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SubjectRe: num_possible_cpus() giving more than possible.
Steven Rostedt wrote:
> Hi Mike,
>
> Peter told me that I should report this to you. I have two socket
> single core hyper threaded box (must be hell). Peter told me that the
> num_possible_cpus() should return the number possible on this box. The
> explanation of my box tells us it should be 4. But it in fact returns 8.

It looks like the APIC discovery code is finding 2 dual cores w/HT. I'm
no expert in how all this works but it's assigning

proc 0/2 --> phys id 0 w/2 HT
proc 1/3 --> phys id 3 w/2 HT

Either the BIOS on your machine is confusing the APIC code, the APIC code
has a bug, or you've found an Easter egg... ;-)

>
> nr_cpu_ids also returns 8.

Yes, this reflects the number of possible cpus if all were enabled. On
our systems, we can designate a number of cores to be "present" but
"disabled". Perhaps a "low bin" cpu is basically a dual core with the
non-working core disabled, but still accounted for in the BIOS APIC
tables?

Cheers,
Mike
>
> here's the /proc/cpuinfo:
>
> processor : 0
.
> physical id : 0
> siblings : 2
> core id : 0
> cpu cores : 1
> apicid : 0
> initial apicid : 0
.
>
> processor : 1
.
> physical id : 3
> siblings : 2
> core id : 0
> cpu cores : 1
> apicid : 6
> initial apicid : 6
.
>
> processor : 2
.
> physical id : 0
> siblings : 2
> core id : 0
> cpu cores : 1
> apicid : 1
> initial apicid : 1
.
>
> processor : 3
.
> physical id : 3
> siblings : 2
> core id : 0
> cpu cores : 1
> apicid : 7
> initial apicid : 7
.
> Perhaps since my physical ids show 0 and 3, it thinks it can also have
> a 1 and 2?
>
> Thanks,
>
> -- Steve
>
>



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