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>
diff --git a/include/net/udp.h b/include/net/udp.h
index 1e20509..df2bfe5 100644
--- a/include/net/udp.h
+++ b/include/net/udp.h
@@ -50,8 +50,15 @@
};
#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 @@
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 @@
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 seq_net_private p;
sa_family_t family;
int bucket;
- struct hlist_head *hashtable;
+ struct udp_table *udp_table;
};
#ifdef CONFIG_PROC_FS