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SubjectRe: RFC: /proc/cpuinfo confusion with AMD processors
On Mon, Jun 30, 2014 at 08:50:47AM -0400, Prarit Bhargava wrote:
> AMD defines a "Package" as the hardware processor itself. Each Package contains
> multiple Nodes, and each Node has multiple Compute Units. Each Compute Unit can
> have up to 2 cores that [with the 62xx and 63xx] do not have multiple Threads.
>
> That is, to determine the number of CPUs that Linux sees, multiply
>
> Package * Nodes * Compute Units * Cores
>
> Note that Nodes and Compute Units are not indicated in /proc/cpuinfo directly
> (although it could be argued that they should be).
>
> The output of /proc/cpuinfo is confusing at this point as ...
>
>
> processor : 31
> vendor_id : AuthenticAMD
> cpu family : 21
> model : 2
> model name : AMD Opteron(tm) Processor 6386 SE
> stepping : 0
> microcode : 0x6000822
> cpu MHz : 2800.000
> cache size : 2048 KB
> physical id : 1
> siblings : 16 <<< this is number of threads per package
> core id : 7 <<< this is the core id of this thread relative to node
> cpu cores : 8 <<< this is the number of cores per node

siblings / cpu cores = threads per compute unit.

> which makes deciphering the system topology quite difficult as values are
> relative to both nodes and the entire package. It is not possible using this
> information to uniquely identify a processor.

To do what with that information? What is the task you're trying to
accomplish?

> Thoughts/concerns?

BIOS does all kinds of hacks and renumbering to accomodate the
brainf*cked design of other OSes so this info you're trying to put in
cpuinfo might turn to be completely misleading utterly useless in some
cases.

--
Regards/Gruss,
Boris.

Sent from a fat crate under my desk. Formatting is fine.
--


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