clock_gettime不能即时更新 [英] clock_gettime can not update instantly

问题描述

更新

检查时间分辨率后，我们试图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; 
}

我们的新的实验表明，该时间 P-GT＆; se.sum_exec_runtime 不更新即时。但是，如果我们添加的printk（）在函数内部。时间将即时更新。

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。
然而，时间的函数来测量 threadCpuTimenanos（）是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.

试验后，我们发现，从时间 clock_gettime 不更新立即返回。
即使经过多次而循环迭代，我们得到的还是时间不会改变。

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.

下面是我们的示例code：

Here's our sample code:

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);
}

这code运行在x86 PC上还好。不过，这并不正确地在我们的嵌入式平台的ARM Cortex-A9内核2.6.35.13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.

任何想法？

推荐答案

我改为使用CLOCK_MONOTONIC_RAW的clock_gettime，分配线程一个CPU，我得到不同的值。
我也有一个双核Cortex-A9工作

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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