Intel 64 and IA-32 Architectures Software Developers Manual Volume 3A, System Programming Guide, Part 1

Vol. 3A 7-23
MULTIPLE-PROCESSOR MANAGEMENT
multi-threading resource topology in an MP system (See Section 7.10.1,
“Hierarchical Mapping of Shared Resources”). The initial APIC ID may consist of
up to four bit-fields. In a non-clustered MP system, the field consists of up to
three bit fields.
Figure 7-2 shows two examples of APIC ID bit fields in earlier single-core processors.
In single-core Intel Xeon processors, the APIC ID assigned to a logical processor
during power-up and initialization is 8 bits. Bits 2:1 form a 2-bit physical package
identifier (which can also be thought of as a socket identifier). In systems that
configure physical processors in clusters, bits 4:3 form a 2-bit cluster ID. Bit 0 is used
in the Intel Xeon processor MP to identify the two logical processors within the
package (see Section 7.10.2, “Identifying Logical Processors in an MP System”). For
Intel Xeon processors that do not support Intel Hyper-Threading Technology, bit 0 is
always set to 0; for Intel Xeon processors supporting Hyper-Threading Technology,
bit 0 performs the same function as it does for Intel Xeon processor MP.
For more recent multi-core processors, see Section 7.10.1, “Hierarchical Mapping of
Shared Resources” for a complete description of the topological relationships
between logical processors and bit field locations within an initial APIC ID across Intel
64 and IA-32 processor families.
Note the number of bit fields and the width of bit-fields are dependent on processor
and platform hardware capabilities. Software should determine these at runtime.
When initial APIC IDs are assigned to logical processors, the value of APIC ID
assigned to a logical processor will respect the bit-field boundaries corresponding
core, physical package, etc. Additional examples of the bit fields in the initial APIC ID
of multi-threading capable systems are shown in Section 7.10.
Figure 7-2. Interpretation of APIC ID in Early MP Systems
0
Processor ID
17 432
Cluster
Reserved
0
Processor ID
17 4325
Cluster
Reserved
APIC ID Format for Intel Xeon Processors that
APIC ID Format for P6 Family Processors
0
do not Support Hyper-Threading Technology