[PATCH] NET : UDP can use sk_hash to speedup lookups

[Eric Dumazet]

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 <[EMAIL PROTECTED]>

--- linux-2.6.20/net/ipv4/udp.c 2007-02-09 19:17:28.000000000 +0100
+++ linux-2.6.20-ed/net/ipv4/udp.c      2007-02-09 19:21:07.000000000 +0100
@@ -120,7 +120,7 @@ static inline int __udp_lib_lport_inuse(
        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 @@ gotit:
                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 @@ gotit:
                                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(__
        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_
        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)    ||
--- linux-2.6.20/net/ipv6/udp.c 2007-02-09 19:17:28.000000000 +0100
+++ linux-2.6.20-ed/net/ipv6/udp.c      2007-02-09 19:17:28.000000000 +0100
@@ -71,7 +71,7 @@ static struct sock *__udp6_lib_lookup(st
        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(st
        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)