Re: [PATCH 3/3] virtio_blk: implement blk_mq_ops->poll()

[Christoph Hellwig]

On Thu, May 20, 2021 at 03:13:05PM +0100, Stefan Hajnoczi wrote:
> Possible drawbacks of this approach:
> 
> - Hardware virtio_blk implementations may find virtqueue_disable_cb()
>   expensive since it requires DMA. If such devices become popular then
>   the virtio_blk driver could use a similar approach to NVMe when
>   VIRTIO_F_ACCESS_PLATFORM is detected in the future.
> 
> - If a blk_poll() thread is descheduled it not only hurts polling
>   performance but also delays completion of non-REQ_HIPRI requests on
>   that virtqueue since vq notifications are disabled.

Yes, I think this is a dangerous configuration.  What argument exists
again just using dedicated poll queues?