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Re: Changing the default 32-bit x86 arch for Fedora 12



On Mon, Jun 15, 2009 at 01:53:13PM -0400, Bill Nottingham wrote:
 > Way back when in February [1], FESCo decided that for Fedora 11, i586 would
 > be the default architecture, and for Fedora 12, it would be some variant of
 > i686. It's time to follow through on that action item.
 > 
 > I've submitted https://fedoraproject.org/wiki/Features/F12X86Support. It
 > defines the default arch as i686 + SSE2.
 > 
 > Why?
 > 
 > - Faster and more consistent FP math by using SSE2 registers
 > - Allows for autovectorization by GCC where necessary
 > - More clearly delineates our support set of targets, sticking true
 >   to forwards innovation, not necessarily legacy support
 > 
 > What CPUs do we lose that F11 supports?
 > 
 > - Intel i586 (all)

judging by the number of 586 users who register with smolt (less than 0.1%
our entire userbase), not that big a deal.

 > - Intel Pentium Pro
 > - Intel Pentium II
 > - Intel Pentium III
 > - 32-bit AMD Athlon

These are more of a concern. It's difficult to tell from smolt just
how big a deal these are.  P3 & Athlon especially.
I poked Mike privately in the hope that we're gathering enough of
/proc/cpuinfo that we can perhaps get some info on how much our
userbase we'd be shutting off.

I still have two machines that would be affected 
(one in actual production use as a backup server, the other just a
testbox which is tbh rarely powered on) and I'm not even a
good representation of our userbase (I ditched all my ancient junk
a while back).

 > - VIA C3

Some of the later C3's have SSE2, so wouldn't be affected.

 > - AMD Geode
 > - Transmeta Crusoe 

Running the shiny latest bits on these CPUs means you're already
used to living with pain, so a secondary arch seems like the
way forward.

 > Does this lose the PAE/non-PAE kernel split?
 > 
 > - Alas, no.
 > 
 > Will a Fedora rebuilt in this manner work on ...
 > 
 > - OLPC 1.0? No.
 > - OLPC 1.5? Yes.
 > - Atom? Yes.
 > 
 > A seconday arch could be done for these older CPUs, if someone is interested
 > enough. 
 > 
 > Comments? Flames? Predictions of doom?

If we 2nd-arch these, I'm wondering if we should still do the kernel builds
from the main package.  If it's a significant number of users, we're going
to end up with the bug reports anyway so it might as well be something we
know we built etc..

	Dave


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