[INET]: speedup inet (tcp/dccp) lookups

Arnaldo and I agreed it could be applied now, because I have other
pending patches depending on this one (Thank you Arnaldo)

(The other important patch moves skc_refcnt in a separate cache line,
so that the SMP/NUMA performance doesnt suffer from cache line ping pongs)

1) First some performance data :
--------------------------------

tcp_v4_rcv() wastes a *lot* of time in __inet_lookup_established()

The most time critical code is :

sk_for_each(sk, node, &head->chain) {
     if (INET_MATCH(sk, acookie, saddr, daddr, ports, dif))
         goto hit; /* You sunk my battleship! */
}

The sk_for_each() does use prefetch() hints but only the begining of
"struct sock" is prefetched.

As INET_MATCH first comparison uses inet_sk(__sk)->daddr, wich is far
away from the begining of "struct sock", it has to bring into CPU
cache cold cache line. Each iteration has to use at least 2 cache
lines.

This can be problematic if some chains are very long.

2) The goal
-----------

The idea I had is to change things so that INET_MATCH() may return
FALSE in 99% of cases only using the data already in the CPU cache,
using one cache line per iteration.

3) Description of the patch
---------------------------

Adds a new 'unsigned int skc_hash' field in 'struct sock_common',
filling a 32 bits hole on 64 bits platform.

struct sock_common {
	unsigned short		skc_family;
	volatile unsigned char	skc_state;
	unsigned char		skc_reuse;
	int			skc_bound_dev_if;
	struct hlist_node	skc_node;
	struct hlist_node	skc_bind_node;
	atomic_t		skc_refcnt;
+	unsigned int		skc_hash;
	struct proto		*skc_prot;
};

Store in this 32 bits field the full hash, not masked by (ehash_size -
1) Using this full hash as the first comparison done in INET_MATCH
permits us immediatly skip the element without touching a second cache
line in case of a miss.

Suppress the sk_hashent/tw_hashent fields since skc_hash (aliased to
sk_hash and tw_hash) already contains the slot number if we mask with
(ehash_size - 1)

File include/net/inet_hashtables.h

64 bits platforms :
#define INET_MATCH(__sk, __hash, __cookie, __saddr, __daddr, __ports, __dif)\
     (((__sk)->sk_hash == (__hash))
     ((*((__u64 *)&(inet_sk(__sk)->daddr)))== (__cookie))   &&  \
     ((*((__u32 *)&(inet_sk(__sk)->dport))) == (__ports))   &&  \
     (!((__sk)->sk_bound_dev_if) || ((__sk)->sk_bound_dev_if == (__dif))))

32bits platforms:
#define TCP_IPV4_MATCH(__sk, __hash, __cookie, __saddr, __daddr, __ports, __dif)\
     (((__sk)->sk_hash == (__hash))                 &&  \
     (inet_sk(__sk)->daddr          == (__saddr))   &&  \
     (inet_sk(__sk)->rcv_saddr      == (__daddr))   &&  \
     (!((__sk)->sk_bound_dev_if) || ((__sk)->sk_bound_dev_if == (__dif))))


- Adds a prefetch(head->chain.first) in 
__inet_lookup_established()/__tcp_v4_check_established() and 
__inet6_lookup_established()/__tcp_v6_check_established() and 
__dccp_v4_check_established() to bring into cache the first element of the 
list, before the {read|write}_lock(&head->lock);

Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>
Acked-by: Arnaldo Carvalho de Melo <acme@ghostprotocols.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 10 insertions, 8 deletions

diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
index 80643e6b346..d693cb988b7 100644
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c
@@ -209,9 +209,11 @@ static __inline__ void __tcp_v6_hash(struct sock *sk)
 		lock = &tcp_hashinfo.lhash_lock;
 		inet_listen_wlock(&tcp_hashinfo);
 	} else {
-		sk->sk_hashent = inet6_sk_ehashfn(sk, tcp_hashinfo.ehash_size);
-		list = &tcp_hashinfo.ehash[sk->sk_hashent].chain;
-		lock = &tcp_hashinfo.ehash[sk->sk_hashent].lock;
+		unsigned int hash;
+		sk->sk_hash = hash = inet6_sk_ehashfn(sk);
+		hash &= (tcp_hashinfo.ehash_size - 1);
+		list = &tcp_hashinfo.ehash[hash].chain;
+		lock = &tcp_hashinfo.ehash[hash].lock;
 		write_lock(lock);
 	}
 
@@ -322,13 +324,13 @@ static int __tcp_v6_check_established(struct sock *sk, const __u16 lport,
 	const struct in6_addr *saddr = &np->daddr;
 	const int dif = sk->sk_bound_dev_if;
 	const u32 ports = INET_COMBINED_PORTS(inet->dport, lport);
-	const int hash = inet6_ehashfn(daddr, inet->num, saddr, inet->dport,
-				       tcp_hashinfo.ehash_size);
-	struct inet_ehash_bucket *head = &tcp_hashinfo.ehash[hash];
+	unsigned int hash = inet6_ehashfn(daddr, inet->num, saddr, inet->dport);
+	struct inet_ehash_bucket *head = inet_ehash_bucket(&tcp_hashinfo, hash);
 	struct sock *sk2;
 	const struct hlist_node *node;
 	struct inet_timewait_sock *tw;
 
+	prefetch(head->chain.first);
 	write_lock(&head->lock);
 
 	/* Check TIME-WAIT sockets first. */
@@ -365,14 +367,14 @@ static int __tcp_v6_check_established(struct sock *sk, const __u16 lport,
 
 	/* And established part... */
 	sk_for_each(sk2, node, &head->chain) {
-		if (INET6_MATCH(sk2, saddr, daddr, ports, dif))
+		if (INET6_MATCH(sk2, hash, saddr, daddr, ports, dif))
 			goto not_unique;
 	}
 
 unique:
 	BUG_TRAP(sk_unhashed(sk));
 	__sk_add_node(sk, &head->chain);
-	sk->sk_hashent = hash;
+	sk->sk_hash = hash;
 	sock_prot_inc_use(sk->sk_prot);
 	write_unlock(&head->lock);