Large mmio resources and 4G+ of RAM...

Stefan Reinauer stepan at
Tue Jun 1 03:11:00 CEST 2004

* Eric W. Biederman <ebiederman at> [040601 09:53]:
> Essentially.  Although the pci devices don't vanish you likely can't use
> them because some of their BARS have values that 32bit kernels can't
> cope with.  lspci should let you see that though.   A 32bit kernel
> with PAE enabled could code but no one has written the code.
Are there any drawbacks to that solution? This should be addressed to
the Linux kernel developers. Given the advantages this brings, this
would probably something people would like to see.

> I don't have a problem with adding an option to disable this for 32bit
> kernels.  I am just tired of optimizing 64bit machines for 32bit
> kernels.
The silver bullet would be an option in the cmos option table to trigger
the one or the other behaviour. Or maybe it is enough to just put the
PCI BARs into 32bit address space whenever it fits there, taking the
amount of RAM into regard.
I agree it does not make sense to _optimize_ for 32bit kernels.
Essentially there are two groups of potential LinuxBIOS users in this
case: Those with small amounts of RAM (ie amd64 based embedded
solutions) might use 32bit code because it's easy to test it on many
PCs. Those with large amounts of RAM don't want to use a 32bit kernel
anyways. With more than about 1G of RAM 32bit Linux performance breaks
down noticably compared to the 64bit variant.


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