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authorEric Dumazet <dada1@cosmosbay.com>2009-05-19 09:19:19 +0400
committerDavid S. Miller <davem@davemloft.net>2009-05-19 09:19:19 +0400
commit93f154b594fe47e4a7e5358b309add449a046cd3 (patch)
tree479d9f2db25922a2312547c97e73d5a11b68bb1c /drivers/net/loopback.c
parent496a60cdcd5d0d884dddf6c3b4ea912923a70f13 (diff)
downloadlinux-93f154b594fe47e4a7e5358b309add449a046cd3.tar.xz
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/loopback.c')
-rw-r--r--drivers/net/loopback.c1
1 files changed, 1 insertions, 0 deletions
diff --git a/drivers/net/loopback.c b/drivers/net/loopback.c
index 6f71157bea8e..da472c687481 100644
--- a/drivers/net/loopback.c
+++ b/drivers/net/loopback.c
@@ -170,6 +170,7 @@ static void loopback_setup(struct net_device *dev)
dev->tx_queue_len = 0;
dev->type = ARPHRD_LOOPBACK; /* 0x0001*/
dev->flags = IFF_LOOPBACK;
+ dev->priv_flags &= ~IFF_XMIT_DST_RELEASE;
dev->features = NETIF_F_SG | NETIF_F_FRAGLIST
| NETIF_F_TSO
| NETIF_F_NO_CSUM