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

[ivan]

On Thu, Aug 12, 2021 at 12:00 AM Michael S. Tsirkin <mst@xxxxxxxxxx> wrote:
>
> 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?
Nothing bad.  Ethtool shows successful change to off.
Makes no differrece on the iperf tests.  Still good.