On Friday 22 September 2006 07:56, Ian Pratt wrote:
<snip>
>
> The example you give below is a truly bizarre enumeration of CPUs. X86
> does effectively enumerates [nodes][sockets][cores][threads] (in C
> terminology), hence on a hyperthreaded system PCPU 0 and 1 are in the
> same core.
>
<snip>
Not all X86 machines work this way. For Linux, it depends on the order in
which the processors appear in the SRAT table (or MP table?), as I recall,
and I imagine the same is true for Xen. Most system manufacturers write the
BIOS so that the processor ordering is as you describe. That is logical
processors 0 and 1 are both on socket 0, 2 and 3 are on socket 1, etc.
However, we have encountered BIOS's for AMD procesors which this numbering is
done with logical 0 and 1 being core 0 on socket 0 and 1, respectively.
The numbering continues this way, until all sockets have been enumerated,
then (in a 4-socket system), logical processor 4 is core 1 on socket 0, 5 is
core 1 on socket 1, etc. The apparent rationale for this is that IF you
decide to boot the system with only 4 processors, then you get one active
core on each socket.
(Here logical processor number is the number that smp_processor_id() returns.)
<snip>
--
Ray Bryant
AMD Performance Labs Austin, Tx
512-602-0038 (o) 512-507-7807 (c)
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