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

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 <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 8 insertions, 4 deletions

diff --git a/net/ipv4/netfilter/ipt_CLUSTERIP.c b/net/ipv4/netfilter/ipt_CLUSTERIP.c
index a48e26449fd5..df39ca07fb12 100644
--- a/net/ipv4/netfilter/ipt_CLUSTERIP.c
+++ b/net/ipv4/netfilter/ipt_CLUSTERIP.c
@@ -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
diff --git a/net/ipv4/netfilter/nf_nat_core.c b/net/ipv4/netfilter/nf_nat_core.c
index aec157d0ad93..e53ae1ef8f5e 100644
--- a/net/ipv4/netfilter/nf_nat_core.c
+++ b/net/ipv4/netfilter/nf_nat_core.c
@@ -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,