diff options
| author | Eric Dumazet <dada1@cosmosbay.com> | 2009-05-18 22:19:19 -0700 |
|---|---|---|
| committer | David S. Miller <davem@davemloft.net> | 2009-05-18 22:19:19 -0700 |
| commit | 93f154b594fe47e4a7e5358b309add449a046cd3 (patch) | |
| tree | 479d9f2db25922a2312547c97e73d5a11b68bb1c /drivers/net/appletalk | |
| parent | 496a60cdcd5d0d884dddf6c3b4ea912923a70f13 (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/appletalk')
| -rw-r--r-- | drivers/net/appletalk/ipddp.c | 1 |
1 files changed, 1 insertions, 0 deletions
diff --git a/drivers/net/appletalk/ipddp.c b/drivers/net/appletalk/ipddp.c index da64ba88d7f..f939e92fcf8 100644 --- a/drivers/net/appletalk/ipddp.c +++ b/drivers/net/appletalk/ipddp.c @@ -71,6 +71,7 @@ static struct net_device * __init ipddp_init(void) if (!dev) return ERR_PTR(-ENOMEM); + dev->priv_flags &= ~IFF_XMIT_DST_RELEASE; strcpy(dev->name, "ipddp%d"); if (version_printed++ == 0) |