/*
 * This is a test program to reproduce a scheduling oddity I have found.
 *
 * (c) Balazs Scheidler
 *
 * Pass any argument to the program to set the CPU affinity.
 */
#define _GNU_SOURCE

#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <sys/time.h>
#include <time.h>
#include <sched.h>
              
/* diff in millisecs */
long
tv_diff(struct timeval *t1, struct timeval *t2)
{
  long long diff = (t2->tv_sec - t1->tv_sec) * 1e9 + (t2->tv_usec - t1->tv_usec);
  
  return diff /  1e6;
}

int 
reader(int fd)
{
  char buf[4096];
  int i;
  
  while (read(fd, buf, sizeof(buf)) > 0)
    {
      for (i = 0; i < 20000; i++)
        memset(buf, 'A'+i, sizeof(buf));
    }
  return 0;
}

int 
writer(int fd)
{
  char buf[4096];
  int i;
  int counter, prev_counter;
  struct timeval start, end, prev, now;
  long diff;
  
  memset(buf, 'A', sizeof(buf));
  
  counter = 0;
  prev_counter = 0;
  gettimeofday(&start, NULL);
  
  /* feed the other process with data while doing something that spins the CPU */
  while (write(fd, buf, sizeof(buf)) > 0)
    {
      for (i = 0; i < 100000; i++)
        memset(buf, 'A'+i, sizeof(buf));
        
      /* the rest of the loop is only to measure performance */
      counter++;
      gettimeofday(&now, NULL);
      if (now.tv_sec != prev.tv_sec)
        {
          diff = tv_diff(&prev, &now);
          printf("Check: %ld loops/sec, sum: %d \n", ((counter - prev_counter) * 1000) / diff, counter);
          prev_counter = counter;
        }
      if (now.tv_sec - start.tv_sec > 20)
        break;
      prev = now;
    }
  gettimeofday(&end, NULL);
  diff = tv_diff(&start, &end);
  printf("Final: %ld loops/sec, sum: %d\n", (counter*1000) / diff, counter);
  return 0;
}

int 
main(int argc, char *argv)
{
  int fds[2];
  cpu_set_t s;
  int set_affinity = 0;

  CPU_ZERO(&s);
  
  if (argc > 1)
    set_affinity = 1;
  
  pipe(fds);
  
  if (fork() == 0)
    {
      if (set_affinity)
        {
          CPU_SET(0, &s);
          sched_setaffinity(getpid(), sizeof(s), &s);
        }
      close(fds[1]);
      reader(fds[0]);
      return 0;
    }
  if (set_affinity)
    {
      CPU_SET(1, &s);
      sched_setaffinity(getpid(), sizeof(s), &s);
    }
  close(fds[0]);
  writer(fds[1]);
}