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

david at david at
Thu Jul 9 20:54:09 EDT 2009

On Thu, 9 Jul 2009, John Gilmore wrote:

>>                                                         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%
> improvement.
> 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.

part of the question is going to be what modules need to be installed.

a generic fedora system installs modules for everything, but each module 
wastes a partial page of ram, which can add up on a low memory system.

you may want to include every USB driver as a module, or it may be worth 
trimming down the list of modules with a method to add others as needed.

David Lang

> 	John
> 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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