CPU speed, requires c++11 or c++0x

cpuTimer.cpp

#include <chrono>
#include <iostream>

#include <unistd.h>

class Timer {
private:
    static inline unsigned long long CPUCycleCounter(void) {
        unsigned long long int x;
        __asm__ volatile (".byte 0x0F, 0x31" : "=A" (x));
        return x;
    }
    unsigned long long _start;
    double _tdiv, _res;
    std::chrono::duration<long long int, std::ratio<1ll, 1000000ll> > _period;
    std::chrono::time_point<std::chrono::system_clock, std::chrono::duration<long long int, std::ratio<1ll, 1000000ll> > > _begin, _end;
    std::string _unit;
public:
    Timer() {
        clear();
        _tdiv = 1;
    }
    Timer(double t, std::string u) {
        clear();
        _tdiv = t;
        _unit = u;
    }
    void start() {
        clear();
        _begin = std::chrono::high_resolution_clock::now() ;
        _start = CPUCycleCounter();
    }
    void stop() {
        _res = ( CPUCycleCounter() - _start ) / _tdiv;
        _end = std::chrono::high_resolution_clock::now() ;
        _period = std::chrono::duration_cast<std::chrono::microseconds>(_end-_begin); 
    }
    void clear() {
        _start = _res = 0;        
    }
    std::string getRes() {
        return "Timer: " + std::to_string(_res) + _unit;
    }
    void test() {
        std::cout << "CPU appears to be " << (_res/_period.count())*1000000.0f << _unit<<"/s" << std::endl;
    }
};

class TimerGHz : public Timer {
public:
    TimerGHz() : Timer(1000000000.0f, "Ghz") {}
};

class TimerMHz : public Timer {
public:
    TimerMHz() : Timer(1000000.0f, "Mhz") {}
};


int main ()
{
    std::cout << "Calculating...\n" ;

    TimerGHz timer;

    timer.start();

    usleep(200);

    timer.stop();

    timer.test();
}