RT-Thread的CPU使用率計算

CPU 的使用率一般是我們比較關心的問題，在這里我們就用空閑線程的鈎子函數去統計 CPU 的使用率，並通過串口打印出來。
首先我們在初始化線程中設置好鈎子函數，並在 LED 線程中給系統人為的加入很多“事情”，讓其占用率變高，方便統計，然后每個 1 秒中打印一次 CPU 使用率。其中 CPU 的使用率我們是根據 CPU 的空閑率反推出來的。

#include <rtthread.h>
#include <rthw.h>

#define CPU_USAGE_CALC_TICK    10
#define CPU_USAGE_LOOP        100

static rt_uint8_t  cpu_usage_major = 0, cpu_usage_minor= 0;
static rt_uint32_t total_count = 0;

static void cpu_usage_idle_hook(void)
{
    rt_tick_t tick;
    rt_uint32_t count;
    volatile rt_uint32_t loop;

    if (total_count == 0)
    {
        /* get total count */
        rt_enter_critical();
        tick = rt_tick_get();
        while(rt_tick_get() - tick < CPU_USAGE_CALC_TICK)
        {
            total_count ++;
            loop = 0;

            while (loop < CPU_USAGE_LOOP) loop ++;
        }
        rt_exit_critical();
    }

    count = 0;
    /* get CPU usage */
    tick = rt_tick_get();
    while (rt_tick_get() - tick < CPU_USAGE_CALC_TICK)
    {
        count ++;
        loop  = 0;
        while (loop < CPU_USAGE_LOOP) loop ++;
    }

    /* calculate major and minor */
    if (count < total_count)
    {
        count = total_count - count;
        cpu_usage_major = (count * 100) / total_count;
        cpu_usage_minor = ((count * 100) % total_count) * 100 / total_count;
    }
    else
    {
        total_count = count;

        /* no CPU usage */
        cpu_usage_major = 0;
        cpu_usage_minor = 0;
    }
}

void cpu_usage_get(rt_uint8_t *major, rt_uint8_t *minor)
{
    RT_ASSERT(major != RT_NULL);
    RT_ASSERT(minor != RT_NULL);

    *major = cpu_usage_major;
    *minor = cpu_usage_minor;
}

void cpu_usage_init(void)
{
    /* set idle thread hook */
    rt_thread_idle_sethook(cpu_usage_idle_hook);
}

前面說過，系統的心跳時鍾過快，會增加 cpu 的負擔，我們可以在這里來驗證，讀者可
以將系統滴答時間改為 1ms，然后你將會發現 cpu 的使用率從 24%升高到了 87%!!,如下圖：