Changing the default 32-bit x86 arch for Fedora 12 (#2)

[Chris Adams]

Once upon a time, Bill Nottingham <notting at redhat.com> said:
> Why?
> 
> - We don't really support i586 in any meaningful matter

What does this mean?  Does Fedora not run on i586?  Why was there a
mass-rebuild for i586 if it doesn't work?

> - We are likely doing a mass rebuild for F-12 anyways, might as well switch
>   while we're doing it

That's a pretty poor justification.

> - Atom is the only currently produced 32-bit x86 chip of note; optimize
>   for what's currently available

There are also lots of other chips that people run 32 bit x86 code on.
I don't think Atom is a majority percentage of 32 bix x86 Fedora users
either.

> If you want numbers, I did some benchmarking of code [1] with various
> build options on a variety of processors, with the F-11 gcc code. All
> of these results are relative to a F-11 baseline of "-march=i586
> -mtune=generic".
> 
> 		P4 2.4Ghz	Athlon 3400+	Core2Duo E6850	Atom N270
> march=i686/	-1.1%		+2.0%		+0.9%		+0.6%
>  mtune=generic
> march=i586/	+0.3%		-0.3%		-0.2%		+1.3%
>  mtune=atom
> march=i686/	-1.5%		+1.2%		+0.5%		+1.7%
>  mtune=atom
> 
> Bill
> 
> [1] gzip, bzip2, math simulation, mp3 encode/decode, ogg encode/decode

Okay, before I thought you said this was a "1-2% improvement across the
board", but now it is a 1% improvement on some CPU-intensive operations
on some CPUs (and a 1% performance hit on other CPUs).

How does this affect multilib on x86_64?

The justification for the i586 rebuild was that there hasn't been a
Fedora i386 kernel for years (so i586 was already required anyway).
This is the first time Fedora is proposing to throw out CPU support in a
long long time, and I find a minimal improvement on some targeted
benchmarks a poor justification.

It would seem to me that adding a few targeted Atom packages would be a
better use of resources (e.g. similar to openssl.i686).

-- 
Chris Adams <cmadams at hiwaay.net>
Systems and Network Administrator - HiWAAY Internet Services
I don't speak for anybody but myself - that's enough trouble.