topology.c

# define _GNU_SOURCE
# include <stdio.h>
# include <stdlib.h>
# include <string.h>
# include <unistd.h>
# include <sched.h>

# define SYS_IND_CPU_PATH "/sys/devices/system/cpu/cpu"
# define KERNEL_MAX_CPU_PATH "/sys/devices/system/cpu/kernel_max"

int get_num_digits(int num) {
  int dig = 0;
  while(num > 0) {
    dig++;
    num = num / 10;
  }

  return dig;
}

int main(int argc, char **argv){

  cpu_set_t *thread_siblings, *core_siblings, *book_siblings, *set;
  int nbooks, nsockets, ncores, nthreads;
  FILE *fp;
  int maxcpus, ncpus=0, loopvar;
  char *cpu_string;

  /* Find the maximum number of CPUs allowed by the kernel*/
  fp = fopen(KERNEL_MAX_CPU_PATH, "r");
  fscanf(fp, "%d", &maxcpus);
  printf("Max number of CPUs allowed by Kernel %d\n", maxcpus);
  fclose(fp);

  /* Find the number of online CPUs*/
  for(loopvar = 0; loopvar < maxcpus; loopvar++)
    {
      cpu_string = malloc(strlen(SYS_IND_CPU_PATH) + get_num_digits(loopvar));
      sprintf(cpu_string, "%s%d", SYS_IND_CPU_PATH, loopvar);
      if (!access(cpu_string, R_OK)) {
        ncpus++;
        free(cpu_string);
      }
      else
        {
          free(cpu_string);
          break;
        }
    }
  printf("Online CPUs %d\n", ncpus);
  size_t setsize = CPU_ALLOC_SIZE(maxcpus);
  /* threads within one core */
  nthreads = CPU_COUNT_S(setsize, thread_siblings);
  /* cores within one socket */
  ncores = CPU_COUNT_S(setsize, core_siblings) / nthreads;
  /* number of sockets within one book */
  nsockets = ncpus / nthreads / ncores;
  /* number of books */
  nbooks = ncpus / nthreads / ncores / nsockets;

  return 0;
}