进程调度API之wake_up_process

int wake_up_process(struct task_struct *p)这个函数用于唤醒一个task。其使用的例程如下：static void cmtp_reset_ctr(struct capi_ctr *ctrl){struct cmtp_session *session = ctrl->driverdata;BT_DBG("ctrl %p", ctrl);capi_ctr_down(ctrl);atomic_inc(&session->terminate);wake_up_process(session->task);}例如这个例子中就通过wake_up_process 来唤醒session->task其源码分析如下：int wake_up_process(struct task_struct *p){return try_to_wake_up(p, TASK_NORMAL, 0);}唤醒p到TASK_NORMAL 状态static inttry_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags){unsigned long flags;int cpu, success = 0;/* * If we are going to wake up a thread waiting for CONDITION we * need to ensure that CONDITION=1 done by the caller can not be * reordered with p->state check below. This pairs with mb() in * set_current_state() the waiting thread does. */smp_mb__before_spinlock();raw_spin_lock_irqsave(&p->pi_lock, flags);#如果task的状态已经等于要设的状态了，就退出吧，从这里知道，调用wake_up_process 不一定非得是sleep的task.正常task#也是可以的，只是不起作用而已，在这里就退出了.if (!(p->state & state))goto out;trace_sched_waking(p);/* We're going to change ->state: */success = 1;#获得要wakeup 的task 原本是运行到哪个cpu上的cpu = task_cpu(p);/* * Ensure we load p->on_rq _after_ p->state, otherwise it would * be possible to, falsely, observe p->on_rq == 0 and get stuck * in smp_cond_load_acquire() below. * * sched_ttwu_pending()                 try_to_wake_up() *   [S] p->on_rq = 1;                  [L] P->state *       UNLOCK rq->lock  -----. *                              \ * +---   RMB * schedule()                   / *       LOCK rq->lock    -----' *       UNLOCK rq->lock * * [task p] *   [S] p->state = UNINTERRUPTIBLE     [L] p->on_rq * * Pairs with the UNLOCK+LOCK on rq->lock from the * last wakeup of our task and the schedule that got our task * current. */smp_rmb();#要唤醒的task 不在自己的rq上，也就是要唤醒其他rq上的task，所以这里会做remote wake up.if (p->on_rq && ttwu_remote(p, wake_flags))goto stat;#ifdef CONFIG_SMP/* * Ensure we load p->on_cpu _after_ p->on_rq, otherwise it would be * possible to, falsely, observe p->on_cpu == 0. * * One must be running (->on_cpu == 1) in order to remove oneself * from the runqueue. * *  [S] ->on_cpu = 1;[L] ->on_rq *      UNLOCK rq->lock *RMB *      LOCK   rq->lock *  [S] ->on_rq = 0;    [L] ->on_cpu * * Pairs with the full barrier implied in the UNLOCK+LOCK on rq->lock * from the consecutive calls to schedule(); the first switching to our * task, the second putting it to sleep. */smp_rmb();/* * If the owning (remote) CPU is still in the middle of schedule() with * this task as prev, wait until its done referencing the task. * * Pairs with the smp_store_release() in finish_lock_switch(). * * This ensures that tasks getting woken will be fully ordered against * their previous state and preserve Program Order. */smp_cond_load_acquire(&p->on_cpu, !VAL);p->sched_contributes_to_load = !!task_contributes_to_load(p);#先将task的状态设置为TASK_WAKINGp->state = TASK_WAKING;#task 如果是在等待io的时候sleep。则先结束这次io 操作？if (p->in_iowait) {delayacct_blkio_end();atomic_dec(&task_rq(p)->nr_iowait);}#根据wakup cpu选择要rq要运行到哪个cpu上cpu = select_task_rq(p, p->wake_cpu, SD_BALANCE_WAKE, wake_flags);#如果wakeup后的cpu 和之前task 运行的cpu 不相等，则设置需要迁移的flag，方便以后进行迁移工作。并通过set_task_cpu将task #wakeup 后的cpu保存在task中if (task_cpu(p) != cpu) {wake_flags |= WF_MIGRATED;set_task_cpu(p, cpu);}#else /* CONFIG_SMP */if (p->in_iowait) {delayacct_blkio_end();atomic_dec(&task_rq(p)->nr_iowait);}#endif /* CONFIG_SMP */#执行wakeup task 的操作ttwu_queue(p, cpu, wake_flags);stat:#更新rq中相关统计数据ttwu_stat(p, cpu, wake_flags);out:raw_spin_unlock_irqrestore(&p->pi_lock, flags);return success;}