linux kernel - Why is clock_nanosleep sleeping for 20 ms when it is configured to sleep for 10 ms? -

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i trying run task periodically every 10 ms. before executing task, want check consistency of clock_nanosleep. took 10 values check time clock_nanosleep sleeping, varying in between 19-22 ms, should 10 ms.

i running thread sched_fifo, pri-98, hrtimers enabled in linux. currently, using 3.14.29 linux kernel rt patch. clock_nanosleep require configuration in linux apart hrtimers?

below code snippet running:

struct timespec arr[20]; while(1) {     clock_gettime(clock_monotonic,&check1);     if(i<20) {         arr[i].tv_sec = check1.tv_sec;         arr[i].tv_nsec = check1.tv_nsec;         ++i;     }     check1.tv_nsec += p_ct->period;      clock_nanosleep(clock_monotonic, timer_abstime, &check1, null);      clock_gettime(clock_monotonic,&check);     if(i<20) {         arr[i].tv_sec = check.tv_sec;         arr[i].tv_nsec = check.tv_nsec;         ++i;     } }

  • check return values of clock_gettime , clock_nanosleep. maybe there interruption signal
  • run 2 sequenced clock_gettime , calculate average execution time of clock_gettime. don't think around 9-12ms, let's check

code:

int r1 = clock_gettime(clock_monotonic,&check1); int r2 = clock_gettime(clock_monotonic,&check);   if(i<20) {       arr[i].tv_sec = check1.tv_sec;       arr[i].tv_nsec = check1.tv_nsec;       ++i;   }   if(i<20) {       arr[i].tv_sec = check.tv_sec;       arr[i].tv_nsec = check.tv_nsec;       ++i;   }   printf("%d %d\n", r1, r2);

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