Re: [Qemu-devel] [PATCH] virtio-net: remove virtio queues if the guest doesn't support multiqueue

[Jason Wang <jasowang@redhat.com>]

On 07/15/2015 02:23 PM, Wen Congyang wrote:
> commit da51a335 adds all queues in .realize(). But if the
> guest doesn't support multiqueue, we forget to remove them. And
> we cannot handle the ctrl vq corretly. The guest will hang.
>
> Signed-off-by: Wen Congyang <wency@cn.fujitsu.com>

Thanks for the patch, some questions, see below.

> ---
>  hw/net/virtio-net.c | 69 +++++++++++++++++++++++++++++++++++++++++------------
>  1 file changed, 54 insertions(+), 15 deletions(-)
>
> diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
> index e3c2db3..658806a 100644
> --- a/hw/net/virtio-net.c
> +++ b/hw/net/virtio-net.c
> @@ -1306,9 +1306,62 @@ static void virtio_net_tx_bh(void *opaque)
>      }
>  }
>  
> +static void virtio_net_add_queue(VirtIONet *n, int index)
> +{
> +    VirtIODevice *vdev = VIRTIO_DEVICE(n);
> +
> +    n->vqs[index].rx_vq = virtio_add_queue(vdev, 256, virtio_net_handle_rx);
> +    if (n->net_conf.tx && !strcmp(n->net_conf.tx, "timer")) {
> +        n->vqs[index].tx_vq =
> +            virtio_add_queue(vdev, 256, virtio_net_handle_tx_timer);
> +        n->vqs[index].tx_timer = timer_new_ns(QEMU_CLOCK_VIRTUAL,
> +                                              virtio_net_tx_timer,
> +                                              &n->vqs[index]);
> +    } else {
> +        n->vqs[index].tx_vq =
> +            virtio_add_queue(vdev, 256, virtio_net_handle_tx_bh);
> +        n->vqs[index].tx_bh = qemu_bh_new(virtio_net_tx_bh, &n->vqs[index]);
> +    }
> +
> +    n->vqs[index].tx_waiting = 0;
> +    n->vqs[index].n = n;
> +}
> +
> +static void virtio_net_change_num_queues(VirtIONet *n, int new_max_queues)
> +{
> +    VirtIODevice *vdev = VIRTIO_DEVICE(n);
> +    int old_num_queues = virtio_get_num_queues(vdev);
> +    int new_num_queues = new_max_queues * 2 + 1;
> +    int i;
> +
> +    assert(old_num_queues >= 3);
> +    assert(old_num_queues % 2 == 1);
> +
> +    if (old_num_queues == new_num_queues) {
> +        return;
> +    }
> +
> +    /* Remove ctrl_vq first */
> +    virtio_del_queue(vdev, old_num_queues - 1);

Why ctrl vq must be first to be deleted?

> +
> +    for (i = new_num_queues - 1; i < old_num_queues - 1; i++) {
> +        virtio_del_queue(vdev, i);

Do we need to delete bh and timer also here?

> +    }
> +
> +    for (i = old_num_queues - 1; i < new_num_queues - 1; i += 2) {
> +        virtio_net_add_queue(n, i / 2);
> +    }
> +
> +    /* add ctrl_vq last */
> +    n->ctrl_vq = virtio_add_queue(vdev, 64, virtio_net_handle_ctrl);
> +}
> +
>  static void virtio_net_set_multiqueue(VirtIONet *n, int multiqueue)
>  {
> +    int max = multiqueue ? n->max_queues : 1;
> +
>      n->multiqueue = multiqueue;
> +    virtio_net_change_num_queues(n, max);
>  
>      virtio_net_set_queues(n);
>  }
> @@ -1583,21 +1636,7 @@ static void virtio_net_device_realize(DeviceState *dev, Error **errp)
>      }
>  
>      for (i = 0; i < n->max_queues; i++) {
> -        n->vqs[i].rx_vq = virtio_add_queue(vdev, 256, virtio_net_handle_rx);
> -        if (n->net_conf.tx && !strcmp(n->net_conf.tx, "timer")) {
> -            n->vqs[i].tx_vq =
> -                virtio_add_queue(vdev, 256, virtio_net_handle_tx_timer);
> -            n->vqs[i].tx_timer = timer_new_ns(QEMU_CLOCK_VIRTUAL,
> -                                              virtio_net_tx_timer,
> -                                              &n->vqs[i]);
> -        } else {
> -            n->vqs[i].tx_vq =
> -                virtio_add_queue(vdev, 256, virtio_net_handle_tx_bh);
> -            n->vqs[i].tx_bh = qemu_bh_new(virtio_net_tx_bh, &n->vqs[i]);
> -        }
> -
> -        n->vqs[i].tx_waiting = 0;
> -        n->vqs[i].n = n;
> +        virtio_net_add_queue(n, i);
>      }
>  
>      n->ctrl_vq = virtio_add_queue(vdev, 64, virtio_net_handle_ctrl);