On 05/30, Tejun Heo wrote:

This conversion is to make each vhost use a dedicated kthread so that
resource control via cgroup can be applied.

Personally, I agree. I think This is better than play with workqueue thread.

A couple of simple questions after the quick glance at the unapplied patch...

 void vhost_poll_flush(struct vhost_poll *poll)
 {
-	flush_work(&poll->work);
+	int seq = poll->queue_seq;
+
+	if (seq - poll->done_seq > 0)
+		wait_event(poll->done, seq - poll->done_seq <= 0);

The check before wait_event() is not needed, please note that wait_event()
checks the condition before __wait_event().

What I can't understand is why we do have ->queue_seq and ->done_seq.

Isn't the single "bool poll->active" enough? vhost_poll_queue() sets
->active == T, vhost_poller() clears it before wake_up_all(poll->done).

+static int vhost_poller(void *data)
+{
+	struct vhost_dev *dev = data;
+	struct vhost_poll *poll;
+
+repeat:
+	set_current_state(TASK_INTERRUPTIBLE);	/* mb paired w/ kthread_stop */

I don't understand the comment... why do we need this barrier?

+	if (kthread_should_stop()) {
+		__set_current_state(TASK_RUNNING);
+		return 0;
+	}
+
+	poll = NULL;
+	spin_lock(&dev->poller_lock);
+	if (!list_empty(&dev->poll_list)) {
+		poll = list_first_entry(&dev->poll_list,
+					struct vhost_poll, node);
+		list_del_init(&poll->node);
+	}
+	spin_unlock(&dev->poller_lock);
+
+	if (poll) {
+		__set_current_state(TASK_RUNNING);
+		poll->fn(poll);
+		smp_wmb();	/* paired with rmb in vhost_poll_flush() */
+		poll->done_seq = poll->queue_seq;
+		wake_up_all(&poll->done);
+	} else
+		schedule();
+
+	goto repeat;
+}

Given that vhost_poll_queue() does list_add() and wake_up_process() under
->poller_lock, I don't think we need any barriers to change ->state.

IOW, can't vhost_poller() simply do

	while(!kthread_should_stop()) {

		poll = NULL;
		spin_lock(&dev->poller_lock);
		if (!list_empty(&dev->poll_list)) {
			...
		} else
			 __set_current_state(TASK_INTERRUPTIBLE);
		spin_unlock(&dev->poller_lock);

		if (poll) {
			...
		} else
			schedule();
	}

?

Oleg.