Thread by @vagnerpilar

Packages sets and #SMT sets. Windows uses 5 fields in the KPRCB to determine correct scheduling decisions when dealing with logical processor topologies. The first field, #CoresPerPhysicalProcessor, determines wheter this logical processor is part of a multicore package. /1

It's computed from the CPUID returned by the processor and rounded to a power of 2. The 2nd field, #LogicalProcessorPerCore, determines wheter the logical processor is part of an SMT set, such as on an AMD with SMT, it is also queried through CPUID and rounded. /2

Multiplying these 2 numbers yields the number of logical processor per package, or an actual physical processor that fits into a socket. /3

With these numbers, each PRCB can then populate its #PackageProcessorSet value This is the affinity mask describing which other logical processors whitin this group (because packages are constrained to a group) belong to the same physical processor. /4

Similarly, CoreProcessorSet value connects other logical processors to the same core, also called an SMT set. Finally, #GroupSetMember value defines which bitmask within the processor group identifies this very logical processor. /5

For example, the logical processor 3 normally has a GroupSetMember value of 8 (which equals 2 to the third power). /6

!smt #WinDBG