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文章系列

1.linux工作队列 - workqueue总览
2.linux工作队列 - workqueue_struct创建
3.linux工作队列 - 把work_struct加入工作队列
4.linux工作队列 - work_struct被调用过程

把work_struct加入工作队列

把work_struct加入到工作队列workqueue的API在系列文章1有介绍，这些API虽然用法不一，但是最终都会调用__queue_work（）函数来进行实际加入操作，比如API：queue_work_on：

bool queue_work_on(int cpu, struct workqueue_struct *wq,struct work_struct *work)
{bool ret = false;unsigned long flags;local_irq_save(flags);if (!test_and_set_bit(WORK_STRUCT_PENDING_BIT, work_data_bits(work))) {__queue_work(cpu, wq, work);------调用到__queue_workret = true;}local_irq_restore(flags);return ret;
}

下面分析__queue_work的代码，如下：

static void __queue_work(int cpu, struct workqueue_struct *wq,struct work_struct *work)
{struct pool_workqueue *pwq;struct worker_pool *last_pool;struct list_head *worklist;unsigned int work_flags;unsigned int req_cpu = cpu;/** While a work item is PENDING && off queue, a task trying to* steal the PENDING will busy-loop waiting for it to either get* queued or lose PENDING.  Grabbing PENDING and queueing should* happen with IRQ disabled.*/WARN_ON_ONCE(!irqs_disabled());debug_work_activate(work);/* if draining, only works from the same workqueue are allowed */if (unlikely(wq->flags & __WQ_DRAINING) &&WARN_ON_ONCE(!is_chained_work(wq)))return;
retry:if (req_cpu == WORK_CPU_UNBOUND)cpu = wq_select_unbound_cpu(raw_smp_processor_id());//根据传入的参数struct workqueue_struct *wq来选择需要的类型/* pwq which will be used unless @work is executing elsewhere */if (!(wq->flags & WQ_UNBOUND))pwq = per_cpu_ptr(wq->cpu_pwqs, cpu);----------------得到bound类型的pool_workqueue elsepwq = unbound_pwq_by_node(wq, cpu_to_node(cpu));-----得到unbound类型的pool_workqueue /** If @work was previously on a different pool, it might still be* running there, in which case the work needs to be queued on that* pool to guarantee non-reentrancy.*///work有可能已经存在另一个不同的work pool中，它可能仍旧在运行，为了避免重入，work仍然要加入到原来的work poollast_pool = get_work_pool(work);if (last_pool && last_pool != pwq->pool) {struct worker *worker;spin_lock(&last_pool->lock);worker = find_worker_executing_work(last_pool, work);if (worker && worker->current_pwq->wq == wq) {pwq = worker->current_pwq;----------------------得到last的pool_workqueue} else {/* meh... not running there, queue here */spin_unlock(&last_pool->lock);spin_lock(&pwq->pool->lock);}} else {spin_lock(&pwq->pool->lock);}/** pwq is determined and locked.  For unbound pools, we could have* raced with pwq release and it could already be dead.  If its* refcnt is zero, repeat pwq selection.  Note that pwqs never die* without another pwq replacing it in the numa_pwq_tbl or while* work items are executing on it, so the retrying is guaranteed to* make forward-progress.*/if (unlikely(!pwq->refcnt)) {if (wq->flags & WQ_UNBOUND) {spin_unlock(&pwq->pool->lock);cpu_relax();goto retry;}/* oops */WARN_ONCE(true, "workqueue: per-cpu pwq for %s on cpu%d has 0 refcnt",wq->name, cpu);}/* pwq determined, queue */trace_workqueue_queue_work(req_cpu, pwq, work);if (WARN_ON(!list_empty(&work->entry))) {spin_unlock(&pwq->pool->lock);return;}pwq->nr_in_flight[pwq->work_color]++;work_flags = work_color_to_flags(pwq->work_color);if (likely(pwq->nr_active < pwq->max_active)) {trace_workqueue_activate_work(work);pwq->nr_active++;worklist = &pwq->pool->worklist;----------------得到pool_workqueue的worker_pool的worklistif (list_empty(worklist))pwq->pool->watchdog_ts = jiffies;} else {work_flags |= WORK_STRUCT_DELAYED;worklist = &pwq->delayed_works;}insert_work(pwq, work, worklist, work_flags);-----把work加入到worklist，并唤醒spin_unlock(&pwq->pool->lock);
}

看函数insert_work代码：

static void insert_work(struct pool_workqueue *pwq, struct work_struct *work,struct list_head *head, unsigned int extra_flags)
{struct worker_pool *pool = pwq->pool;/* we own @work, set data and link */set_work_pwq(work, pwq, extra_flags);list_add_tail(&work->entry, head);---------------加入work pool的链表get_pwq(pwq);/** Ensure either wq_worker_sleeping() sees the above* list_add_tail() or we see zero nr_running to avoid workers lying* around lazily while there are works to be processed.*/smp_mb();if (__need_more_worker(pool))wake_up_worker(pool);----------------------唤醒work pool
}