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[NETFILTER]: non-power-of-two jhash optimizations

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Apply Eric Dumazet's jhash optimizations where applicable. Quoting Eric:

Thanks to jhash, hash value uses full 32 bits. Instead of returning
hash % size (implying a divide) we return the high 32 bits of the
(hash * size) that will give results between [0 and size-1] and same
hash distribution.

On most cpus, a multiply is less expensive than a divide, by an order
of magnitude.

Signed-off-by: Patrick McHardy <[email protected]>
Signed-off-by: David S. Miller <[email protected]>
This commit is contained in:
Patrick McHardy 2007-12-17 22:45:52 -08:00 • committed by David S. Miller
commit 34498825cb
4 changed files with 14 additions and 8 deletions
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2
net/ipv4/netfilter/ipt_CLUSTERIP.c
View file

@ -273,7 +273,7 @@ clusterip_hashfn(const struct sk_buff *skb,
}
/* node numbers are 1..n, not 0..n */
return (hashval % config->num_total_nodes) + 1;
return (((u64)hashval * config->num_total_nodes) >> 32) + 1;
}
static inline int

10
net/ipv4/netfilter/nf_nat_core.c
View file

@ -77,10 +77,13 @@ EXPORT_SYMBOL_GPL(nf_nat_proto_put);
static inline unsigned int
hash_by_src(const struct nf_conntrack_tuple *tuple)
{
unsigned int hash;
/* Original src, to ensure we map it consistently if poss. */
return jhash_3words((__force u32)tuple->src.u3.ip,
hash = jhash_3words((__force u32)tuple->src.u3.ip,
(__force u32)tuple->src.u.all,
tuple->dst.protonum, 0) % nf_nat_htable_size;
tuple->dst.protonum, 0);
return ((u64)hash * nf_nat_htable_size) >> 32;
}
/* Is this tuple already taken? (not by us) */
@ -211,7 +214,8 @@ find_best_ips_proto(struct nf_conntrack_tuple *tuple,
maxip = ntohl(range->max_ip);
j = jhash_2words((__force u32)tuple->src.u3.ip,
(__force u32)tuple->dst.u3.ip, 0);
*var_ipp = htonl(minip + j % (maxip - minip + 1));
j = ((u64)j * (maxip - minip + 1)) >> 32;
*var_ipp = htonl(minip + j);
}
/* Manipulate the tuple into the range given. For NF_INET_POST_ROUTING,