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>

include/net/sock.h

@@ -599,7 +599,7 @@ struct proto {
 
 	union {
 		struct inet_hashinfo	*hashinfo;
-		struct hlist_head	*udp_hash;
+		struct udp_table	*udp_table;
 		struct raw_hashinfo	*raw_hash;
 	} h;
 

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

include/net/udplite.h

@@ -11,7 +11,7 @@
 #define UDPLITE_RECV_CSCOV   11 /* receiver partial coverage (threshold ) */
 
 extern struct proto 		udplite_prot;
-extern struct hlist_head 	udplite_hash[UDP_HTABLE_SIZE];
+extern struct udp_table		udplite_table;
 
 /*
  *	Checksum computation is all in software, hence simpler getfrag.

net/ipv4/udp_impl.h

@@ -5,8 +5,8 @@
 #include <net/protocol.h>
 #include <net/inet_common.h>
 
-extern int  	__udp4_lib_rcv(struct sk_buff *, struct hlist_head [], int );
-extern void 	__udp4_lib_err(struct sk_buff *, u32, struct hlist_head []);
+extern int  	__udp4_lib_rcv(struct sk_buff *, struct udp_table *, int );
+extern void 	__udp4_lib_err(struct sk_buff *, u32, struct udp_table *);
 
 extern int	udp_v4_get_port(struct sock *sk, unsigned short snum);
 

net/ipv4/udplite.c

@@ -12,16 +12,17 @@
  */
 #include "udp_impl.h"
 
-struct hlist_head 	udplite_hash[UDP_HTABLE_SIZE];
+struct udp_table 	udplite_table;
+EXPORT_SYMBOL(udplite_table);
 
 static int udplite_rcv(struct sk_buff *skb)
 {
-	return __udp4_lib_rcv(skb, udplite_hash, IPPROTO_UDPLITE);
+	return __udp4_lib_rcv(skb, &udplite_table, IPPROTO_UDPLITE);
 }
 
 static void udplite_err(struct sk_buff *skb, u32 info)
 {
-	__udp4_lib_err(skb, info, udplite_hash);
+	__udp4_lib_err(skb, info, &udplite_table);
 }
 
 static	struct net_protocol udplite_protocol = {
@@ -50,7 +51,7 @@ struct proto 	udplite_prot = {
 	.unhash		   = udp_lib_unhash,
 	.get_port	   = udp_v4_get_port,
 	.obj_size	   = sizeof(struct udp_sock),
-	.h.udp_hash	   = udplite_hash,
+	.h.udp_table	   = &udplite_table,
 #ifdef CONFIG_COMPAT
 	.compat_setsockopt = compat_udp_setsockopt,
 	.compat_getsockopt = compat_udp_getsockopt,
@@ -71,7 +72,7 @@ static struct inet_protosw udplite4_protosw = {
 static struct udp_seq_afinfo udplite4_seq_afinfo = {
 	.name		= "udplite",
 	.family		= AF_INET,
-	.hashtable	= udplite_hash,
+	.udp_table 	= &udplite_table,
 	.seq_fops	= {
 		.owner	=	THIS_MODULE,
 	},
@@ -108,6 +109,7 @@ static inline int udplite4_proc_init(void)
 
 void __init udplite4_register(void)
 {
+	udp_table_init(&udplite_table);
 	if (proto_register(&udplite_prot, 1))
 		goto out_register_err;
 
@@ -126,5 +128,4 @@ void __init udplite4_register(void)
 	printk(KERN_CRIT "%s: Cannot add UDP-Lite protocol.\n", __func__);
 }
 
-EXPORT_SYMBOL(udplite_hash);
 EXPORT_SYMBOL(udplite_prot);

net/ipv6/udp.c

@@ -54,62 +54,73 @@ int udp_v6_get_port(struct sock *sk, unsigned short snum)
 	return udp_lib_get_port(sk, snum, ipv6_rcv_saddr_equal);
 }
 
+static inline int compute_score(struct sock *sk, struct net *net,
+				unsigned short hnum,
+				struct in6_addr *saddr, __be16 sport,
+				struct in6_addr *daddr, __be16 dport,
+				int dif)
+{
+	int score = -1;
+
+	if (net_eq(sock_net(sk), net) && sk->sk_hash == hnum &&
+			sk->sk_family == PF_INET6) {
+		struct ipv6_pinfo *np = inet6_sk(sk);
+		struct inet_sock *inet = inet_sk(sk);
+
+		score = 0;
+		if (inet->dport) {
+			if (inet->dport != sport)
+				return -1;
+			score++;
+		}
+		if (!ipv6_addr_any(&np->rcv_saddr)) {
+			if (!ipv6_addr_equal(&np->rcv_saddr, daddr))
+				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;
+}
+
 static struct sock *__udp6_lib_lookup(struct net *net,
 				      struct in6_addr *saddr, __be16 sport,
 				      struct in6_addr *daddr, __be16 dport,
-				      int dif, struct hlist_head udptable[])
+				      int dif, struct udp_table *udptable)
 {
 	struct sock *sk, *result = NULL;
 	struct hlist_node *node;
 	unsigned short hnum = ntohs(dport);
-	int badness = -1;
-
-	read_lock(&udp_hash_lock);
-	sk_for_each(sk, node, &udptable[udp_hashfn(net, hnum)]) {
-		struct inet_sock *inet = inet_sk(sk);
-
-		if (net_eq(sock_net(sk), net) && sk->sk_hash == hnum &&
-				sk->sk_family == PF_INET6) {
-			struct ipv6_pinfo *np = inet6_sk(sk);
-			int score = 0;
-			if (inet->dport) {
-				if (inet->dport != sport)
-					continue;
-				score++;
-			}
-			if (!ipv6_addr_any(&np->rcv_saddr)) {
-				if (!ipv6_addr_equal(&np->rcv_saddr, daddr))
-					continue;
-				score++;
-			}
-			if (!ipv6_addr_any(&np->daddr)) {
-				if (!ipv6_addr_equal(&np->daddr, saddr))
-					continue;
-				score++;
-			}
-			if (sk->sk_bound_dev_if) {
-				if (sk->sk_bound_dev_if != dif)
-					continue;
-				score++;
-			}
-			if (score == 4) {
-				result = sk;
-				break;
-			} else if (score > badness) {
-				result = sk;
-				badness = score;
-			}
+	unsigned int hash = udp_hashfn(net, hnum);
+	struct udp_hslot *hslot = &udptable->hash[hash];
+	int score, badness = -1;
+
+	spin_lock(&hslot->lock);
+	sk_for_each(sk, node, &hslot->head) {
+		score = compute_score(sk, net, hnum, saddr, sport, daddr, dport, dif);
+		if (score > badness) {
+			result = sk;
+			badness = score;
 		}
 	}
 	if (result)
 		sock_hold(result);
-	read_unlock(&udp_hash_lock);
+	spin_unlock(&hslot->lock);
 	return result;
 }
 
 static struct sock *__udp6_lib_lookup_skb(struct sk_buff *skb,
 					  __be16 sport, __be16 dport,
-					  struct hlist_head udptable[])
+					  struct udp_table *udptable)
 {
 	struct sock *sk;
 	struct ipv6hdr *iph = ipv6_hdr(skb);
@@ -239,7 +250,7 @@ int udpv6_recvmsg(struct kiocb *iocb, struct sock *sk,
 
 void __udp6_lib_err(struct sk_buff *skb, struct inet6_skb_parm *opt,
 		    int type, int code, int offset, __be32 info,
-		    struct hlist_head udptable[]                    )
+		    struct udp_table *udptable)
 {
 	struct ipv6_pinfo *np;
 	struct ipv6hdr *hdr = (struct ipv6hdr*)skb->data;
@@ -275,7 +286,7 @@ static __inline__ void udpv6_err(struct sk_buff *skb,
 				 struct inet6_skb_parm *opt, int type,
 				 int code, int offset, __be32 info     )
 {
-	__udp6_lib_err(skb, opt, type, code, offset, info, udp_hash);
+	__udp6_lib_err(skb, opt, type, code, offset, info, &udp_table);
 }
 
 int udpv6_queue_rcv_skb(struct sock * sk, struct sk_buff *skb)
@@ -374,14 +385,15 @@ static struct sock *udp_v6_mcast_next(struct sock *sk,
  */
 static int __udp6_lib_mcast_deliver(struct net *net, struct sk_buff *skb,
 		struct in6_addr *saddr, struct in6_addr *daddr,
-		struct hlist_head udptable[])
+		struct udp_table *udptable)
 {
 	struct sock *sk, *sk2;
 	const struct udphdr *uh = udp_hdr(skb);
+	struct udp_hslot *hslot = &udptable->hash[udp_hashfn(net, ntohs(uh->dest))];
 	int dif;
 
-	read_lock(&udp_hash_lock);
-	sk = sk_head(&udptable[udp_hashfn(net, ntohs(uh->dest))]);
+	spin_lock(&hslot->lock);
+	sk = sk_head(&hslot->head);
 	dif = inet6_iif(skb);
 	sk = udp_v6_mcast_next(sk, uh->dest, daddr, uh->source, saddr, dif);
 	if (!sk) {
@@ -409,7 +421,7 @@ static int __udp6_lib_mcast_deliver(struct net *net, struct sk_buff *skb,
 		sk_add_backlog(sk, skb);
 	bh_unlock_sock(sk);
 out:
-	read_unlock(&udp_hash_lock);
+	spin_unlock(&hslot->lock);
 	return 0;
 }
 
@@ -447,7 +459,7 @@ static inline int udp6_csum_init(struct sk_buff *skb, struct udphdr *uh,
 	return 0;
 }
 
-int __udp6_lib_rcv(struct sk_buff *skb, struct hlist_head udptable[],
+int __udp6_lib_rcv(struct sk_buff *skb, struct udp_table *udptable,
 		   int proto)
 {
 	struct sock *sk;
@@ -544,7 +556,7 @@ int __udp6_lib_rcv(struct sk_buff *skb, struct hlist_head udptable[],
 
 static __inline__ int udpv6_rcv(struct sk_buff *skb)
 {
-	return __udp6_lib_rcv(skb, udp_hash, IPPROTO_UDP);
+	return __udp6_lib_rcv(skb, &udp_table, IPPROTO_UDP);
 }
 
 /*
@@ -1008,7 +1020,7 @@ int udp6_seq_show(struct seq_file *seq, void *v)
 static struct udp_seq_afinfo udp6_seq_afinfo = {
 	.name		= "udp6",
 	.family		= AF_INET6,
-	.hashtable	= udp_hash,
+	.udp_table	= &udp_table,
 	.seq_fops	= {
 		.owner	=	THIS_MODULE,
 	},
@@ -1050,7 +1062,7 @@ struct proto udpv6_prot = {
 	.sysctl_wmem	   = &sysctl_udp_wmem_min,
 	.sysctl_rmem	   = &sysctl_udp_rmem_min,
 	.obj_size	   = sizeof(struct udp6_sock),
-	.h.udp_hash	   = udp_hash,
+	.h.udp_table	   = &udp_table,
 #ifdef CONFIG_COMPAT
 	.compat_setsockopt = compat_udpv6_setsockopt,
 	.compat_getsockopt = compat_udpv6_getsockopt,

net/ipv6/udp_impl.h

@@ -7,9 +7,9 @@
 #include <net/inet_common.h>
 #include <net/transp_v6.h>
 
-extern int  	__udp6_lib_rcv(struct sk_buff *, struct hlist_head [], int );
+extern int  	__udp6_lib_rcv(struct sk_buff *, struct udp_table *, int );
 extern void 	__udp6_lib_err(struct sk_buff *, struct inet6_skb_parm *,
-			       int , int , int , __be32 , struct hlist_head []);
+			       int , int , int , __be32 , struct udp_table *);
 
 extern int	udp_v6_get_port(struct sock *sk, unsigned short snum);
 

net/ipv6/udplite.c

@@ -15,14 +15,14 @@
 
 static int udplitev6_rcv(struct sk_buff *skb)
 {
-	return __udp6_lib_rcv(skb, udplite_hash, IPPROTO_UDPLITE);
+	return __udp6_lib_rcv(skb, &udplite_table, IPPROTO_UDPLITE);
 }
 
 static void udplitev6_err(struct sk_buff *skb,
 			  struct inet6_skb_parm *opt,
 			  int type, int code, int offset, __be32 info)
 {
-	__udp6_lib_err(skb, opt, type, code, offset, info, udplite_hash);
+	__udp6_lib_err(skb, opt, type, code, offset, info, &udplite_table);
 }
 
 static struct inet6_protocol udplitev6_protocol = {
@@ -49,7 +49,7 @@ struct proto udplitev6_prot = {
 	.unhash		   = udp_lib_unhash,
 	.get_port	   = udp_v6_get_port,
 	.obj_size	   = sizeof(struct udp6_sock),
-	.h.udp_hash	   = udplite_hash,
+	.h.udp_table	   = &udplite_table,
 #ifdef CONFIG_COMPAT
 	.compat_setsockopt = compat_udpv6_setsockopt,
 	.compat_getsockopt = compat_udpv6_getsockopt,
@@ -95,7 +95,7 @@ void udplitev6_exit(void)
 static struct udp_seq_afinfo udplite6_seq_afinfo = {
 	.name		= "udplite6",
 	.family		= AF_INET6,
-	.hashtable	= udplite_hash,
+	.udp_table	= &udplite_table,
 	.seq_fops	= {
 		.owner	=	THIS_MODULE,
 	},