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

Vol. 3A 7-41
MULTIPLE-PROCESSOR MANAGEMENT
if (vendor string EQ GenuineIntel) {
return (feature_flag_edx & HWMT_BIT); // bit 28
}
return 0;
}
2. Find the Max number of logical processors per physical processor package.
#define NUM_LOGICAL_BITS 0x00FF0000
// Use the mask above and CPUID.1.EBX[23:16] to obtain the max number of logical processors
// per package,
//Returns the max number of logical processors per physical processor package;
// the actual number of logical processors per package enabled by OS may be less.
// Software should not assume the value a power of 2.
unsigned char MaxLPPerPackage(void)
{
if (!HWMTSupported()) return 1;
execute cpuid with eax = 1
store returned value of ebx
return (unsigned char) ((reg_ebx & NUM_LOGICAL_BITS) >> 16);
}
3. Find the max number of processor cores per physical processor package.
// Returns the max number of processor cores per physical processor package;
// the actual number of processor cores per package that are enabled may be less.
// Software should not assume cpuid reports the value of
// “maximum number of cores per physical processor” must be power of 2.
unsigned MaxCoresPerPackage(void)
{
if (!HWMTSupported()) return (unsigned char) 1;
if cpuid supports leaf number 4
{ // we can retrieve multi-core topology info using leaf 4
execute cpuid with eax = 4, ecx = 0
store returned value of eax
return (unsigned ) ((reg_eax >> 26) +1);
}
else // must be a single-core processor
return 1;
}