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SubjectRe: [PATCH v4 2/2] virtio_balloon: Use a workqueue instead of "vballoon" kthread
Hello,

On Fri, Jan 01, 2016 at 12:18:17PM +0200, Michael S. Tsirkin wrote:
> > My initial idea was to use a dedicated workqueue. Michael S. Tsirkin
> > suggested using a system one. Tejun Heo confirmed that the system
> > workqueue has a pretty high concurrency level (256) by default.
> > Therefore we need not be afraid of too long blocking.
>
> Right but fill has a 1/5 second sleep on failure - *that*
> is problematic for a system queue.

Why so? As long as the maximum concurrently used workers are not
high, 1/5 second or even a lot longer sleeps are completely fine.

> > @@ -563,7 +534,7 @@ static void virtballoon_remove(struct virtio_device *vdev)
> > struct virtio_balloon *vb = vdev->priv;
> >
> > unregister_oom_notifier(&vb->nb);
> > - kthread_stop(vb->thread);
> > + cancel_work_sync(&vb->wq_work);
>
> OK but since job requeues itself, cancelling like this might not be enough.

As long as there's no further external queueing, cancel_work_sync() is
guaranteed to kill a self-requeueing work item.

Thanks.

--
tejun


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