论新进程的加入 --- Linux kernel

/*
 *    1 . 我们添加一个 tracepoint 来看下该函数的执行通路
 *    2 . 该函数在设计的时候做了怎么样的考虑
 *    3 . 该函数可以优化的地方
 *    4 . 实验验证.
 */
 /*
  *    该函数的唯一调用者是 copy_process(). 我们先来看下它的参数，然后再看它的执行通路.
  *    @p 
  * 	 copy_process() {
  * 	 	dup_task_struct() {
  * 			alloc_task_struct_node()
  * 			.....
  * 		}
  *      }
  *    @clone_flags
  *    vfork 暂且不考虑.
  *    SYSCALL_DEFINE0(fork)
       {
	      struct kernel_clone_args args = {
		     .exit_signal = SIGCHLD,
	      };
	      return kernel_clone(&args);
       }
  */
int sched_fork(unsigned long clone_flags, struct task_struct *p)
{
	__sched_fork(clone_flags, p);
	...
	...
	if (dl_prio(p->prio))
		return -EAGAIN;
	else if (rt_prio(p->prio))
		p->sched_class = &rt_sched_class;
	else
		p->sched_class = &fair_sched_class;
}
static void __sched_fork(unsigned long clone_flags, struct task_struct *p)
{
	p->on_rq			= 0;

	p->se.on_rq			= 0;
	p->se.exec_start		= 0;
	p->se.sum_exec_runtime		= 0;
	p->se.prev_sum_exec_runtime	= 0;
	p->se.nr_migrations		= 0;
	p->se.vruntime			= 0;
	INIT_LIST_HEAD(&p->se.group_node);

#ifdef CONFIG_FAIR_GROUP_SCHED
	p->se.cfs_rq			= NULL;
#endif

#ifdef CONFIG_SCHEDSTATS
	/* Even if schedstat is disabled, there should not be garbage */
	memset(&p->se.statistics, 0, sizeof(p->se.statistics));
#endif

	RB_CLEAR_NODE(&p->dl.rb_node);
	init_dl_task_timer(&p->dl);
	init_dl_inactive_task_timer(&p->dl);
	__dl_clear_params(p);

	INIT_LIST_HEAD(&p->rt.run_list);
	p->rt.timeout		= 0;
	p->rt.time_slice	= sched_rr_timeslice;
	p->rt.on_rq		= 0;
	p->rt.on_list		= 0;

#ifdef CONFIG_PREEMPT_NOTIFIERS
	INIT_HLIST_HEAD(&p->preempt_notifiers);
#endif

#ifdef CONFIG_COMPACTION
	p->capture_control = NULL;
#endif
	init_numa_balancing(clone_flags, p);
#ifdef CONFIG_SMP
	p->wake_entry.u_flags = CSD_TYPE_TTWU;
#endif
}