net: do not read sk_drops if application does not care
authorEric Dumazet <edumazet@google.com>
Wed, 7 Dec 2016 18:05:36 +0000 (10:05 -0800)
committerDavid S. Miller <davem@davemloft.net>
Thu, 8 Dec 2016 18:30:22 +0000 (13:30 -0500)
sk_drops can be an often written field, do not read it unless
application showed interest.

Note that sk_drops can be read via inet_diag, so applications
can avoid getting this info from every received packet.

In the future, 'reading' sk_drops might require folding per node or per
cpu fields, and thus become even more expensive than today.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
include/net/sock.h

index 2729e77..e17aa3d 100644 (file)
@@ -2163,7 +2163,8 @@ struct sock_skb_cb {
 static inline void
 sock_skb_set_dropcount(const struct sock *sk, struct sk_buff *skb)
 {
-       SOCK_SKB_CB(skb)->dropcount = atomic_read(&sk->sk_drops);
+       SOCK_SKB_CB(skb)->dropcount = sock_flag(sk, SOCK_RXQ_OVFL) ?
+                                               atomic_read(&sk->sk_drops) : 0;
 }
 
 static inline void sk_drops_add(struct sock *sk, const struct sk_buff *skb)