Intel ARCHITECTURE IA-32 User Manual download pdf (Page 307)

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101

Vol. 3A 7-39

MULTIPLE-PROCESSOR MANAGEMENT

unsigned int HWMTSupported(void)

{

try { // verify cpuid instruction is supported

execute cpuid with eax = 0 to get vendor string

execute cpuid with eax = 1 to get feature flag and signature

}

except (EXCEPTION_EXECUTE_HANDLER) {

return 0 ; // CPUID is not supported; So HW Multi-threading capability is not present

}

// Check to see if this a Genuine Intel Processor

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

// EBX[23:16] indicates 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 of (cpuid.1.ebx[23:16]) must be 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 the value of (cpuid.4.eax[31:26] +1) 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

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Intel ARCHITECTURE IA-32 User Manual Page 307

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