How do I count CPU cores?

khb

Hi together, I'd like to determine the number of cores a CPU has using a C++ program. I found a solution at http://www.intel.com on how to do it for Intel CPUs. But I didn't find out how to do it for AMD CPUs (i.e., Athlon X2). Moreover, the Intel solution states that it might give wrong results for CPUs with a certain stepping if it's not compiled on that CPU type :( Therefore I'd like to ask if anybody has a robust solution for counting the cores of Intel and AMD CPUs. Thank you for any ideas in advance! Regards, Marcus.

David Crow

Use the Win32_Processor class.

"Money talks. When my money starts to talk, I get a bill to shut it up." - Frank

"Judge not by the eye but by the heart." - Native American Proverb

khb

Hi David, thank you for the hint. I managed to access the Win32_Processor members. However, the members NumberOfCores and NumberOfLogicalProcessors are not valid. To get them MSDN suggests to use Win32_ComputerSystemProcessor. This class contains a reference to Win32_Processor which should contain the data I'm looking for. Now my question: How do I follow the reference from Win32_ComputerSystemProcessor to Win32_Processor in C++? In the first run I used ExecQuery() to select Win32_Processor and accessed its data using Next() and Get(). Now I guess I have to use ExecQuery() to select Win32_ComputerSystemProcessor, but how do I continue? Thank you for any help you can give! Regards, Marcus.

David Crow

khb wrote:

I managed to access the Win32_Processor members. However, the members NumberOfCores and NumberOfLogicalProcessors are not valid. To get them MSDN suggests to use Win32_ComputerSystemProcessor. This class contains a reference to Win32_Processor which should contain the data I'm looking for.

This makes no sense. If the members of Win32_Processor are not valid, why would you then state that they should contain the data you're looking for?

khb wrote:

However, the members NumberOfCores and NumberOfLogicalProcessors are not valid.

How are you verifying this?

"Money talks. When my money starts to talk, I get a bill to shut it up." - Frank

"Judge not by the eye but by the heart." - Native American Proverb

khb

DavidCrow wrote:

This makes no sense. If the members of Win32_Processor are not valid, why would you then state that they should contain the data you're looking for?

Maybe I understood wrong what MSDN says. I just read: "To determine the total number of processor instances associated with a computer system object, use the Win32_ComputerSystemProcessor association class."

DavidCrow wrote:

How are you verifying this?

Maybe I'm doing something wrong. I compiled the code with VC6 on my single core P4 with HT enabled (Win XP). I also run the program on a dual core Pentium D with HT enabled (also Win XP). In both cases NumberOfCores was not found and NumberOfLogicalProcessors was 0. I guess that the code works, as I can retrieve other members like, e.g., Name correctly. However, I can post the code if you like. Regards, Marcus.

David Crow

khb wrote:

In both cases NumberOfCores was not found and NumberOfLogicalProcessors was 0.

These were added for Vista. http://www.microsoft.com/technet/scriptcenter/topics/vista/wmi1.mspx[^] http://windowssdk.msdn.microsoft.com/en-us/library/ms738352.aspx[^]

"Money talks. When my money starts to talk, I get a bill to shut it up." - Frank

"Judge not by the eye but by the heart." - Native American Proverb

khb

DavidCrow wrote:

These were added for Vista.

Whoops, I somehow missed that :-O Well, this brings me right back to my initial question: Is there any chance to get the processor specs on non-Vista systems? Regards, Marcus.

David Crow

khb wrote:

Is there any chance to get the processor specs on non-Vista systems?

Yes, I've done it with both Win32_ComputerSystem and Win32_Processor.

"Money talks. When my money starts to talk, I get a bill to shut it up." - Frank

"Judge not by the eye but by the heart." - Native American Proverb

khb

Now I'm getting confused ;) I just tried Win32_ComputerSystem. For example, I can get NumberOfProcessors correctly. But I can't get NumberOfLogicalProcessors, it's not in the query result. But this is alright according to MSDN which says about NumberOfLogicalProcessors: Windows Server 2003, Windows XP, Windows 2000, Windows NT 4.0, and Windows Me/98/95: This property is not available. Then I tried Win32_Processor. For example, I can get Name correctly. But I get neither NumberOfLogicalProcessors nor NumberOfCores, they're both not in the query result. But again this is alright, because MSDN states for both properties what I already cited above. Or did I get something completely wrong? Thank you for your patience, David! Regards, Marcus.

Mike ONeill

::GetSystemInfo (which is available all the way back to Win95) will get you the number of processors. http://msdn.microsoft.com/library/en-us/sysinfo/base/getsysteminfo.asp[^] I don't know how it would interpret a hyper-threaded machine. For that you might try the cpuid instruction, which is available as a compiler intrinsic as __cpuid (see http://msdn2.microsoft.com/en-us/library/hskdteyh.aspx[^]) Mike

khb

Hi Mike, thanks for your answer. Currently I'm using the code from the article Counting Physical and Logical Processors here on CP. It makes also use of the functions you mentioned. I split up the code on did some tests on the following 2 PCs (I was wrong before: Pentium D has no HT):

Pentium 4, 3.06GHz, Single core, HT
Pentium D 950, 3.40GHz, Dual core, No HT

I'd like to calculate the following values:

CPUs: 1, #Cores: 1, #Log. CPUs per Core: 2
CPUs: 1, #Cores: 2, #Log. CPUs per Core: 1

Now the problem: The functions you mentioned return the following values for both(!) CPUs:

GetSystemInfo.dwNumberOfProcessors: 2
cpuid HTT bit: Set
cpuid # logical CPUs per physical CPU: 2

This shows that it's not possible to distinguish between HT and dual core :(( Regards, Marcus.

How do I count CPU cores?

CPUs: 1, #Cores: 1, #Log. CPUs per Core: 2

CPUs: 1, #Cores: 2, #Log. CPUs per Core: 1