topic Newbie? Is there a way to deteremine HTT support and enabled/di in Intel® Moderncode for Parallel Architectures

Newbie? Is there a way to deteremine HTT support and enabled/disabled from a windows API?

Dave_Thompson — Wed, 21 Apr 2010 17:14:36 GMT

I know how to check CPUID Leaf 1 edx bit 28 for the presence of the HTT, but I want a way with out using the CPUID instruction.

That will give me HTT available.

The bios supplies the setting of HTT.

Is there a way of checking that setting usinga Windows API?

I am perfectly willing to accept registry queries.

Newbie? Is there a way to deteremine HTT support and enabled/di

Roman_D_Intel — Wed, 12 May 2010 15:04:09 GMT

Hi,

Windows XP SP3 and following versions support GetLogicalProcessorInformation API call. The example in http://msdn.microsoft.com/en-us/library/ms683194(VS.85).aspxcomputes logical and physical core counts using the GetLogicalProcessorInformation function. One way of determining if HT is onon current Intel CPUs is to comparethese two numbers(i.e.if "processorCoreCount
Best regards,
Roman

Newbie? Is there a way to deteremine HTT support and enabled/di

Dave_Thompson — Wed, 12 May 2010 15:26:41 GMT

Hi Roman,

Thanks for your reply. I have been working pretty hard at this and have discovered the answer, after a lot of digging. You are correct in your statements, but you have to take it one step further.

int chips = 0;

int cores = 0;

int buses = 0;

int threads = 0;

int total = 0;

int cache[4] = { 0 };

bool threading = false;

/* requires WinXp SP3 or Win2003 SP1 */

PSYSTEM_LOGICAL_PROCESSOR_INFORMATION pInfo = NULL;

int size = 0;

GetLogicalProcessorInformation( pInfo, &size );

pInfo = alloca( size ); /* on the stack */

if ( ! pInfo ) exit( 3 );

memset( pInfo, 0, size );

if ( ! GetLogicalProcessorInformation( pInfo, &size ) ) exit( 4 );

while ( size )

{

switch ( pInfo->Relationship )

{

case RelationNumaNode:

buses++;

break;

case RelationProcessorCore:

cores++;

threads = CountBits( (unsigned int)pInfo->ProcessorMask );

total += threads;

if ( pInfo->ProcessorCore.Flags == 1 )

threading = true;

break;

case RelationProcessorPackage:

chips++;

break;

case RelationCache:

cache[ pInfo->Cache.Level ] = pInfo->Cache.Size;

break;

default:

exit( 5 );

}

size -= sizeof *pInfo;

pInfo++;

}

It has to do with the ProcessorCore.Flags being set to one.
Unfortunately this is also true in the case of a VMware Guest which leads to a whole set of additional issues.

I have also indirectly seen this from a customer using this approach,
total = 2 chips = 1 cores = 1 threads = 2 threading = true
The chip was a "Intel Core2 CPU 6400 @ 2.13GHz".
I am at a complete loss at explaining this.This is the only instance that I have seen or heard of. I have asked the customer to check for a BIOS upgrade. The only other explanation I have, would be some sort of virtualization being present. I am 98% sure it's not VMware.

Newbie? Is there a way to deteremine HTT support and enabled/di

Roman_D_Intel — Fri, 14 May 2010 11:09:41 GMT

Dave, I should have stated that this method works on Windows Vista+ and not on Windows XP SP3+.The documentation ofSYSTEM_LOGICAL_PROCESSOR_INFORMATION data structrurementions this misbehaviour on Windows XP.

Windows Server 2003 and Windows XP Professional x64 Edition: [...] Therefore, to determine whether the processor supports multiple cores or hyperthreading on systems prior to Windows Vista, use the CPUID instruction.