Lock performance

#include <tchar.h>
#include <iostream>

#include <Windows.h>

#include <boost/thread.hpp>

class CTimer
{
    static double TicksPerSecond()
    {
        LARGE_INTEGER nFreq;

        ::QueryPerformanceFrequency( &nFreq );

        return nFreq.QuadPart / 1000000.0;
    }

public:

    CTimer()
    {
        reset();
    }

    //! Returns current (system) time in microseconds.
    double tick() const
    {
        LARGE_INTEGER nCounter;

        ::QueryPerformanceCounter( &nCounter );

        return nCounter.QuadPart / m_sdTicksPerSecond;
    }

    //! Resets timer and returns current (system) time in microseconds.
    double reset()
    {
        m_dLast = tick();
        return m_dLast;
    }

    //! Returns elapsed time in microseconds since last reset(), then resets timer.
    double lap()
    {
        double t = m_dLast;
        m_dLast  = tick();
        return m_dLast - t;
    }

private:

    double        m_dLast;
    static double m_sdTicksPerSecond;
};

double CTimer::m_sdTicksPerSecond = CTimer::TicksPerSecond();

#define N 100000000
#define K 10

volatile long n = 0;

void TP_NL()
{
    __asm mov eax, 1;
    for( size_t i = 0; i < N; ++i )
    {
        __asm xadd dword ptr[n], eax;
    }
}

void TP_L()
{
    __asm mov eax, 1;
    for( size_t i = 0; i < N; ++i )
    {
        __asm lock xadd dword ptr[n], eax;
    }
}

int _tmain( int argc, _TCHAR* argv[] )
{
    //SetProcessAffinityMask( GetCurrentProcess(), 1 );
    SetThreadAffinityMask( GetCurrentThread(), 1 );

    auto DoTest =
        []( void (*pFunc)() )
        {
            std::vector< boost::thread > oVec;
            oVec.reserve( K );

            CTimer oTimer;

            for( size_t i = 0; i < K; ++i )
            {
                oVec.push_back( boost::thread( pFunc ) );
            }

            for( size_t i = 0; i < K; ++i )
            {
                oVec[i].join();
            }

            double d = oTimer.lap() * 1e3 / double( N ) / double( K );

            std::cout << "const of one operation: " << d << " ns." << std::endl;
        };

    DoTest( &TP_NL );
    DoTest( &TP_L );

    return 0;
}