Subject: Re: [PATCH 2/2] virtio-net: ethtool configurable RXCSUM

From: "Michael S. Tsirkin" <[email-masked]>
Date: Tue, 29 Sep 2020 01:55:13 -0400

On Tue, Sep 29, 2020 at 09:45:24AM +0800, Tonghao Zhang wrote:
> On Tue, Sep 29, 2020 at 3:25 AM Michael S. Tsirkin <[email-masked]> wrote:
> >
> > On Mon, Sep 28, 2020 at 11:39:15AM +0800, [email-masked] wrote:
> > > From: Tonghao Zhang <[email-masked]>
> > >
> > > Allow user configuring RXCSUM separately with ethtool -K,
> > > reusing the existing virtnet_set_guest_offloads helper
> > > that configures RXCSUM for XDP. This is conditional on
> > > VIRTIO_NET_F_CTRL_GUEST_OFFLOADS.
> > >
> > > Cc: Michael S. Tsirkin <[email-masked]>
> > > Cc: Jason Wang <[email-masked]>
> > > Signed-off-by: Tonghao Zhang <[email-masked]>
> > > ---
> > >  drivers/net/virtio_net.c | 40 ++++++++++++++++++++++++++++------------
> > >  1 file changed, 28 insertions(+), 12 deletions(-)
> > >
> > > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > > index 21b71148c532..2e3af0b2c281 100644
> > > --- a/drivers/net/virtio_net.c
> > > +++ b/drivers/net/virtio_net.c
> > > @@ -68,6 +68,8 @@ static const unsigned long guest_offloads[] = {
> > >                               (1ULL << VIRTIO_NET_F_GUEST_ECN)  | \
> > >                               (1ULL << VIRTIO_NET_F_GUEST_UFO))
> > >
> > > +#define GUEST_OFFLOAD_CSUM_MASK (1ULL << VIRTIO_NET_F_GUEST_CSUM)
> > > +
> > >  struct virtnet_stat_desc {
> > >       char desc[ETH_GSTRING_LEN];
> > >       size_t offset;
> > > @@ -2526,25 +2528,37 @@ static int virtnet_set_features(struct net_device *dev,
> > >                               netdev_features_t features)
> > >  {
> > >       struct virtnet_info *vi = netdev_priv(dev);
> > > -     u64 offloads;
> > > +     u64 offloads = vi->guest_offloads &
> > > +                    vi->guest_offloads_capable;
> > >       int err;
> > >
> > > -     if ((dev->features ^ features) & NETIF_F_LRO) {
> > > -             if (vi->xdp_queue_pairs)
> > > -                     return -EBUSY;
> > > +     /* Don't allow configuration while XDP is active. */
> > > +     if (vi->xdp_queue_pairs)
> > > +             return -EBUSY;
> > >
> > > +     if ((dev->features ^ features) & NETIF_F_LRO) {
> > >               if (features & NETIF_F_LRO)
> > > -                     offloads = vi->guest_offloads_capable;
> > > +                     offloads |= GUEST_OFFLOAD_LRO_MASK;
> > >               else
> > > -                     offloads = vi->guest_offloads_capable &
> > > -                                ~GUEST_OFFLOAD_LRO_MASK;
> > > +                     offloads &= ~GUEST_OFFLOAD_LRO_MASK;
> > > +     }
> > >
> > > -             err = virtnet_set_guest_offloads(vi, offloads);
> > > -             if (err)
> > > -                     return err;
> > > -             vi->guest_offloads = offloads;
> > > +     if ((dev->features ^ features) & NETIF_F_RXCSUM) {
> > > +             if (features & NETIF_F_RXCSUM)
> > > +                     offloads |= GUEST_OFFLOAD_CSUM_MASK;
> > > +             else
> > > +                     offloads &= ~GUEST_OFFLOAD_CSUM_MASK;
> > >       }
> > >
> > > +     if (offloads == (vi->guest_offloads &
> > > +                      vi->guest_offloads_capable))
> > > +             return 0;
> >
> > Hmm, what exactly does this do?
> If the features(lro, rxcsum) we supported, are not changed, it is not
> necessary to invoke virtnet_set_guest_offloads.

okay, could you describe the cases where this triggers in a bit more
detail pls?

> > > +
> > > +     err = virtnet_set_guest_offloads(vi, offloads);
> > > +     if (err)
> > > +             return err;
> > > +
> > > +     vi->guest_offloads = offloads;
> > >       return 0;
> > >  }
> > >
> > > @@ -3013,8 +3027,10 @@ static int virtnet_probe(struct virtio_device *vdev)
> > >       if (virtio_has_feature(vdev, VIRTIO_NET_F_GUEST_TSO4) ||
> > >           virtio_has_feature(vdev, VIRTIO_NET_F_GUEST_TSO6))
> > >               dev->features |= NETIF_F_LRO;
> > > -     if (virtio_has_feature(vdev, VIRTIO_NET_F_CTRL_GUEST_OFFLOADS))
> > > +     if (virtio_has_feature(vdev, VIRTIO_NET_F_CTRL_GUEST_OFFLOADS)) {
> > > +             dev->hw_features |= NETIF_F_RXCSUM;
> > >               dev->hw_features |= NETIF_F_LRO;
> > > +     }
> > >
> > >       dev->vlan_features = dev->features;
> > >
> > > --
> > > 2.23.0
> >
> 
> 
> -- 
> Best regards, Tonghao