QNX/UNIX: Анатомия параллелизма

  pthread_create(&tids[i], NULL, threadfunc, NULL);

 for (int i = 0; i < numpar; i++)

  pthread_join(tids[i], NULL);

 t = ClockCycles - t;

 cout << "Threads scheduling time " << cycle2milisec(t)

  << " msec. [" << t << " cycles]" << endl;

 ClockPeriod(CLOCK_REALTIME, &clcold, NULL, 0);

 exit(EXIT_SUCCESS);

}

Наконец, для сравнительного анализа выполним тот же объем вычислительной работы в одиночном потоке, то есть в последовательной «классической» программе ( файл p4-3.cc):

i nt main(int argc, char *argv[]) {

 int numpar = 1;

 if (argc > 1 && atoi(argv[1]) > 0)

  numpar = atoi(argv[1]);

 _clockperiod clcold;

 ClockPeriod(CLOCK_REALTIME, NULL, &clcold, 0);

 if (argc > 2 && atoi(argv[2]) > 0) {

  _clockperiod clcnew = { atoi(argv[2]) * 1000, 0 };

  ClockPeriod(CLOCK_REALTIME, &clcnew, &clcold, 0);

 }

 timespec interval;

 sched_rr_get_interval(0, &interval);

 cout << "Rescheduling interval = "

  << (double)interval.tv_nsec / 1000000. << " msec." << endl;

 uint64_t t = ClockCycles;

 workproc(1000 * numpar);

 t = ClockCycles - t;

 cout << "Single scheduling time. " << cycle2milisec(t)

  << " msec. [" << t << " cycles]" << endl;

 ClockPeriod(CLOCK_REALTIME, &clcold, NULL, 0);

 exit(EXIT_SUCCESS);

}

Выполняем 3 полученных теста для различных значений периода системного тика (показано группами по 3 запуска) в таком порядке: одиночный процесс, параллельные потоки, параллельные процессы:

# nice -n-19 p4-3 10

Rescheduling interval = 3.99939 msec

Single scheduling time: 5928.8 msec [3169850746 cycles]

# nice -n-19 p4-2 10

Rescheduling interval = 3.99939 msec.

Threads scheduling time: 5919.82 msec. [3165049513 cycles]

# nice -n-19 p4-1 10

Rescheduling interval = 3.99939 msec.

Forks scheduling time: 5962.21 msec. [3187713371 cycles]

# nice -n-19 p4-3 10 50

Rescheduling interval = 0.197788 msec

Single scheduling time: 6427.33 msec. [3436394566 cycles]

# nice -n-19 p4-2 10 50

Rescheduling interval = 0.197788 msec.

Threads scheduling time: 6207.96 msec. [3319104030 cycles]

# nice -n-19 p4-1 10 50

Rescheduling interval = 0.197788 msec

Forks scheduling time 6029.23 msec. [3223548073 cycles]

# nice -n-19 p4-3 10 20

Rescheduling interval = 0.077104 msec.

Single scheduling time: 6745.37 msec. [3606433666 cycles]

# nice -n-19 p4-2 10 20

Rescheduling interval = 0.077104 msec

Threads scheduling time: 6762.69 msec [3615692975 cycles]

# nice -n-19 p4-1 10 20

Rescheduling interval = 0.077104 msec

Forks scheduling time: 6647.42 msec [3554062343 cycles]

# nice -n-19 p4-3 10 11

Rescheduling interval = 0.04358 msec

Single scheduling time. 7517.74 msec [4019381476 cycles]

# nice -n-19 p4-2 10 11

Rescheduling interval = 0.04358 msec

Threads scheduling time: 7638.89 msec. [4084155676 cycles]

# nice -n-19 p4-1 10 11

Rescheduling interval = 0.04358 msec.