netdev - [PATCH net-next] openvswitch: do not propagate headroom updates to internal port

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Date:   Thu, 30 Nov 2017 15:35:33 +0100
From:   Paolo Abeni <pabeni@...hat.com>
To:     netdev@...r.kernel.org
Cc:     Pravin Shelar <pshelar@...ira.com>,
        "David S. Miller" <davem@...emloft.net>
Subject: [PATCH net-next] 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@...hat.com>
---
 net/openvswitch/vport-internal_dev.c | 9 +--------
 1 file changed, 1 insertion(+), 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);
-- 
2.13.6