Logical CPU -> physical CPU conversion

Petri Helenius pete at he.iki.fi
Thu Feb 17 07:26:38 PST 2005

John Baldwin wrote:

> On Feb 17, 2005, at 3:27 AM, Joseph Koshy wrote:
> For current Intel HTT CPUs, yes.  Note that this might get tricky with
> the dual core CPUs coming from both AMD and Intel in the not too
> distant future as we don't know yet how they will enumerate the cores.
> It may be that the cores "look" like HTT cores when they are actually
> full cores, so I would try to abstract this in a way that you can use
> different implementations for different CPUs to determine when a
> logical CPU is a HTT CPU vs. a full core.  Also, I imagine that even
> with dual core Intel CPUs there is a chance that they might do HTT
> inside each core, so that a single physical processor would have 2
> cores each with 2 HTT so a total of 4 logical CPUs from one piece of
> silicon.
It would be logical to follow the documented convention;
In future IA-32 processors supporting Hyper-Threading Technology that 
implement more than
two logical processors per physical processor, the logical processor bit 
shown in Figure 7-5 will
be expanded to a 2- or 3-bit field to allow each of the logical 
processors to be identified. The
package ID and cluster ID fields will be shifted to the left 
accordingly. Also, the package ID may
be expanded to more than 2 bits, requiring the cluster ID field to be 
shifted to the left.


More information about the freebsd-smp mailing list