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, 7 insertions, 6 deletions

diff --git a/net/ipv4/udplite.c b/net/ipv4/udplite.c
index 3c80796..d8ea8e5 100644
--- a/net/ipv4/udplite.c
+++ b/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 @@ out_register_err:
 	printk(KERN_CRIT "%s: Cannot add UDP-Lite protocol.\n", __func__);
 }
 
-EXPORT_SYMBOL(udplite_hash);
 EXPORT_SYMBOL(udplite_prot);