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Date: Tue, 17 Aug 2021 02:45:54 -0400
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Jason Wang <jasowang@...hat.com>
Cc: davem@...emloft.net, kuba@...nel.org, willemb@...gle.com,
virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
linux-kernel@...r.kernel.org, ivan@...stigetransportation.com,
xiangxia.m.yue@...il.com
Subject: Re: [PATCH net] virtio-net: use NETIF_F_GRO_HW instead of NETIF_F_LRO
Patch is good. Suggest some tweaks to the commit log.
On Tue, Aug 17, 2021 at 10:03:38AM +0800, Jason Wang wrote:
> Commit a02e8964eaf92 ("virtio-net: ethtool configurable LRO") tries to
> advertise LRO on behalf of the guest offloading features and allow the
tries to advertise -> advertises
that part actually works.
allow -> allows
on behalf of features is really weird. maybe "maps"?
> administrator to enable and disable those features via ethtool.
>
> This may lead several issues:
may lead->lead to
>
> - For the device that doesn't support control guest offloads, the
> "LRO" can't be disabled so we will get a warn in the
warn -> warning
> dev_disable_lro()
.. when turning off LRO or when enabling forwarding bridging etc.
> - For the device that have the control guest offloads, the guest
have the -> supports
> offloads were disabled in the case of bridge etc
etc -> forwarding etc
> which may slow down
were -> are
may slow -> slows
> the traffic.
>
> Fixing this by using NETIF_F_GRO_HW instead. Though the spec does not
> guaranteed to be re-segmented as original explicitly now, we can add
guaranteed -> guarantee
> that to the spec
I would add:
Further, we never advertised LRO historically before a02e8964eaf92
("virtio-net: ethtool configurable LRO") and so bridged/forwarded
configs effectively relied on virtio receive offloads being GRO.
> and then we can catch the bad configuration and
> setup.
Don't know what does this part mean. How would we catch it?
With a new flag? Let's say so.
>
> Fixes: a02e8964eaf92 ("virtio-net: ethtool configurable LRO")
> Signed-off-by: Jason Wang <jasowang@...hat.com>
Proposed rewritten commit log:
===
[PATCH net] virtio-net: use NETIF_F_GRO_HW instead of NETIF_F_LRO
Commit a02e8964eaf92 ("virtio-net: ethtool configurable LRO")
maps LRO to virtio guest offloading features and allows the
administrator to enable and disable those features via ethtool.
This leads to several issues:
- For a device that doesn't support control guest offloads, the "LRO"
can't be disabled triggering WARN in dev_disable_lro() when turning
off LRO or when enabling forwarding bridging etc.
- For a device that supports control guest offloads, the guest
offloads are disabled in cases of bridging, forwarding etc
slowing down the traffic.
Fix this by using NETIF_F_GRO_HW instead. Though the spec does not
guarantee packets to be re-segmented as the original ones,
we can add that to the spec, possibly with a flag for devices to
differentiate between GRO and LRO.
Further, we never advertised LRO historically before a02e8964eaf92
("virtio-net: ethtool configurable LRO") and so bridged/forwarded
configs effectively always relied on virtio receive offloads behaving
like GRO - thus even if this breaks any configs it is at least not
a regression.
Fixes: a02e8964eaf92 ("virtio-net: ethtool configurable LRO")
Acked-by: Michael S. Tsirkin <mst@...hat.com>
Reported-by: Ivan <ivan@...stigetransportation.com>
Tested-by: Ivan <ivan@...stigetransportation.com>
Signed-off-by: Jason Wang <jasowang@...hat.com>
===
> ---
> 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;
>
> --
> 2.25.1
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