ipv6: udp: optimize unicast RX path

We first locate the (local port) hash chain head
If few sockets are in this chain, we proceed with previous lookup algo.

If too many sockets are listed, we take a look at the secondary
(port, address) hash chain.

We choose the shortest chain and proceed with a RCU lookup on the elected chain.

But, if we chose (port, address) chain, and fail to find a socket on given address,
 we must try another lookup on (port, in6addr_any) chain to find sockets not bound
to a particular IP.

-> No extra cost for typical setups, where the first lookup will probabbly
be performed.

RCU lookups everywhere, we dont acquire spinlock.
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/udp.c

@@ -146,6 +146,88 @@ static inline int compute_score(struct sock *sk, struct net *net,
 	return score;
 }
 
+#define SCORE2_MAX (1 + 1 + 1)
+static inline int compute_score2(struct sock *sk, struct net *net,
+				const struct in6_addr *saddr, __be16 sport,
+				const struct in6_addr *daddr, unsigned short hnum,
+				int dif)
+{
+	int score = -1;
+
+	if (net_eq(sock_net(sk), net) && udp_sk(sk)->udp_port_hash == hnum &&
+			sk->sk_family == PF_INET6) {
+		struct ipv6_pinfo *np = inet6_sk(sk);
+		struct inet_sock *inet = inet_sk(sk);
+
+		if (!ipv6_addr_equal(&np->rcv_saddr, daddr))
+			return -1;
+		score = 0;
+		if (inet->inet_dport) {
+			if (inet->inet_dport != sport)
+				return -1;
+			score++;
+		}
+		if (!ipv6_addr_any(&np->daddr)) {
+			if (!ipv6_addr_equal(&np->daddr, saddr))
+				return -1;
+			score++;
+		}
+		if (sk->sk_bound_dev_if) {
+			if (sk->sk_bound_dev_if != dif)
+				return -1;
+			score++;
+		}
+	}
+	return score;
+}
+
+#define udp_portaddr_for_each_entry_rcu(__sk, node, list) \
+	hlist_nulls_for_each_entry_rcu(__sk, node, list, __sk_common.skc_portaddr_node)
+
+/* called with read_rcu_lock() */
+static struct sock *udp6_lib_lookup2(struct net *net,
+		const struct in6_addr *saddr, __be16 sport,
+		const struct in6_addr *daddr, unsigned int hnum, int dif,
+		struct udp_hslot *hslot2, unsigned int slot2)
+{
+	struct sock *sk, *result;
+	struct hlist_nulls_node *node;
+	int score, badness;
+
+begin:
+	result = NULL;
+	badness = -1;
+	udp_portaddr_for_each_entry_rcu(sk, node, &hslot2->head) {
+		score = compute_score2(sk, net, saddr, sport,
+				      daddr, hnum, dif);
+		if (score > badness) {
+			result = sk;
+			badness = score;
+			if (score == SCORE2_MAX)
+				goto exact_match;
+		}
+	}
+	/*
+	 * if the nulls value we got at the end of this lookup is
+	 * not the expected one, we must restart lookup.
+	 * We probably met an item that was moved to another chain.
+	 */
+	if (get_nulls_value(node) != slot2)
+		goto begin;
+
+	if (result) {
+exact_match:
+		if (unlikely(!atomic_inc_not_zero(&result->sk_refcnt)))
+			result = NULL;
+		else if (unlikely(compute_score2(result, net, saddr, sport,
+				  daddr, hnum, dif) < badness)) {
+			sock_put(result);
+			goto begin;
+		}
+	}
+	return result;
+}
+
 static struct sock *__udp6_lib_lookup(struct net *net,
 				      struct in6_addr *saddr, __be16 sport,
 				      struct in6_addr *daddr, __be16 dport,
@@ -154,11 +236,35 @@ static struct sock *__udp6_lib_lookup(struct net *net,
 	struct sock *sk, *result;
 	struct hlist_nulls_node *node;
 	unsigned short hnum = ntohs(dport);
-	unsigned int hash = udp_hashfn(net, hnum, udptable->mask);
-	struct udp_hslot *hslot = &udptable->hash[hash];
+	unsigned int hash2, slot2, slot = udp_hashfn(net, hnum, udptable->mask);
+	struct udp_hslot *hslot2, *hslot = &udptable->hash[slot];
 	int score, badness;
 
 	rcu_read_lock();
+	if (hslot->count > 10) {
+		hash2 = udp6_portaddr_hash(net, daddr, hnum);
+		slot2 = hash2 & udptable->mask;
+		hslot2 = &udptable->hash2[slot2];
+		if (hslot->count < hslot2->count)
+			goto begin;
+
+		result = udp6_lib_lookup2(net, saddr, sport,
+					  daddr, hnum, dif,
+					  hslot2, slot2);
+		if (!result) {
+			hash2 = udp6_portaddr_hash(net, &in6addr_any, hnum);
+			slot2 = hash2 & udptable->mask;
+			hslot2 = &udptable->hash2[slot2];
+			if (hslot->count < hslot2->count)
+				goto begin;
+
+			result = udp6_lib_lookup2(net, &in6addr_any, sport,
+						  daddr, hnum, dif,
+						  hslot2, slot2);
+		}
+		rcu_read_unlock();
+		return result;
+	}
 begin:
 	result = NULL;
 	badness = -1;
@@ -174,7 +280,7 @@ begin:
 	 * not the expected one, we must restart lookup.
 	 * We probably met an item that was moved to another chain.
 	 */
-	if (get_nulls_value(node) != hash)
+	if (get_nulls_value(node) != slot)
 		goto begin;
 
 	if (result) {