工作中我们经常会遇到这样的问题，需要模拟cpu的负载程序，例如模拟cpu占有率抬升10%、20%、50%、70%等，那这样的程序应该如何实现呢？它的原理是什么样的呢？

思想

创建一个应用程序，该应用程序的作用可以根据用户的设置占用指定的cpu占有率。例如用户指定占用10%，则该应用程序占用cpu占有率为10%；若设置cpu占有率为50%，则应用程序程序的cpu占有率为50%。

占用固定cpu占有率的程序

#include <iostream>
#include <pthread.h>
#include <time.h>
#include <math.h>
#include <unistd.h>

using namespace std;

typedef long long int int64;
const int NUM_THREADS = 8; //CPU core nums
int INTERVAL = 100;
int cpuinfo = 70; //CPU utilization rate

// time unit is "ms"
int64 GetTickCount()
{
    timespec now;
    int64 sec, nsec;

    clock_gettime(CLOCK_MONOTONIC, &now);
    sec = now.tv_sec;
    nsec = now.tv_nsec;

    return sec * 1000 + nsec / 1000000;
}

void* CPUCost(void *args)
{
    int busyTime = INTERVAL * cpuinfo / 100;
    int idleTime = INTERVAL - busyTime;
    int64 startTime = 0;

    std::cout << "XXXX CPUCost" << std::endl;
    std::cout << "XXXX cpuinfo = " << cpuinfo << std::endl;

    /*
     * within INTERVAL ms, INTERVAL = busyTime + idleTime,
     * spend busyTime ms to let cpu busy,
     * spend idleTime ms top let cpu idle
     */
    while (true) {
        startTime = GetTickCount();
        while((GetTickCount() - startTime) <= busyTime);
        usleep(idleTime * 1000);
    }
}

int main(int argc, char **argv)
{
    pthread_t t[NUM_THREADS];
    int ret;

    std::cout << "please input cpu utilization rate" << std::endl;
    std::cin >> cpuinfo;
    for(int i = 0; i < NUM_THREADS; i++) {
        ret = pthread_create(&t[i], NULL, CPUCost, NULL);
        if(ret)
            std::cout << "XXXX create err" << std::endl;
        std::cout<<"pthread_create i= "<<i<<std::endl;
    }

    pthread_exit(NULL);
    return 0;
}

上文代码中NUM_THREADS变量的含义是cpu有几个核，该变量修改为cpu的核数；INTERVAL值默认为100，无需修改；cpuinfo，全局变量，用于保存应用程序占用的cpu占有率；GetTickCount函数的作用是获取毫秒时间；CPUCost函数是线程函数，核心逻辑：

    /*
     * within INTERVAL ms, INTERVAL = busyTime + idleTime,
     * spend busyTime ms to let cpu busy,
     * spend idleTime ms top let cpu idle
     */
    while (true) 
    {
        startTime = GetTickCount();  //获取一个开始时间，单位为ms
        //busyTime和idleTime的总和为100ms，即在100ms的时间间隔内，程序运行时间为//busyTime，程序空闲时间为idleTime，通过这样的方式来控制cpu占用率，如下的是循环是控制程序运行busyTime时间
        while((GetTickCount() - startTime) <= busyTime);
//usleep控制程序睡眠idleTime时间，让出cpu
        usleep(idleTime * 1000);
    }

注意事项：

由于我的环境cpu有8个核，若指定cpu占有率的为70%，则每个核的cpu占有率为70%，总的cpu占有率为70%，所有的cpu核占有率综合为560%左右（70%*8）。

运行结果如下所示：

可以看到cpu各个核的cpu占有率均在70%以上，综合的cpu占有率也是79%，各个核的cpu占有率总计为520.9基本与预期相符，达到预期目的。

cpu占有率动态变化程序（按照正弦函数规律控制cpu占有率）

代码如下所示：

#include <iostream>
#include <pthread.h>
#include <time.h>
#include <math.h>
#include <unistd.h>
#include <math.h>

using namespace std;

#define PI acos(-1)
#define DISCRETEVALUE 100
typedef long long int int64;
const int NUM_THREADS = 8; //CPU core nums
int INTERVAL = 100;
int cpuinfo = 70; //CPU utilization rate

// time unit is "ms"
int64 GetTickCount()
{
    timespec now;
    int64 sec, nsec;

    clock_gettime(CLOCK_MONOTONIC, &now);
    sec = now.tv_sec;
    nsec = now.tv_nsec;

    return sec * 1000 + nsec / 1000000;
}

void* CPUCost(void *args)
{
//    int busyTime = INTERVAL * cpuinfo / 100;
//    int idleTime = INTERVAL - busyTime;
//    int64 startTime = 0;
    int busyTime = 50;
    int idleTime = 50;
    int64 startTime = 0;
    //每次递增间隔
    float value = 2*PI/DISCRETEVALUE;
    int index = 0;

    cout<<"value = "<<value <<" PI = "<<sin(PI)<<endl;
    std::cout << "XXXX CPUCost" << std::endl;
    std::cout << "XXXX cpuinfo = " << cpuinfo << std::endl;

    /*
     * within INTERVAL ms, INTERVAL = busyTime + idleTime,
     * spend busyTime ms to let cpu busy,
     * spend idleTime ms top let cpu idle
     */
    while (true) {
        startTime = GetTickCount();
        while((GetTickCount() - startTime) <= busyTime);
        usleep(idleTime * 1000);
        //添加正弦曲线，
        if(index > DISCRETEVALUE)
            index = 0;
        busyTime = 50 + sin(index*value)*50;
        idleTime = 100 - busyTime;
        cout<<"busyTime = "<<busyTime<<"  idleTime = "<<idleTime << "index*value = "<< index*value<<"  sin(index*value)*50 = "<<sin(index*value)*50<<endl;
        index++;
    }
}

int main(int argc, char **argv)
{
    pthread_t t[NUM_THREADS];
    int ret;

    std::cout << "please input cpu utilization rate" << std::endl;
    std::cin >> cpuinfo;

    for(int i = 0; i < NUM_THREADS; i++) {
        ret = pthread_create(&t[i], NULL, CPUCost, NULL);
        if(ret)
            std::cout << "XXXX create err" << std::endl;
        std::cout<<"pthread_create i= "<<i<<std::endl;
    }

    pthread_exit(NULL);
    return 0;
}

结果显示

 完美实现cpu占有率动态控制。

总结

核心思想是在100ms内动态的分配应用程序运行时间和空闲时间的比例，从而实现达到控制cpu占有率的目的。