[workqueue]笔记

原创已于 2024-03-16 20:35:26 修改 · 938 阅读

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#linux #android

于 2024-03-16 20:34:35 首次发布

文章讨论了在特定CPU上将工作加入工作队列（queue_work_on）的方法，以及当工作队列活跃任务数接近最大值时如何处理新工作的插入。它涉及工作结构的工作状态管理和线程池的容量控制。

疑问1：继续Queue同一个work能成功加入worker_pool->worklist吗？

/**
 * queue_work_on - queue work on specific cpu
 * @cpu: CPU number to execute work on
 * @wq: workqueue to use
 * @work: work to queue
 *
 * We queue the work to a specific CPU, the caller must ensure it
 * can't go away.  Callers that fail to ensure that the specified
 * CPU cannot go away will execute on a randomly chosen CPU.
 *
 * Return: %false if @work was already on a queue, %true otherwise.
 */
bool queue_work_on(int cpu, struct workqueue_struct *wq,
		   struct work_struct *work)
{
	bool ret = false;
	unsigned long flags;

	local_irq_save(flags);//关闭本地中断，防止work的data并发设置

	if (!test_and_set_bit(WORK_STRUCT_PENDING_BIT, work_data_bits(work))) {
		__queue_work(cpu, wq, work);//WORK_STRUCT_PENDING_BIT表示任务已经在处理了，完成之前不能重复提交。
		ret = true;
	}

	local_irq_restore(flags);//打开本地中断
	return ret;
}
EXPORT_SYMBOL(queue_work_on);

疑问2：假设pwq->nr_active >= max_active 时；还能继续insert work成功吗？

1425  static void __queue_work(int cpu, struct workqueue_struct *wq,
1426  			 struct work_struct *work)
1427  {
1428  	struct pool_workqueue *pwq;
1429  	struct worker_pool *last_pool;
1430  	struct list_head *worklist;
1431  	unsigned int work_flags;
1432  	unsigned int req_cpu = cpu;
1433  
1434  	/*
1435  	 * While a work item is PENDING && off queue, a task trying to
1436  	 * steal the PENDING will busy-loop waiting for it to either get
1437  	 * queued or lose PENDING.  Grabbing PENDING and queueing should
1438  	 * happen with IRQ disabled.
1439  	 */
1440  	lockdep_assert_irqs_disabled();

…… ……

1503  	/* pwq determined, queue */
1504  	trace_workqueue_queue_work(req_cpu, pwq, work);
1505  
1506  	if (WARN_ON(!list_empty(&work->entry)))
1507  		goto out;
1508  
1509  	pwq->nr_in_flight[pwq->work_color]++;
1510  	work_flags = work_color_to_flags(pwq->work_color);
1511  
1512  	if (likely(pwq->nr_active < pwq->max_active)) {
1513  		trace_workqueue_activate_work(work);
1514  		pwq->nr_active++;
1515  		worklist = &pwq->pool->worklist;
1516  		if (list_empty(worklist))
1517  			pwq->pool->watchdog_ts = jiffies;
1518  	} else {
1519  		work_flags |= WORK_STRUCT_INACTIVE;
1520  		worklist = &pwq->inactive_works;
1521  	}
1522  
1523  	debug_work_activate(work);
1524  	insert_work(pwq, work, worklist, work_flags);
1525  
1526  out:
1527  	raw_spin_unlock(&pwq->pool->lock);
1528  	rcu_read_unlock();
1529  }2