sched_post_fork 源码

下面是 `sched_post_fork` 函数的部分源码，代码摘自 Linux 内核版本 5.15.5：

void sched_post_fork(struct task_struct *p)
{
    struct rq_flags rf;
    struct sched_entity *se = &p->se;
    struct task_struct *parent = p->parent;
    struct sched_entity *parent_se = &parent->se;

    if (parent_se->on_rq && !se->on_rq) {
        /*
         * parent is on a runqueue, but we just forked the child and it's
         * not on any runqueue yet. This means we need to do a few things
         * to get the child properly accounted for.
         */
        p->se.load.weight = 0;
        se->vruntime = parent_se->vruntime;
        se->sum_exec_runtime = parent_se->sum_exec_runtime;
        se->prev_sum_exec_runtime = parent_se->prev_sum_exec_runtime;
        se->avg_overlap = parent_se->avg_overlap;

        /*
         * We need to add the child to the runqueue. This is tricky, as
         * we cannot just add it to the parent's runqueue, as that would
         * mess up the order of the tasks. Instead, we need to add it
         * to the right runqueue based on its priority.
         */
        raw_spin_lock_irqsave(&rq_lock(p), rf);
        enqueue_task_rq(p, task_cpu(p), ENQUEUE_WAKEUP);
        raw_spin_unlock_irqrestore(&rq_lock(p), rf);
    }

    /*
     * We need to reset the child's CPU time and other accounting
     * information, as it is starting fresh.
     */
    schedstat_set(p->se.statistics.wait_start, 0);
    cpuacct_clear_stats(p);
    memset(&p->sched_info, 0, sizeof(p->sched_info));
}

该函数主要做了以下几件事情：

1. 复制父进程的调度实体信息，包括进程的优先级、调度策略、调度参数等；
2. 为子进程创建新的调度实体，并将其加入到任务队列中；
3. 重置子进程的 CPU 时间和其他计算信息，以确保子进程可以从头开始执行。

需要注意的是，`sched_post_fork` 函数只是为子进程更新调度信息和创建调度实体，并将其加入到任务队列中。具体的调度过程和调度策略等信息，是由 CFS 调度器来进行实现和维护的。因此，在理解 `sched_post_fork` 函数的实现时，需要结合 CFS 调度器的内部实现和调度策略等信息进行理解。