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net: No dst refcounting in ip_queue_xmit()

Browse source 
TCP outgoing packets can avoid two atomic ops, and dirtying
of previously higly contended cache line using new refdst
infrastructure.

Note 1: loopback device excluded because of !IFF_XMIT_DST_RELEASE
Note 2: UDP packets dsts are built before ip_queue_xmit().

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet 2010-05-10 11:31:49 +00:00 committed by David S. Miller
parent 4a94445c9a
commit ab6e3feba1
1 changed files with 7 additions and 2 deletions
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9
net/ipv4/ip_output.c
View file

@ -318,10 +318,12 @@ int ip_queue_xmit(struct sk_buff *skb)
struct ip_options *opt = inet->opt;
struct rtable *rt;
struct iphdr *iph;
int res;
/* Skip all of this if the packet is already routed,
* f.e. by something like SCTP.
*/
rcu_read_lock();
rt = skb_rtable(skb);
if (rt != NULL)
goto packet_routed;
@ -359,7 +361,7 @@ int ip_queue_xmit(struct sk_buff *skb)
}
sk_setup_caps(sk, &rt->u.dst);
}
skb_dst_set(skb, dst_clone(&rt->u.dst));
skb_dst_set_noref(skb, &rt->u.dst);
packet_routed:
if (opt && opt->is_strictroute && rt->rt_dst != rt->rt_gateway)
@ -391,9 +393,12 @@ int ip_queue_xmit(struct sk_buff *skb)
skb->priority = sk->sk_priority;
skb->mark = sk->sk_mark;
return ip_local_out(skb);
res = ip_local_out(skb);
rcu_read_unlock();
return res;
no_route:
rcu_read_unlock();
IP_INC_STATS(sock_net(sk), IPSTATS_MIB_OUTNOROUTES);
kfree_skb(skb);
return -EHOSTUNREACH;