On Tue, May 25, 2021 at 09:22:48AM +0200, Paolo Bonzini wrote: > On 24/05/21 16:59, Christoph Hellwig wrote: > > 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? > > There isn't an equivalent of the admin queue in virtio-blk, which would > allow the guest to configure the desired number of poll queues. The number > of queues is fixed. Dedicated vqs can be used for poll only, and I understand VM needn't to know if the vq is polled or driven by IRQ in VM. I tried that in v5.4, but not see obvious IOPS boost, so give up. https://github.com/ming1/linux/commits/my_v5.4-virtio-irq-poll Thanks, Ming
