Re: x86_64: apic id lift patch

[Andi Kleen]

On Mon, Nov 21, 2005 at 02:17:35PM -0800, yhlu wrote:
> > Can you please explain clearly:
> >
> > - What are you changing.
> 1.  use core_vir instead of x86_max_cores, for E0 later single core,
> core_vir could be 2, and x86_max_cores still is 1. So it makes node
> calculation right.

max_cores should be 2 here.

> > - What was the problem with the old behaviour
> 1. for E0 single core, node 2, initial apicid is 4, and old cold will
> get node=4 instead of 2.
> 2. if the lifted apicid is not continous, it will assign strange node
> id to the cpu.

Is there a good reason in the BIOS to not make it contiguous?

> > - Why that particular change
> 1. We can get exact node id and core id from initial apicid for E0 later.
> > - Why can't that APIC number setup not be done by the BIOS itself
> 1. That patch the code more generic. and don't assume the lifted
> apicid is continous.

It's only the last resort fallback anyways. I would prefer to not
make it more complicated. The recommend way is you supplying
a SRAT table, then you're independent of any such fallback heuristics
and just tell the kernel the right mapping.

-Andi
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