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Re: i686 ---> i586, i386 ---> i586, x86_64 stays the same



I just want to make sure the release notes are clear on what is
changing...

The Fedora 6 thru 10 release notes say "Fedora __ requires an Intel
Pentium or better processor, and is optimized for Pentium 4 and later
processors."  The same policy goes back with different words to at least
Fedora Core 2.  ("Pentium" being i586, and I gather from Wikipedia that
Pentium 4 = Intel NetBurst = i786?)

So am I correct in assuming that all the i386 packages, including the
i386 kernel, were backwards-compatible with i386 and i486 CPUs, even
though officially these CPUs were not supported in Fedora 2 thru 10?

If so, wouldn't a small number of users who inexplicably still have i386
and i486 chips find that this is the first Fedora release that does not
work for them, or is it simply impossible that there is anyone still
running it on these architectures?  (I don't seen anything below i586 in
the smolt "active hosts" database.)

The benefits listed on the feature page are:

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

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.
<<

Would a polished version of this be appropriate to add to the "What's
New" section of the release notes?

As for the i586/i686 business, is the following an accurate
understanding?
* Users needing compatibility with the i586 instruction set may use the
kernel.i586 package.
* Users with PAE and NX capable CPUs may use the kernel-PAE.i686
package.
* i686 users without PAE and NX capabilities can also use the
kernel.i586 package, which will not impact performance except for
in-order CPUs like Intel's Atom.
* Both the kernel.i586 and kernel-PAE.i686 packages are optimized for
Pentium 4 compatible chips; the architecture designation indicates the
earliest chips with which the build is compatible.

It also sounds like this might be good advice?:

>>
* Anaconda will automatically choose the best kernel for the system.
* If using the "yum upgrade" method (not recommended), you may need to
install the kernel-PAE.i686 package manually if you have a CPU with PAE
and NX capabilities.  To determine this, run the command:
 grep 'flags.* pae' /proc/cpuinfo | grep -wq nx && echo 'kernel-PAE'
If you see "kernel-PAE" in the output, then your CPU does have these
capabilities.
<<

-B.

On Sun, 2009-04-05 at 17:12 -0400, Will Woods wrote:
> If your CPU supports PAE and NX[2] (or you have >4GB RAM), anaconda will
> install kernel-PAE.i686 - otherwise the basic kernel.i586 package will
> be used[3]. 
...
> [1] In-order CPUs (like Intel's Atom) do benefit from CMOV.
> [2] grep 'flags.* pae' /proc/cpuinfo | grep -wq nx && echo 'kernel-PAE'
> [3] F10 and earlier systems with kernel.i686 will get kernel.i586 as an
> upgrade - if your system is PAE capable you might want to install
> kernel-PAE manually, since using PAE+NX *is* a significant performance
> benefit.
> 


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