net: release skb->dst in sock_queue_rcv_skb()

When queuing a skb to sk->sk_receive_queue, we can release its dst,
not anymore needed.  Since current cpu did the dst_hold(), refcount is
probably still hot int this cpu caches.

This avoids readers to access the original dst to decrement its
refcount, possibly a long time after packet reception. This should
speedup UDP and RAW receive path.

Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/core/sock.c b/net/core/sock.c
index 7a081b647bf9d07370f69ba97e951fdc7599f65f..b28764558a7d4a1d4e9428c9be1812f52fe26568 100644 (file)
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -289,7 +289,11 @@ int sock_queue_rcv_skb(struct sock *sk, struct sk_buff *skb)
 
        skb->dev = NULL;
        skb_set_owner_r(skb, sk);
-
+       /*
+        * release dst right now while its hot
+        */
+       dst_release(skb->dst);
+       skb->dst = NULL;
        /* Cache the SKB length before we tack it onto the receive
         * queue.  Once it is added it no longer belongs to us and
         * may be freed by other threads of control pulling packets