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authorEric Dumazet <dada1@cosmosbay.com>2009-05-19 01:19:19 -0400
committerDavid S. Miller <davem@davemloft.net>2009-05-19 01:19:19 -0400
commit93f154b594fe47e4a7e5358b309add449a046cd3 (patch)
tree479d9f2db25922a2312547c97e73d5a11b68bb1c /drivers/net/macvlan.c
parent496a60cdcd5d0d884dddf6c3b4ea912923a70f13 (diff)
net: release dst entry in dev_hard_start_xmit()
One point of contention in high network loads is the dst_release() performed when a transmited skb is freed. This is because NIC tx completion calls dev_kree_skb() long after original call to dev_queue_xmit(skb). CPU cache is cold and the atomic op in dst_release() stalls. On SMP, this is quite visible if one CPU is 100% handling softirqs for a network device, since dst_clone() is done by other cpus, involving cache line ping pongs. It seems right place to release dst is in dev_hard_start_xmit(), for most devices but ones that are virtual, and some exceptions. David Miller suggested to define a new device flag, set in alloc_netdev_mq() (so that most devices set it at init time), and carefuly unset in devices which dont want a NULL skb->dst in their ndo_start_xmit(). List of devices that must clear this flag is : - loopback device, because it calls netif_rx() and quoting Patrick : "ip_route_input() doesn't accept loopback addresses, so loopback packets already need to have a dst_entry attached." - appletalk/ipddp.c : needs skb->dst in its xmit function - And all devices that call again dev_queue_xmit() from their xmit function (as some classifiers need skb->dst) : bonding, vlan, macvlan, eql, ifb, hdlc_fr Signed-off-by: Eric Dumazet <dada1@cosmosbay.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'drivers/net/macvlan.c')
-rw-r--r--drivers/net/macvlan.c1
1 files changed, 1 insertions, 0 deletions
diff --git a/drivers/net/macvlan.c b/drivers/net/macvlan.c
index 329cd50d0e29..d5334b41e4b4 100644
--- a/drivers/net/macvlan.c
+++ b/drivers/net/macvlan.c
@@ -414,6 +414,7 @@ static void macvlan_setup(struct net_device *dev)
414{ 414{
415 ether_setup(dev); 415 ether_setup(dev);
416 416
417 dev->priv_flags &= ~IFF_XMIT_DST_RELEASE;
417 dev->netdev_ops = &macvlan_netdev_ops; 418 dev->netdev_ops = &macvlan_netdev_ops;
418 dev->destructor = free_netdev; 419 dev->destructor = free_netdev;
419 dev->header_ops = &macvlan_hard_header_ops, 420 dev->header_ops = &macvlan_hard_header_ops,