Re: [Qemu-devel] [PATCH] virtio-net: calculate proper msix vectors on init

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

On Fri, Feb 21, 2014 at 01:00:57PM +0800, Jason Wang wrote:
> Currently, the default msix vectors for virtio-net-pci is 3 which is
> obvious not suitable for multiqueue guest, so we depends on the user
> or management tools to pass a correct vectors parameter. In fact, we
> can simplifying this by calculate the number of vectors on init.
> 
> Consider we have N queues, the number of vectors needed is 2*N + 2
> (plus one config interrupt and control vq). We didn't check whether or
> not host support control vq because it was added unconditionally by
> qemu to avoid breaking legacy guests such as Minix.
> 
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Michael S. Tsirkin <mst@redhat.com>
> Signed-off-by: Jason Wang <jasowang@redhat.com>
> ---
>  hw/virtio/virtio-pci.c | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c
> index 7b91841..1dec491 100644
> --- a/hw/virtio/virtio-pci.c
> +++ b/hw/virtio/virtio-pci.c
> @@ -1416,7 +1416,8 @@ static const TypeInfo virtio_serial_pci_info = {
>  static Property virtio_net_properties[] = {
>      DEFINE_PROP_BIT("ioeventfd", VirtIOPCIProxy, flags,
>                      VIRTIO_PCI_FLAG_USE_IOEVENTFD_BIT, false),
> -    DEFINE_PROP_UINT32("vectors", VirtIOPCIProxy, nvectors, 3),
> +    DEFINE_PROP_UINT32("vectors", VirtIOPCIProxy, nvectors,
> +                       DEV_NVECTORS_UNSPECIFIED),
>      DEFINE_VIRTIO_NET_FEATURES(VirtIOPCIProxy, host_features),
>      DEFINE_NIC_PROPERTIES(VirtIONetPCI, vdev.nic_conf),
>      DEFINE_VIRTIO_NET_PROPERTIES(VirtIONetPCI, vdev.net_conf),
> @@ -1428,6 +1429,13 @@ static int virtio_net_pci_init(VirtIOPCIProxy *vpci_dev)
>      DeviceState *qdev = DEVICE(vpci_dev);
>      VirtIONetPCI *dev = VIRTIO_NET_PCI(vpci_dev);
>      DeviceState *vdev = DEVICE(&dev->vdev);
> +    VirtIONet *net = VIRTIO_NET(&dev->vdev);
> +
> +    if (vpci_dev->nvectors == DEV_NVECTORS_UNSPECIFIED) {
> +        vpci_dev->nvectors = 2 * MAX(net->nic_conf.queues, 1) + 2;
> +    }
> +
> +    fprintf(stderr, "vectors is %d\n", vpci_dev->nvectors);

last lin shouldn't be there obviously.

>  
>      virtio_net_set_config_size(&dev->vdev, vpci_dev->host_features);
>      virtio_net_set_netclient_name(&dev->vdev, qdev->id,
> -- 
> 1.8.3.2