How How can I change the MINIX Operating System to favor IO bound processes rather than CPU bound processes?

Question

The scheduler currently uses round robin to schedule. I have access to the user time and system time of each process.

USER TIME OF HEAD

rdy_head[USER_Q]->user_time

SYSTEM TIME OF HEAD

rdy_head[USER_Q]->user_time

I need to favor IO bound processes, but cpu bound processes cannot be completely starved.

Any ideas?

/*===========================================================================*
 *              sched                        * 
 *===========================================================================*/
PRIVATE void sched()
{
/* The current process has run too long.  If another low priority (user)
 * process is runnable, put the current process on the end of the user queue,
 * possibly promoting another user to head of the queue.
 */

  if (rdy_head[USER_Q] == NIL_PROC) return;

  /* One or more user processes queued. */
  rdy_tail[USER_Q]->p_nextready = rdy_head[USER_Q];
  rdy_tail[USER_Q] = rdy_head[USER_Q];
  rdy_head[USER_Q] = rdy_head[USER_Q]->p_nextready;
  rdy_tail[USER_Q]->p_nextready = NIL_PROC;

  pick_proc();

}