Features/ArchitectureSupport

ArchitectureSupport

Summary

Change what architectures Fedora supports, and what Fedora provides on those architectures.

Owner

• Name: Bill Nottingham
• Name: Jakub Jelinek
• Name: Kyle McMartin

• email: notting@redhat.com, jakub@redhat.com, kmcmartin@redhat.com

Current status

• Targeted release: Fedora 11
• Last updated: 2009-01-28
• Percentage of completion: 0%

Detailed Description

For Fedora 11, we'd like to revisit what architectures Fedora supports, and change some of our defaults so that we work better on those architectures.

The main user-visible changes would be:

• 32-bit x86 would be built for i586 by default.
• The x86_64 kernel would be installed on compatible hardware, even when installing a 32-bit OS
• The PAE kernel would be installed on other 32-bit hardware, where it is supported

The 32-bit LiveCD would remain using a 32-bit kernel, in all likelyhood.

Benefit to Fedora

By optimizing better for the architectures which we support, we give better performance to our users.

By using the x86_64 kernel where appropriate, we allow the kernel to perform better and handle memory better.

By using the PAE kernel where appropriate, we allow features like ExecShield to be used.

By changing the minimum kernel for glibc, we allow the removal of various hacks, tests, and workarounds in the glibc code.

Scope

• The default 32-bit x86 target in koji would be changed from i386 to i586
• mash and pungi would be changed to ship the x86_64 kernel on 32-bit x86
• yum and anaconda would need changes to select the proper kernel
• anaconda will need an override to install the 32-bit kernel on x86_64 hardware, if for no other reason than to be able to test the 32-bit kernel
• syslinux/isolinux may need changes to boot the proper kernel for the installer
• The default compiler flags for gcc in redhat-rpm-config would be changed as follows:
  • i386: -march=i586 -mtune=generic
  • s390x: -march=z9-109 -mtune=z10
• The required kernel for glibc would be changed to 2.6.18
• binutils for ix86 would be compiled to support x86_64 output
• The compiler would be modifed in some way so that x86_64 output would be available on a 32-bit install, in case kernel modules are needed to be rebuilt
• A mass rebuild would need to be done for the RPM architecture changes and the compiler flag changes

How To Test

Install 32-bit Fedora on x86_64 hardware. Make sure the x86_64 kernel is installed.

Install 32-bit Fedora on PAE-supporting 32-bit hardware (in other words: Pentium II/III/4, or Atom.) Make sure the PAE kernel is the default.

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

User Experience

Users of x86_64 hardware should notice a better experience in that they are running a kernel that no longer has to worry about low memory, high memory, etc.

Users of the x86 distribution should notice slight speed improvements.

Dependencies

No external dependencies outside the changes listed in Scope.

Contingency Plan

For compiler flags and default RPM architecture: if we need to change after the mass rebuild, we'd need another mass rebuild.

For x86_64-on-32: do not ship x86_64 on 32-bit x86, only ship 32-bit kernels.

For PAE-on-32: default to the normal i686 kernel, with PAE an option.

Documentation

None specifically.

Release Notes

In Fedora 11, the following changes have been made to architecture support:

• By default, the x86_64 kernel will be installed and used on compatible hardware, even when installing a 32-bit operating system
• By default, the PAE kernel will be used on 32-bit hardware, where appropriate

Comments and Discussion

• See Talk:Features/ArchitectureSupport

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