计算 Linux CPU 利用率

在 Linux 系统中的 /proc/stat 文件中存储了CPU 活动的信息，该文件中的所有值都是从系统启动开始累计到当前时刻。不同内核版本中该文件的格式可能不大一致，以下通过实例来说明数据该文件中各字段的含义。

$ cat /proc/stat 
cpu  1594121 406 1239990 396233700 162305 0 3641 0 0 0
cpu0 761327 194 604191 198151599 83873 0 1789 0 0 0
cpu1 832793 211 635798 198082101 78432 0 1852 0 0 0
intr 985115307 38 10 0 0 58 0 3 0 0 0 0 36 15 0 0 0 0 0 0 0 0 0 0 0 0 2473171 42 0 862348 0 57 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
ctxt 1896726060
btime 1592793001
processes 63407
procs_running 1
procs_blocked 0
softirq 191297272 3 90057502 70 10686595 0 0 34 51485476 0 39067592

第一行的数值表示的是CPU总的使用情况，所以我们只要用第一行的数字计算就可以了。下表解析第一行各数值的含义：

注：jiffies是内核中的一个全局变量，用来记录自系统启动一来产生的节拍数，在 linux 中，一个节拍大致可理解为操作系统进程调度的最小时间片，不同 linux 内核可能值有不同，通常在 1ms 到 10ms 之间

totalCpuTime = user + nice + system + idle + iowait + irq + softirq + stealstolen + guest + guest_nice
cpu使用率计算：

1. 请在一段时间内（推荐：必须大于0s，小于等于1s），获取两次cpu时间分配信息。
2. 计算两次的cpu总时间：total_2 - total_1
3. 计算两次的cpu剩余时间：idle_2 - idle_1
4. 计算两次的cpu使用时间：used = (total_2 - total_1) - (idle_2 - idle_1)
5. cpu使用率 = 使用时间 / 总时间 100% = used / total 100%

us: User time       -> %us = (User + Nice) / totalCpuTime * 100%
sy: System time     -> %sy = (System + Hard Irq + SoftIRQ) / totalCpuTime
ni: Nick time       -> %ni = (Nice) / totalCpuTime * 100%
id: Idle time       -> %id = (Idle) / totalCpuTime * 100%
wa: Waiting time    -> %wa = (Waiting) / totalCputTime * 100%
hi: Hard Irq time   -> %hi = (Hard Irq) / totalCpuTime * 100%
si: SoftIrq time    -> %si = (SoftRQ) / totalCpuTime * 100%
st: Steal time      -> %st = (Steal) / totalCputTime * 100%

程序实现（C）

首先定义一个结构体存放获取到的信息：

struct CPU_INFO
{
    char name[10];
    unsigned int user;
    unsigned int nice;
    unsigned int system;
    unsigned int idle;
    unsigned int iowait;
    unsigned int irq;
    unsigned int softirq;
    unsigned int stealstolen;
    unsigned int guest;
    unsigned int guest_nice;
};

定义两个函数用于获取信息和计算：

void  get_occupy (Cpu_info *o)
{
    FILE *fd;
    char buff[MAXBUFSIZE];
    fd = fopen ("/proc/stat", "r"); //这里只读取stat文件的第一行及cpu总信息，如需获取每核cpu的使用情况，请分析stat文件的接下来几行。
    fgets (buff, sizeof(buff), fd);
    // printf("get thr cpu info: %s", buff);
    sscanf (buff, "%s  %u %u %u %u %u %u %u %u %u %u", o->name, &o->user, &o->nice, &o->system, &o->idle, &o->iowait, &o->irq, &o->softirq, &o->stealstolen, &o->guest, &o->guest_nice);
    // printf("name=%s, user=%d, nice=%d, system=%d, idle=%d, iowait=%d, irq=%d, softirq=%d, stralstolen=%d, guest=%d, guest_nice=%d\n", o->name, o->user, o->nice, o->system, o->idle, o->iowait, o->irq, o->softirq, o->stealstolen, o->guest, o->guest_nice);
    fclose(fd);
}

float  cal_occupy (Cpu_info *o, Cpu_info *n)
{
    int ototal, ntotal;
    int oused, nused;

    ototal = (o->user + o->nice + o->system + o->idle + o->iowait + o-> irq + o-> softirq + o->stealstolen + o->guest + o->guest_nice);
    ntotal = (n->user + n->nice + n->system + n->idle + n->iowait + n-> irq + n-> softirq + n->stealstolen + n->guest + n->guest_nice);

    oused = ototal - o->idle;
    nused = ntotal - n->idle;

    // printf("ototal time: %d\n", ototal);
    // printf("ntotal time: %d\n", ntotal);

    // printf("oused time: %d\n", oused);
    // printf("nused time: %d\n", nused);

    return (100.0 * (nused - oused) / (ntotal - ototal));
}

最后主程序调用即可：

Cpu_info ocpu,ncpu;
    printf("Start the new thread to monitor key system values.\n");
    while(1)
    {
        //获取cpu使用率
        get_occupy(&ocpu);
        sleep(1);
        get_occupy(&ncpu);
        printf("CPU Usage(%): %8.4f\n", cal_occupy(&ocpu, &ncpu));
    }