netdev - [PATCH net-next v3 5/5] veth: implement ndo_set_rx

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Message-Id: <cd429db8d0dc5c981bdce7d282b0f351417a6e60.1456412101.git.pabeni@redhat.com>
Date:	Fri, 26 Feb 2016 10:45:41 +0100
From:	Paolo Abeni <pabeni@...hat.com>
To:	netdev@...r.kernel.org
Cc:	"David S. Miller" <davem@...emloft.net>,
	Stephen Hemminger <stephen@...workplumber.org>,
	Pravin Shelar <pshelar@...ira.com>,
	Jesse Gross <jesse@...nel.org>,
	Flavio Leitner <fbl@...close.org>,
	Hannes Frederic Sowa <hannes@...essinduktion.org>,
	Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
Subject: [PATCH net-next v3 5/5] 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@...hat.com>
---
 drivers/net/veth.c | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/drivers/net/veth.c b/drivers/net/veth.c
index ba21d07..4f30a6a 100644
--- 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;
-- 
1.8.3.1