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

From: "Michael S. Tsirkin" <[email-masked]>
Date: Tue, 29 Sep 2020 03:25:08 -0400

On Tue, Sep 29, 2020 at 03:17:50PM +0800, Tonghao Zhang wrote:
> On Tue, Sep 29, 2020 at 2:22 PM Michael S. Tsirkin <[email-masked]> wrote:
> >
> > On Tue, Sep 29, 2020 at 02:10:56PM +0800, Tonghao Zhang wrote:
> > > On Tue, Sep 29, 2020 at 1:55 PM Michael S. Tsirkin <[email-masked]> wrote:
> > > >
> > > > 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?
> > > Hi
> > > As I known,  when we run che commands show as below:
> > > ethtool -K eth1 sg off
> > > ethtool -K eth1 tso off
> > >
> > > In that case, we will not invoke virtnet_set_guest_offloads.
> >
> > How about initialization though? E.g. it looks like guest_offloads
> > is 0-initialized, won't this skip the first command to disable
> > offloads?
> I guest you mean that: if guest_offloads == 0, and run the command
> "ethtool -K eth1 sg off", that will disable offload ?
> In that patch
> u64 offloads = vi->guest_offloads & vi->guest_offloads_capable; // offload = 0
> .....
>  if (offloads == (vi->guest_offloads & vi->guest_offloads_capable)) //
> if offload not changed, offload == 0, and (vi->guest_offloads &
> vi->guest_offloads_capable) == 0.
>         return 0;
> 
> virtnet_set_guest_offloads // that will not be invoked, so will not
> disable offload

Sorry don't understand the question here.
At device init offloads are enabled, I am asking won't this skip
disabling them the first time this function is invoked.
Why are we bothering with this check? Is this called lots of
times where offloads are unchanged to make skipping the
command worthwhile?

> > > > > > > +
> > > > > > > +     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
> > > >
> > >
> > >
> > > --
> > > Best regards, Tonghao
> >
> 
> 
> -- 
> Best regards, Tonghao