Re: [PATCH v2 1/3] virtio_ring: Allow non power of 2 sizes for packed virtqueue

[David Edmondson <david.edmondson@oracle.com>]

Feng Liu <feliu@nvidia.com> writes:

> According to the Virtio Specification, the Queue Size parameter of a
> virtqueue corresponds to the maximum number of descriptors in that
> queue, and it does not have to be a power of 2 for packed virtqueues.
> However, the virtio_pci_modern driver enforced a power of 2 check for
> virtqueue sizes, which is unnecessary and restrictive for packed
> virtuqueue.
>
> Split virtqueue still needs to check the virtqueue size is power_of_2
> which has been done in vring_alloc_queue_split of the virtio_ring layer.
>
> To validate this change, we tested various virtqueue sizes for packed
> rings, including 128, 256, 512, 100, 200, 500, and 1000, with
> CONFIG_PAGE_POISONING enabled, and all tests passed successfully.
>
> Signed-off-by: Feng Liu <feliu@nvidia.com>
> Reviewed-by: Jiri Pirko <jiri@nvidia.com>
>

Reviewed-by: David Edmondson <david.edmondson@oracle.com>

> ---
> v0 -> v1
> feedbacks from Jason Wang and Michael S. Tsirkin
> - remove power_of_2 check of virtqueue size
>
> v1 -> v2
> feedbacks from Parav Pandit and Jiri Pirko
> - keep power_of_2 check of split virtqueue in vring_alloc_queue_split of
>   virtio_ring layer.
> ---
>  drivers/virtio/virtio_pci_modern.c | 5 -----
>  1 file changed, 5 deletions(-)
>
> diff --git a/drivers/virtio/virtio_pci_modern.c b/drivers/virtio/virtio_pci_modern.c
> index 9e496e288cfa..6e713904d8e8 100644
> --- a/drivers/virtio/virtio_pci_modern.c
> +++ b/drivers/virtio/virtio_pci_modern.c
> @@ -310,11 +310,6 @@ static struct virtqueue *setup_vq(struct virtio_pci_device *vp_dev,
>  	if (!num || vp_modern_get_queue_enable(mdev, index))
>  		return ERR_PTR(-ENOENT);
>  
> -	if (!is_power_of_2(num)) {
> -		dev_warn(&vp_dev->pci_dev->dev, "bad queue size %u", num);
> -		return ERR_PTR(-EINVAL);
> -	}
> -
>  	info->msix_vector = msix_vec;
>  
>  	/* create the vring */
> -- 
> 2.34.1
-- 
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