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

[Michael S. Tsirkin]

On Wed, Aug 11, 2021 at 08:20:03PM -0500, ivan wrote:
> 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.

OK so that's

Tested-by: ivan <ivan@xxxxxxxxxxxxxxxxxxxxxxxxxx>

It is still weird that without the patch networking dies.

What happens if you apply the patch then try to disable GRO
using ethtool?

-- 
MST