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, 2 insertions, 2 deletions

diff --git a/net/ipv4/udp_impl.h b/net/ipv4/udp_impl.h
index 2e9bad2..9f4a616 100644
--- a/net/ipv4/udp_impl.h
+++ b/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);