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SubjectRe: [net-next rfc v7 2/3] virtio_net: multiqueue support
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On Monday, December 03, 2012 12:34:08 PM Rusty Russell wrote:
> Jason Wang <jasowang@redhat.com> writes:
> > +static const struct ethtool_ops virtnet_ethtool_ops;
> > +
> > +/*
> > + * Converting between virtqueue no. and kernel tx/rx queue no.
> > + * 0:rx0 1:tx0 2:cvq 3:rx1 4:tx1 ... 2N+1:rxN 2N+2:txN
> > + */
> > +static int vq2txq(struct virtqueue *vq)
> > +{
> > + int index = virtqueue_get_queue_index(vq);
> > + return index == 1 ? 0 : (index - 2) / 2;
> > +}
> > +
> > +static int txq2vq(int txq)
> > +{
> > + return txq ? 2 * txq + 2 : 1;
> > +}
> > +
> > +static int vq2rxq(struct virtqueue *vq)
> > +{
> > + int index = virtqueue_get_queue_index(vq);
> > + return index ? (index - 1) / 2 : 0;
> > +}
> > +
> > +static int rxq2vq(int rxq)
> > +{
> > + return rxq ? 2 * rxq + 1 : 0;
> > +}
> > +
>
> I thought MST changed the proposed spec to make the control queue always
> the last one, so this logic becomes trivial.

But it may break the support of legacy guest. If we boot a legacy single queue
guest on a 2 queue virtio-net device. It may think vq 2 is cvq which is indeed
rx1.
>
> > +static int virtnet_set_queues(struct virtnet_info *vi)
> > +{
> > + struct scatterlist sg;
> > + struct virtio_net_ctrl_rfs s;
> > + struct net_device *dev = vi->dev;
> > +
> > + s.virtqueue_pairs = vi->curr_queue_pairs;
> > + sg_init_one(&sg, &s, sizeof(s));
> > +
> > + if (!vi->has_cvq)
> > + return -EINVAL;
> > +
> > + if (!virtnet_send_command(vi, VIRTIO_NET_CTRL_RFS,
> > + VIRTIO_NET_CTRL_RFS_VQ_PAIRS_SET, &sg, 1, 0)){
> > + dev_warn(&dev->dev, "Fail to set the number of queue pairs to"
> > + " %d\n", vi->curr_queue_pairs);
> > + return -EINVAL;
> > + }
>
> Where do we check the VIRTIO_NET_F_RFS bit?

Yes, we need this check. Will let the caller does the check and add a comment
and check in the caller.
>
> > static int virtnet_probe(struct virtio_device *vdev)
> > {
> >
> > - int err;
> > + int i, err;
> >
> > struct net_device *dev;
> > struct virtnet_info *vi;
> >
> > + u16 curr_queue_pairs;
> > +
> > + /* Find if host supports multiqueue virtio_net device */
> > + err = virtio_config_val(vdev, VIRTIO_NET_F_RFS,
> > + offsetof(struct virtio_net_config,
> > + max_virtqueue_pairs), &curr_queue_pairs);
> > +
> > + /* We need at least 2 queue's */
> > + if (err)
> > + curr_queue_pairs = 1;
>
> Huh? Just call this queue_pairs. It's not curr_ at all...
>
> > + if (virtio_has_feature(vdev, VIRTIO_NET_F_CTRL_VQ))
> > + vi->has_cvq = true;
> > +
> > + /* Use single tx/rx queue pair as default */
> > + vi->curr_queue_pairs = 1;
> > + vi->max_queue_pairs = curr_queue_pairs;
>
> See...

Right, will use max_queue_pairs then.

Thanks
>
> Cheers,
> Rusty.
> --
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