From a21bba945430f3f5e00c349665f88cdacdb32a8d Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Mon, 24 Nov 2008 16:07:50 -0800 Subject: net: avoid a pair of dst_hold()/dst_release() in ip_push_pending_frames() We can reduce pressure on dst entry refcount that slowdown UDP transmit path on SMP machines. This pressure is visible on RTP servers when delivering content to mediagateways, especially big ones, handling thousand of streams. Several cpus send UDP frames to the same destination, hence use the same dst entry. This patch makes ip_push_pending_frames() steal the refcount its callers had to take when filling inet->cork.dst. This doesnt avoid all refcounting, but still gives speedups on SMP, on UDP/RAW transmit path. Signed-off-by: Eric Dumazet Signed-off-by: David S. Miller --- net/ipv4/ip_output.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) (limited to 'net') diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c index 5516825..8ebe86dd 100644 --- a/net/ipv4/ip_output.c +++ b/net/ipv4/ip_output.c @@ -1284,7 +1284,12 @@ int ip_push_pending_frames(struct sock *sk) skb->priority = sk->sk_priority; skb->mark = sk->sk_mark; - skb->dst = dst_clone(&rt->u.dst); + /* + * Steal rt from cork.dst to avoid a pair of atomic_inc/atomic_dec + * on dst refcount + */ + inet->cork.dst = NULL; + skb->dst = &rt->u.dst; if (iph->protocol == IPPROTO_ICMP) icmp_out_count(net, ((struct icmphdr *) -- cgit v1.1