openvswitch: do not propagate headroom updates to internal port

After commit 3a927bc7cf9d ("ovs: propagate per dp max headroom to
all vports") the need_headroom for the internal vport is updated
accordingly to the max needed headroom in its datapath.

That avoids the pskb_expand_head() costs when sending/forwarding
packets towards tunnel devices, at least for some scenarios.

We still require such copy when using the ovs-preferred configuration
for vxlan tunnels:

    br_int
  /       \
tap      vxlan
           (remote_ip:X)

br_phy
     \
    NIC

where the route towards the IP 'X' is via 'br_phy'.

When forwarding traffic from the tap towards the vxlan device, we
will call pskb_expand_head() in vxlan_build_skb() because
br-phy->needed_headroom is equal to tun->needed_headroom.

With this change we avoid updating the internal vport needed_headroom,
so that in the above scenario no head copy is needed, giving 5%
performance improvement in UDP throughput test.

As a trade-off, packets sent from the internal port towards a tunnel
device will now experience the head copy overhead. The rationale is
that the latter use-case is less relevant performance-wise.

Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Acked-by: Pravin B Shelar <pshelar@ovn.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 1 insertions, 8 deletions

diff --git a/net/openvswitch/vport-internal_dev.c b/net/openvswitch/vport-internal_dev.c
index 04a3128adcf0..3e7747549f90 100644
--- a/net/openvswitch/vport-internal_dev.c
+++ b/net/openvswitch/vport-internal_dev.c
@@ -126,18 +126,12 @@ internal_get_stats(struct net_device *dev, struct rtnl_link_stats64 *stats)
         }
 }
 
-static void internal_set_rx_headroom(struct net_device *dev, int new_hr)
-{
-        dev->needed_headroom = new_hr < 0 ? 0 : new_hr;
-}
-
 static const struct net_device_ops internal_dev_netdev_ops = {
         .ndo_open = internal_dev_open,
         .ndo_stop = internal_dev_stop,
         .ndo_start_xmit = internal_dev_xmit,
         .ndo_set_mac_address = eth_mac_addr,
         .ndo_get_stats64 = internal_get_stats,
-        .ndo_set_rx_headroom = internal_set_rx_headroom,
 };
 
 static struct rtnl_link_ops internal_dev_link_ops __read_mostly = {
@@ -154,7 +148,7 @@ static void do_setup(struct net_device *netdev)
 
         netdev->priv_flags &= ~IFF_TX_SKB_SHARING;
         netdev->priv_flags |= IFF_LIVE_ADDR_CHANGE | IFF_OPENVSWITCH |
-                              IFF_PHONY_HEADROOM | IFF_NO_QUEUE;
+                              IFF_NO_QUEUE;
         netdev->needs_free_netdev = true;
         netdev->priv_destructor = internal_dev_destructor;
         netdev->ethtool_ops = &internal_dev_ethtool_ops;
@@ -195,7 +189,6 @@ static struct vport *internal_dev_create(const struct vport_parms *parms)
                 err = -ENOMEM;
                 goto error_free_netdev;
         }
-        vport->dev->needed_headroom = vport->dp->max_headroom;
 
         dev_net_set(vport->dev, ovs_dp_get_net(vport->dp));
         internal_dev = internal_dev_priv(vport->dev);