Faster binaries on mainstream architectures (Pentium M, Via C7, all 64-bit arches, Atom)
 * Realistically, we don't support i586 as a practical matter. Enforce that more logically.
 * Fewer kernel builds

Scope

 * The default 32-bit x86 target in koji would be changed from i586 to i686 - DONE
 * The kernel would build a kernel and kernel-PAE package for i686 - DONE
 * The glibc package would be modified such that i686 builds would produce 'normal' package sets - DONE
 * The openssl package would be modified such that i686 builds would produce 'normal' package sets - DONE
 * The default compiler flags for gcc in redhat-rpm-config would be changed as follows: - DONE
 * i386: -march=i686 -mtune=atom
 * mock would be modified so it defaults to i686 builds for F-12 and later - patch posted
 * A mass rebuild would need to be done for the RPM architecture changes and the compiler flag changes - DONE

How To Test
Ensure that all packages are built for i686.

Additional testing could benchmark apps to see any difference in code size and app speed.

User Experience
The 32-bit x86 distro should be faster; basic benchmarks show at least a 1% improvement in generic code, even without autovectorization.

Dependencies

 * gcc and redhat-rpm-config would need changed for the default compiler flags
 * koji configuration would need a tweak for the default architecture
 * the kernel would need to change its package output

Contingency Plan
If necessary, we can revert to providing i586 binaries. However, once we start a mass rebuild, this would require another mass rebuild to undo.

Documentation
There should not be any required.

Release Notes
A restating of the 'detailed description' above should be sufficient.

Comments and Discussion

 * See Talk:Features/F12X86Support