New kernel branch for XO-1 and XO-1.5 development

John Gilmore gnu at
Thu Jul 9 20:35:50 EDT 2009

>                                                         Given that
> we are building the for completely different CPU core, we will need 
> different kernel RPMs to make sure our kernel is optimized for the 
> given machine.

Optimization is one thing; functioning is another.

Fedora *functions* on just about any x86 system you boot it on.  A
Fedora kernel with OLPC's patches should also *function* when you boot
that kernel on any x86.  Including XO-1 and XO-1.5.

I don't know many people who actually recompile their Fedora kernels
and flip all the hundreds of config switches to "optimize" their
kernel for their hardware.  The vast majority just run the stock
kernel, which "optimizes" the human cost of sysadmin, future upgrades,
security patches, etc.

There was a long debate on the Fedora list about desupporting the
586 so the stock distro could be compiled for the 686.  The problem is
that it breaks *function* for a cheezy optimization of way less than 5%

A tiny number of features (e.g. PAE kernels that use more than 3 GB
of DRAM) require a kernel reconfig/recompile; the rest just happen at
runtime.  OLPC's chip and board support should happen at runtime, like
everybody else's.

With regard to optimization, OLPC is in a tighter position than most
Fedora users, particularly on the XO-1 at 256MB of DRAM.  It might be
worth shipping a custom-configured kernel for the XO-1 to save a meg
of RAM (if it actually did save that much).  A better but harder
approach would be to fix the stock kernel so it can discard more
portions of itself that aren't used on the running hardware.


PS: Someone on the kernel list reported that compiling with
-march=atom made his Geode faster than compiling with -march=geode.
The theory that each board's kernel would be faster when recompiled
for Via vs. Geode should be tested.

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