[UDP]: UDP can use sk_hash to speedup lookups

In a prior patch, I introduced a sk_hash field (__sk_common.skc_hash)  to let
tcp lookups use one cache line per unmatched entry instead of two.

We can also use sk_hash to speedup UDP part as well. We store in sk_hash the
hnum value, and use sk->sk_hash (same cache line than 'next' pointer),
instead of inet->num (different cache line)

Note : We still have a false sharing problem for SMP machines, because
sock_hold(sock) dirties the cache line containing the 'next' pointer. Not
counting the udp_hash_lock rwlock. (did someone mentioned RCU ? :) )

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

net/ipv4/udp.c

@@ -120,7 +120,7 @@ static inline int __udp_lib_lport_inuse(__u16 num, struct hlist_head udptable[])
 	struct hlist_node *node;
 
 	sk_for_each(sk, node, &udptable[num & (UDP_HTABLE_SIZE - 1)])
-		if (inet_sk(sk)->num == num)
+		if (sk->sk_hash == num)
 			return 1;
 	return 0;
 }
@@ -191,7 +191,7 @@ int __udp_lib_get_port(struct sock *sk, unsigned short snum,
 		head = &udptable[snum & (UDP_HTABLE_SIZE - 1)];
 
 		sk_for_each(sk2, node, head)
-			if (inet_sk(sk2)->num == snum                        &&
+			if (sk2->sk_hash == snum                             &&
 			    sk2 != sk                                        &&
 			    (!sk2->sk_reuse        || !sk->sk_reuse)         &&
 			    (!sk2->sk_bound_dev_if || !sk->sk_bound_dev_if
@@ -200,6 +200,7 @@ int __udp_lib_get_port(struct sock *sk, unsigned short snum,
 				goto fail;
 	}
 	inet_sk(sk)->num = snum;
+	sk->sk_hash = snum;
 	if (sk_unhashed(sk)) {
 		head = &udptable[snum & (UDP_HTABLE_SIZE - 1)];
 		sk_add_node(sk, head);
@@ -247,7 +248,7 @@ static struct sock *__udp4_lib_lookup(__be32 saddr, __be16 sport,
 	sk_for_each(sk, node, &udptable[hnum & (UDP_HTABLE_SIZE - 1)]) {
 		struct inet_sock *inet = inet_sk(sk);
 
-		if (inet->num == hnum && !ipv6_only_sock(sk)) {
+		if (sk->sk_hash == hnum && !ipv6_only_sock(sk)) {
 			int score = (sk->sk_family == PF_INET ? 1 : 0);
 			if (inet->rcv_saddr) {
 				if (inet->rcv_saddr != daddr)
@@ -296,7 +297,7 @@ static inline struct sock *udp_v4_mcast_next(struct sock *sk,
 	sk_for_each_from(s, node) {
 		struct inet_sock *inet = inet_sk(s);
 
-		if (inet->num != hnum					||
+		if (s->sk_hash != hnum					||
 		    (inet->daddr && inet->daddr != rmt_addr)		||
 		    (inet->dport != rmt_port && inet->dport)		||
 		    (inet->rcv_saddr && inet->rcv_saddr != loc_addr)	||

net/ipv6/udp.c

@@ -71,7 +71,7 @@ static struct sock *__udp6_lib_lookup(struct in6_addr *saddr, __be16 sport,
 	sk_for_each(sk, node, &udptable[hnum & (UDP_HTABLE_SIZE - 1)]) {
 		struct inet_sock *inet = inet_sk(sk);
 
-		if (inet->num == hnum && sk->sk_family == PF_INET6) {
+		if (sk->sk_hash == hnum && sk->sk_family == PF_INET6) {
 			struct ipv6_pinfo *np = inet6_sk(sk);
 			int score = 0;
 			if (inet->dport) {
@@ -309,7 +309,7 @@ static struct sock *udp_v6_mcast_next(struct sock *sk,
 	sk_for_each_from(s, node) {
 		struct inet_sock *inet = inet_sk(s);
 
-		if (inet->num == num && s->sk_family == PF_INET6) {
+		if (s->sk_hash == num && s->sk_family == PF_INET6) {
 			struct ipv6_pinfo *np = inet6_sk(s);
 			if (inet->dport) {
 				if (inet->dport != rmt_port)