Re: [PATCH] virtio-fs: fix MSI-X nvectors calculation

["Michael S. Tsirkin" <mst@redhat.com>]

On Mon, Dec 09, 2019 at 11:07:59AM +0000, Stefan Hajnoczi wrote:
> The following MSI-X vectors are required:
>  * VIRTIO Configuration Change
>  * hiprio virtqueue
>  * requests virtqueues
> 
> Fix the calculation to reserve enough MSI-X vectors.  Otherwise guest
> drivers fall back to a sub-optional configuration where all virtqueues
> share a single vector.
> 
> This change does not break live migration compatibility since
> vhost-user-fs-pci devices are not migratable yet.
> 
> Reported-by: Vivek Goyal <vgoyal@redhat.com>
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

Reviewed-by: Michael S. Tsirkin <mst@redhat.com>


> ---
>  hw/virtio/vhost-user-fs-pci.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/virtio/vhost-user-fs-pci.c b/hw/virtio/vhost-user-fs-pci.c
> index 933a3f265b..e3a649d4a6 100644
> --- a/hw/virtio/vhost-user-fs-pci.c
> +++ b/hw/virtio/vhost-user-fs-pci.c
> @@ -40,7 +40,8 @@ static void vhost_user_fs_pci_realize(VirtIOPCIProxy *vpci_dev, Error **errp)
>      DeviceState *vdev = DEVICE(&dev->vdev);
>  
>      if (vpci_dev->nvectors == DEV_NVECTORS_UNSPECIFIED) {
> -        vpci_dev->nvectors = dev->vdev.conf.num_request_queues + 1;
> +        /* Also reserve config change and hiprio queue vectors */
> +        vpci_dev->nvectors = dev->vdev.conf.num_request_queues + 2;
>      }
>  
>      qdev_set_parent_bus(vdev, BUS(&vpci_dev->bus));
> -- 
> 2.23.0