udp: introduce struct udp_table and multiple spinlocks

UDP sockets are hashed in a 128 slots hash table.

This hash table is protected by *one* rwlock.

This rwlock is readlocked each time an incoming UDP message is handled.

This rwlock is writelocked each time a socket must be inserted in
hash table (bind time), or deleted from this table (close time)

This is not scalable on SMP machines :

1) Even in read mode, lock() and unlock() are atomic operations and
 must dirty a contended cache line, shared by all cpus.

2) A writer might be starved if many readers are 'in flight'. This can
 happen on a machine with some NIC receiving many UDP messages. User
 process can be delayed a long time at socket creation/dismantle time.

This patch prepares RCU migration, by introducing 'struct udp_table
and struct udp_hslot', and using one spinlock per chain, to reduce
contention on central rwlock.

Introducing one spinlock per chain reduces latencies, for port
randomization on heavily loaded UDP servers. This also speedup
bindings to specific ports.

udp_lib_unhash() was uninlined, becoming to big.

Some cleanups were done to ease review of following patch
(RCUification of UDP Unicast lookups)

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

1 files changed, 12 insertions, 13 deletions

diff --git a/include/net/udp.h b/include/net/udp.h
index 1e205095ea68..df2bfe545374 100644
--- a/include/net/udp.h
+++ b/include/net/udp.h
@@ -50,8 +50,15 @@ struct udp_skb_cb {
 };
 #define UDP_SKB_CB(__skb)       ((struct udp_skb_cb *)((__skb)->cb))
 
-extern struct hlist_head udp_hash[UDP_HTABLE_SIZE];
-extern rwlock_t udp_hash_lock;
+struct udp_hslot {
+        struct hlist_head       head;
+        spinlock_t              lock;
+} __attribute__((aligned(2 * sizeof(long))));
+struct udp_table {
+        struct udp_hslot        hash[UDP_HTABLE_SIZE];
+};
+extern struct udp_table udp_table;
+extern void udp_table_init(struct udp_table *);
 
 
 /* Note: this must match 'valbool' in sock_setsockopt */
@@ -110,15 +117,7 @@ static inline void udp_lib_hash(struct sock *sk)
         BUG();
 }
 
-static inline void udp_lib_unhash(struct sock *sk)
-{
-        write_lock_bh(&udp_hash_lock);
-        if (sk_del_node_init(sk)) {
-                inet_sk(sk)->num = 0;
-                sock_prot_inuse_add(sock_net(sk), sk->sk_prot, -1);
-        }
-        write_unlock_bh(&udp_hash_lock);
-}
+extern void udp_lib_unhash(struct sock *sk);
 
 static inline void udp_lib_close(struct sock *sk, long timeout)
 {
@@ -187,7 +186,7 @@ extern struct sock *udp4_lib_lookup(struct net *net, __be32 saddr, __be16 sport,
 struct udp_seq_afinfo {
         char                    *name;
         sa_family_t             family;
-        struct hlist_head       *hashtable;
+        struct udp_table        *udp_table;
         struct file_operations  seq_fops;
         struct seq_operations   seq_ops;
 };
@@ -196,7 +195,7 @@ struct udp_iter_state {
         struct seq_net_private  p;
         sa_family_t             family;
         int                     bucket;
-        struct hlist_head       *hashtable;
+        struct udp_table        *udp_table;
 };
 
 #ifdef CONFIG_PROC_FS