Created
June 13, 2014 15:01
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| // It's a CPU-bound program for testing | |
| #include <stdio.h> | |
| #include <pthread.h> | |
| #include <unistd.h> | |
| static size_t num_slices; | |
| static size_t num_cpus; | |
| static pthread_mutex_t pi_lock; | |
| static double pi; | |
| void* pi_calc(void* pid) { | |
| size_t rank = (size_t) pid; | |
| double precision = 1.0 / num_slices; | |
| double slice = 0; | |
| double sum = 0; | |
| for (size_t i = rank; i < num_slices; i += num_cpus) { | |
| slice = precision * (0.5 + i); | |
| sum += 4.0 / (1.0 + slice * slice); | |
| } | |
| pthread_mutex_lock(&pi_lock); | |
| pi += sum * precision; | |
| pthread_mutex_unlock(&pi_lock); | |
| return NULL; | |
| } | |
| int main () | |
| { | |
| num_slices = 1 << 16; | |
| num_cpus = sysconf(_SC_NPROCESSORS_CONF); | |
| pi = 0; | |
| pthread_mutex_init(&pi_lock, NULL); | |
| pthread_t threads[num_cpus]; | |
| for (size_t i = 0; i < num_cpus; i++) { | |
| cpu_set_t cpuset; | |
| CPU_ZERO(&cpuset); | |
| CPU_SET(i, &cpuset); | |
| pthread_attr_t attr; | |
| pthread_attr_init(&attr); | |
| // only availbale in Linux, to reduce the number of context switch across many cores | |
| pthread_attr_setaffinity_np(&attr, sizeof(cpu_set_t), &cpuset); | |
| // increase the time slice, to reduce the total number of context switch | |
| pthread_attr_setschedpolicy(&attr, SCHED_BATCH); | |
| pthread_create(&threads[i], &attr, pi_calc, (void *) i); | |
| pthread_attr_destroy(&attr); | |
| } | |
| for (size_t i = 0; i < num_cpus; i++) { | |
| pthread_join(threads[i], NULL); | |
| } | |
| printf("pi = %16.16lf\n", pi); | |
| return 0; | |
| } |
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