Re: [PATCH 1/3] vhost: replace vhost_workqueue with per-vhost kthread

On 05/31, Tejun Heo wrote:

On 05/31/2010 04:39 PM, Oleg Nesterov wrote:

quoted

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).

I might have slightly over engineered this part not knowing the
expected workload.  ->queue_seq/->done_seq pair is to guarantee that
flushers never get starved.

Ah, indeed.

Well, afaics we do not need 2 counters anyway, both vhost_poll_queue()
and vhost_poller() could increment the single counter and the flusher
can take bit 0 into account. But I agree 2 counters are much more clean.

quoted

quoted

+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?

So that either kthread_stop()'s should_stop = 1 in kthread_stop() is
visible to kthread_should_stop() or task state is set to RUNNING.

Of course, you are right. I am really surprized I asked this question ;)

Thanks,

Oleg.