clock_gettime 不能立即更新 [英] clock_gettime can not update instantly

问题描述

更新

检查时间分辨率后，我们尝试在内核空间调试问题.

After checking the time resolution, we tried to debug the problem in kernel space.

unsigned long long task_sched_runtime(struct task_struct *p)
{
    unsigned long flags;
    struct rq *rq;
    u64 ns = 0;

    rq = task_rq_lock(p, &flags);
    ns = p->se.sum_exec_runtime + do_task_delta_exec(p, rq);
    task_rq_unlock(rq, &flags);

    //printk("task_sched runtime\n");
    return ns; 
}

我们的新实验表明时间 p->se.sum_exec_runtime 不会立即更新.但是如果我们在函数内部添加 printk() .时间会即时更新.

Our new experiment shows that the time p->se.sum_exec_runtime is not updated instantly. But if we add printk() inside the function. the time will be updated instantly.

旧

我们正在开发一个 Android 程序.但是，函数 threadCpuTimenanos() 测量的时间在我们的平台上并不总是正确的.

We are developing an Android program. However, the time measured by the function threadCpuTimenanos() is not always correct on our platform.

经过实验，我们发现clock_gettime返回的时间不是即时更新的.即使经过几次 while 循环迭代，我们得到的时间仍然没有改变.

After experimenting, we found that the time returned from clock_gettime is not updated instantly. Even after several while loop iterations, the time we get still doesn't change.

这是我们的示例代码:

while(1)
{
    test = 1;
    test = clock_gettime(CLOCK_THREAD_CPUTIME_ID, &now);

    printf(" clock gettime test 1 %lx, %lx , ret = %d\n",now.tv_sec , now.tv_nsec,test );

    pre = now.tv_nsec;
    sleep(1);
}

此代码在 x86 PC 上运行正常.但是它不能在我们的内核为 2.6.35.13 的嵌入式平台 ARM Cortex-A9 中正确运行.

This code runs okay on an x86 PC. But it does not run correctly in our embedded platform ARM Cortex-A9 with kernel 2.6.35.13.

有什么想法吗?

推荐答案

我更改了 clock_gettime 以使用 CLOCK_MONOTONIC_RAW ，将线程分配给一个 CPU，但我得到了不同的值.我也在用双皮质-A9

I changed the clock_gettime to use the CLOCK_MONOTONIC_RAW , assigned the thread to one CPU and I get different values. I am also working with a dual cortex-A9

while(1)
{
    test = 1;
    test = clock_gettime(CLOCK_MONOTONIC_RAW, &now);

    printf(" clock gettime test 1 %lx, %lx , ret = %d\n",now.tv_sec , now.tv_nsec, test );

    pre = now.tv_nsec;
    sleep(1);
}

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