Counting Physical and Logical Processors

• Download demo project - 15.4 Kb

Introduction

Contemporary Intel Pentium IV processors support the so called Hyper-Threading mode. With Hyper-Threading, a real physical processor presents itself to the operating system as two independent logical processors. Hyper-Threading technology lessens process switching overhead, increasing overall system throughput. But in some calculation intensive applications, this delusion of two logical processors may lead to the loss of effectiveness if the program will start two parallel threads, which will compete for one physical processor. Thus we have to determine how many physical processors we have in our computer to adjust the number of parallel threads to the number of physical processors. The latter utility shows how we can do it from a C# program.

Background

The CPU Counting utility is based on the following Intel documents and code samples:

• How to Determine Whether a Processor Supports Hyper-Threading Technology
• How to Associate Logical Processors to Physical Processors
• I have also used C++ code sample from Khang Nguyen's article.

Using the code

The CPU Counting utility consists of two parts - the client part and the server part. The client part written in C# calls the server function and displays its results. The server part actually determines the number of processors. It uses ASM commands extensively and therefore is written in managed C++.

The key part of the client is the call to the server function GetCPUCount.

int LogicalNum   = 0;  // Number of logical CPU per ONE PHYSICAL CPU
int PhysicalNum  = 0;  // Total number of physical processor
CPUCountStatus HTStatusFlag = 0;

HTStatusFlag = CPUCount.GetCPUCount(ref LogicalNum, ref PhysicalNum);

Don't forget to add namespace usage statement.

using CPUCounter;

Server part is implemented as a separate DLL, containing static function GetCPUCount of the class CPUCount.

// CPUCount.h

#pragma once

#using   <mscorlib.dll>
using namespace System;

namespace CPUCounter
{
    public __value enum CPUCountStatus
    {
        HT_NOT_CAPABLE,
        HT_ENABLED,
        HT_DISABLED,
        HT_SUPPORTED_NOT_ENABLED,
        HT_CANNOT_DETECT
    };

    public __value class CPUCount
    {
        public:
            static CPUCountStatus GetCPUCount(int __gc* LogicalNum, 
                                              int __gc* PhysicalNum);
    };

    unsigned int  HTSupported();
    unsigned int LogicalProcPerPhysicalProc();
    unsigned int GetAPIC_ID();
    CPUCountStatus DefineCPUCount(int __gc* LogicalNum, 
                                  int __gc* PhysicalNum);

}

Function GetCPUCount returns value of CPUCountStatus enum type. Meaning of CPUCountStatus values are:

To determine hyper-threading possibilities and the number of physical and logical processors in your computer, just copy the files CPUCounterClient.exe and CPUCounter.dll to some directory and run CPUCounterClient.exe.

History

This is the first version of the CPU counting utility.

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