net: do not read sk_drops if application does not care

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>
This commit is contained in:
Eric Dumazet 2016-12-07 10:05:36 -08:00 коммит произвёл David S. Miller
Родитель c8c8b12709
Коммит 3665f3817c
1 изменённых файлов: 2 добавлений и 1 удалений

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@ -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)