Re: [RFC PATCH] virtio-net: use NETIF_F_GRO_HW instead of NETIF_F_LRO

[ivan]

On Wed, Aug 11, 2021 at 3:16 AM Jason Wang <jasowang@xxxxxxxxxx> wrote:
>
> Commit a02e8964eaf92 ("virtio-net: ethtool configurable LRO") tries to
> advertise LRO on behalf of the guest offloading features and allow the
> administrator to enable and disable those features via ethtool.
>
> This may lead several issues:
>
> - For the device that doesn't support control guest offloads, the
>   "LRO" can't be disabled so we will get a warn in the
>   dev_disable_lro()
> - For the device that have the control guest offloads, the guest
>   offloads were disabled in the case of bridge etc which may slow down
>   the traffic.
>
> Try to fix this by using NETIF_F_GRO_HW instead so we're not
> guaranteed to be re-segmented as original. Or we may want a new netdev
> feature like RX_GSO since the guest offloads for virtio-net is
> actually to receive GSO packet.
>
> Or we can try not advertise LRO is control guest offloads is not
> enabled. This solves the warning but will still slow down the traffic.
>
> Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx>
> ---
>  drivers/net/virtio_net.c | 14 +++++++-------
>  1 file changed, 7 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 0416a7e00914..10c382b08bce 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -63,7 +63,7 @@ static const unsigned long guest_offloads[] = {
>         VIRTIO_NET_F_GUEST_CSUM
>  };
>
> -#define GUEST_OFFLOAD_LRO_MASK ((1ULL << VIRTIO_NET_F_GUEST_TSO4) | \
> +#define GUEST_OFFLOAD_GRO_HW_MASK ((1ULL << VIRTIO_NET_F_GUEST_TSO4) | \
>                                 (1ULL << VIRTIO_NET_F_GUEST_TSO6) | \
>                                 (1ULL << VIRTIO_NET_F_GUEST_ECN)  | \
>                                 (1ULL << VIRTIO_NET_F_GUEST_UFO))
> @@ -2481,7 +2481,7 @@ static int virtnet_xdp_set(struct net_device *dev, struct bpf_prog *prog,
>                 virtio_has_feature(vi->vdev, VIRTIO_NET_F_GUEST_ECN) ||
>                 virtio_has_feature(vi->vdev, VIRTIO_NET_F_GUEST_UFO) ||
>                 virtio_has_feature(vi->vdev, VIRTIO_NET_F_GUEST_CSUM))) {
> -               NL_SET_ERR_MSG_MOD(extack, "Can't set XDP while host is implementing LRO/CSUM, disable LRO/CSUM first");
> +               NL_SET_ERR_MSG_MOD(extack, "Can't set XDP while host is implementing GRO_HW/CSUM, disable GRO_HW/CSUM first");
>                 return -EOPNOTSUPP;
>         }
>
> @@ -2612,15 +2612,15 @@ static int virtnet_set_features(struct net_device *dev,
>         u64 offloads;
>         int err;
>
> -       if ((dev->features ^ features) & NETIF_F_LRO) {
> +       if ((dev->features ^ features) & NETIF_F_GRO_HW) {
>                 if (vi->xdp_enabled)
>                         return -EBUSY;
>
> -               if (features & NETIF_F_LRO)
> +               if (features & NETIF_F_GRO_HW)
>                         offloads = vi->guest_offloads_capable;
>                 else
>                         offloads = vi->guest_offloads_capable &
> -                                  ~GUEST_OFFLOAD_LRO_MASK;
> +                                  ~GUEST_OFFLOAD_GRO_HW_MASK;
>
>                 err = virtnet_set_guest_offloads(vi, offloads);
>                 if (err)
> @@ -3100,9 +3100,9 @@ static int virtnet_probe(struct virtio_device *vdev)
>                 dev->features |= NETIF_F_RXCSUM;
>         if (virtio_has_feature(vdev, VIRTIO_NET_F_GUEST_TSO4) ||
>             virtio_has_feature(vdev, VIRTIO_NET_F_GUEST_TSO6))
> -               dev->features |= NETIF_F_LRO;
> +               dev->features |= NETIF_F_GRO_HW;
>         if (virtio_has_feature(vdev, VIRTIO_NET_F_CTRL_GUEST_OFFLOADS))
> -               dev->hw_features |= NETIF_F_LRO;
> +               dev->hw_features |= NETIF_F_GRO_HW;
>
>         dev->vlan_features = dev->features;
>
> --

I applied this patch, recompiled the kernel, and tested it.
The warning messages are gone. Network speed is normal.
I can now enable forwarding, and nothing bad happens.
So far, so good.

Thank you.