Re: [Qemu-devel] [PATCH] virtio-net: do not start queues that are not enabled by the guest

[Jason Wang]

On 2019/2/13 下午10:51, Yuri Benditovich wrote:
> https://bugzilla.redhat.com/show_bug.cgi?id=1608226
> On startup/link-up in multiqueue configuration the virtio-net
> tries to starts all the queues, including those that the guest
> will not enable by VIRTIO_NET_CTRL_MQ_VQ_PAIRS_SET.
> If the guest driver does not allocate queues that it will not
> use (for example, Windows driver does not) and number of actually
> used queues is less that maximal number supported by the device,


Is this a requirement of e.g NDIS? If not, could we simply allocate all 
queues in this case. This is usually what normal Linux driver did.


> this causes vhost_net_start to fail and actually disables vhost
> for all the queues, reducing the performance.
> Current commit fixes this: initially only first queue is started,
> upon VIRTIO_NET_CTRL_MQ_VQ_PAIRS_SET started all the queues
> requested by the guest.
>
> Signed-off-by: Yuri Benditovich <address@hidden>
> ---
>   hw/net/virtio-net.c | 7 +++++--
>   1 file changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
> index 3f319ef723..d3b1ac6d3a 100644
> --- a/hw/net/virtio-net.c
> +++ b/hw/net/virtio-net.c
> @@ -174,7 +174,7 @@ static void virtio_net_vhost_status(VirtIONet *n, uint8_t 
> status)
>   {
>       VirtIODevice *vdev = VIRTIO_DEVICE(n);
>       NetClientState *nc = qemu_get_queue(n->nic);
> -    int queues = n->multiqueue ? n->max_queues : 1;
> +    int queues = n->multiqueue ? n->curr_queues : 1;
>   
>       if (!get_vhost_net(nc->peer)) {
>           return;
> @@ -1016,9 +1016,12 @@ static int virtio_net_handle_mq(VirtIONet *n, uint8_t 
> cmd,
>           return VIRTIO_NET_ERR;
>       }
>   
> -    n->curr_queues = queues;
>       /* stop the backend before changing the number of queues to avoid 
> handling a
>        * disabled queue */
> +    virtio_net_set_status(vdev, 0);


Any reason for doing this?

Thanks


> +
> +    n->curr_queues = queues;
> +
>       virtio_net_set_status(vdev, vdev->status);
>       virtio_net_set_queues(n);
>