Re: State of the Linux PCI and PCI Hotplug Subsystems for 2.6.16-rc5

[Linus Torvalds <torvalds@osdl.org>]

On Thu, 9 Mar 2006, Tomasz Torcz wrote:
> > 
> >   "Fedora rawhide kernel stopped booting for a bunch of people, all with 
> >    686-SMP boxes. I saw it myself too, it hung just after the 'write 
> >    protecting kernel rodata'.
> > 
> 
>   Ubuntu has similar problem:
> https://launchpad.net/distros/ubuntu/+source/linux-source-2.6.15/+bug/29601
>  I believe Ubuntu's 2.6.15 source is vanilla+git patches.

Interesting. He also apparently boots with "noapic nolapic" on the "386" 
kernel, but not the "686" kernel. I wonder what the differences in Kubuntu 
kernels are between 386/686 kernels. Is it _just_ the CPU type? If so, the 
largest difference is probably just compiler instruction usage/scheduling.

Ben?

Also, the 686 one apparently boots with "acpi=off" or "pci=noacpi" 
(although then some interrupts don't work, which I guess shouldn't be a 
huge surprise). I do wonder if maybe we have a miscompile issue.

There are a few (but really not very many) other differences between M386 
and M686 kernels too. Notably CMPXCHG/XADD isn't used unconditionally on 
the M386 kernel. That impacts the new mutex code (it adds a few 
conditional jumps, but still ends up using XADD since the CPU actually 
supports it).

		Linus
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