veth: implement ndo_set_rx_headroom

The rx headroom for veth dev is the peer device needed_headroom.
Avoid ping-pong updates setting the private flag IFF_PHONY_HEADROOM.

This avoids skb head reallocation when forwarding from a veth dev
towards a device adding some kind of encapsulation.

When transmitting frames below the MTU size towards a vxlan device,
this gives about 10% performance speed-up when OVS is used to connect
the veth and the vxlan device and a little more when using a
plain Linux bridge.

Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/drivers/net/veth.c b/drivers/net/veth.c
index ba21d07..4f30a6a 100644 (file)
--- a/drivers/net/veth.c
+++ b/drivers/net/veth.c
@@ -35,6 +35,7 @@ struct pcpu_vstats {
 struct veth_priv {
        struct net_device __rcu *peer;
        atomic64_t              dropped;
+       unsigned                requested_headroom;
 };
 
 /*
@@ -271,6 +272,29 @@ static int veth_get_iflink(const struct net_device *dev)
        return iflink;
 }
 
+static void veth_set_rx_headroom(struct net_device *dev, int new_hr)
+{
+       struct veth_priv *peer_priv, *priv = netdev_priv(dev);
+       struct net_device *peer;
+
+       if (new_hr < 0)
+               new_hr = 0;
+
+       rcu_read_lock();
+       peer = rcu_dereference(priv->peer);
+       if (unlikely(!peer))
+               goto out;
+
+       peer_priv = netdev_priv(peer);
+       priv->requested_headroom = new_hr;
+       new_hr = max(priv->requested_headroom, peer_priv->requested_headroom);
+       dev->needed_headroom = new_hr;
+       peer->needed_headroom = new_hr;
+
+out:
+       rcu_read_unlock();
+}
+
 static const struct net_device_ops veth_netdev_ops = {
        .ndo_init            = veth_dev_init,
        .ndo_open            = veth_open,
@@ -285,6 +309,7 @@ static const struct net_device_ops veth_netdev_ops = {
 #endif
        .ndo_get_iflink         = veth_get_iflink,
        .ndo_features_check     = passthru_features_check,
+       .ndo_set_rx_headroom    = veth_set_rx_headroom,
 };
 
 #define VETH_FEATURES (NETIF_F_SG | NETIF_F_FRAGLIST | NETIF_F_ALL_TSO |    \
@@ -301,6 +326,7 @@ static void veth_setup(struct net_device *dev)
        dev->priv_flags &= ~IFF_TX_SKB_SHARING;
        dev->priv_flags |= IFF_LIVE_ADDR_CHANGE;
        dev->priv_flags |= IFF_NO_QUEUE;
+       dev->priv_flags |= IFF_PHONY_HEADROOM;
 
        dev->netdev_ops = &veth_netdev_ops;
        dev->ethtool_ops = &veth_ethtool_ops;