Re: finding out the boot cpu number from userspace

[Martin J. Bligh]

> ==> Regarding Re: finding out the boot cpu number from userspace; "Martin J. Bligh" <mbligh@xxxxxxxxxxx> adds:
> 
>>> assuming cpu 0 is the boot cpu sounds fragile/incorrect, but for
>>> irqbalanced I'd like to find out which cpu is the boot cpu, is there a
>>> good way of doing so ?
>>> 
>>> The reason for needing this is that some firmware only likes running on
>>> the boot cpu so I need to bind firmware-related irq's to that cpu
>>> ideally.
> 
> mbligh> On any sane arch, cpu 0 *IS* always the boot CPU, as we dynamically
> mbligh> number CPUs that way ... that doesn't mean that it's apicid 0. I
> mbligh> believe that PPC64 screwed this up, but AFAIK, everyone else gets
> mbligh> it correct ... ;-)
> 
> Hmm, do we need to do any special handling for this in the kexec case?
> ISTR having some issues with this when using bootimg years back.

Eric went to some lengths to migrate us back to the original boot CPU 
before kexec'ing. I think this is unnecessary - the new kernel should
handle booting on any CPU just fine (there was a panic in there at one
point if the boot CPU didn't match the BIOS's spec'ed one, but I removed
it).

M.

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