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8-56 Vol. 3
MULTIPLE-PROCESSOR MANAGEMENT
Example 8-18. Support Routines for Detecting Hardware Multi-Threading and Identifying the
Relationships Between Package, Core and Logical Processors
1. Detect support for Hardware Multi-Threading Support in a processor.
// Returns a non-zero value if CPUID reports the presence of hardware multi-threading
// support in the physical package where the current logical processor is located.
// This does not guarantee BIOS or OS will enable all logical processors in the physical
// package and make them available to applications.
// Returns zero if hardware multi-threading is not present.
#define HWMT_BIT 0x10000000
unsigned int HWMTSupported(void)
{
// ensure cpuid instruction is supported
execute cpuid with eax = 0 to get vendor string
execute cpuid with eax = 1 to get feature flag and signature
// Check to see if this a Genuine Intel Processor
if (vendor string EQ GenuineIntel) {
return (feature_flag_edx & HWMT_BIT); // bit 28
}
return 0;
}
Example 8-19. Support Routines for Identifying Package, Core and Logical Processors from
32-bit x2APIC ID
a. Derive the extraction bitmask for logical processors in a processor core and
associated mask offset for different cores.
int DeriveSMT_Mask_Offsets (void)
{
if (!HWMTSupported()) return -1;
execute cpuid with eax = 11, ECX = 0;
If (returned level type encoding in ECX[15:8] does not match SMT) return -1;
Mask_SMT_shift = EAX[4:0]; // # bits shift right of APIC ID to distinguish different cores
SMT_MASK = ~( (-1) << Mask_SMT_shift); // shift left to derive extraction bitmask for SMT_ID
return 0;
}
b. Derive the extraction bitmask for processor cores in a physical processor package
and associated mask offset for different packages.