pthread_cond_timedwait() : time internal resolution issue.

[Joel Sherrill]

You have to configure the clock tick length. By default it is 10
milliseconds if I remember correctly. All timeouts are done in the clock
tick.

By using main() as the entry point and not specifying any configuration
info you are getting the entire default settings.

On Aug 14, 2017 12:19 AM, "Thomas Kim" <thomas73.kim at gmail.com> wrote:

> Dear Sir,
>
> I am testing pthread_cond_timedwait() on realview-pbx-a9 using QEMU.
>
> My testing code is below;
>
> #include <pthread.h>
> #include <time.h>
> static void thread_sleep(struct timespec *ti)
> {
>     pthread_mutex_t mtx;
>     pthread_cond_t cnd;
>     pthread_mutex_init(&mtx, 0);
>     pthread_cond_init(&cnd, 0);
>     pthread_mutex_lock(&mtx);
>     pthread_cond_timedwait(&cnd, &mtx, ti);
>     pthread_mutex_unlock(&mtx);
>     pthread_cond_destroy(&cnd);
>     pthread_mutex_destroy(&mtx);
> }
> void own_msleep(unsigned long msecs)
> {
>     struct timeval tv;
>     gettimeofday(&tv, 0);
>     struct timespec ti;
>     ti.tv_nsec = (tv.tv_usec + (msecs % 1000) * 1000) * 1000;
>     ti.tv_sec = tv.tv_sec + (msecs / 1000) + (ti.tv_nsec / 1000000000);
>     ti.tv_nsec %= 1000000000;
>     thread_sleep(&ti);
> }
> #define TEST_1 0
> #define TEST_2 0
> #define TEST_3 0
> #define TEST_4 1
> int main(int argc, char *argv[])
> {
>  int count = 0;
>
>  while (1)
>  {
> #if TEST_1 // Normal operation. total time for count 100 = almost 1 second.
>   own_msleep(10);
>   count++;
>   if (count%100 == 0) printf("count=%d\n", count);
> #endif
> #if TEST_2 // Abnormal operation. total time for count 200 = about 2
> seconds.
>   own_msleep(5);
>   count++;
>   if (count%200 == 0) printf("count=%d\n", count);
> #endif
> #if TEST_3 // Abnormal operation. total time for count 500 = about 5
> seconds.
>   own_msleep(2);
>   count++;
>   if (count%500 == 0) printf("count=%d\n", count);
> #endif
> #if TEST_4 // Abnormal operation. total time for count 1000 = about 10
> seconds.
>   own_msleep(1);
>   count++;
>   if (count%1000 == 0) printf("count=%d\n", count);
> #endif
>  }
>  return 0;
> }
>
> As you see in my testing code, I called own_msleep() function using
> pthread mutex, condition variable API.
>
> As my result, when I use own_msleep(10), there is not any problem for this.
> But, when I decrease time internal from 10ms to (5 or 2 or 1)ms, msleep()
> have addtional delay.
>
> As I know from BSP code for realview-pbx-a9, OS timer interval is 1ms.
>
> Is it correct behaivor ?
> Is there any limitation for using short time interval ?
>
> Please advise me.
>
> Best Regards,
> Thomas Kim.
>
>
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