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authorEric Dumazet <dada1@cosmosbay.com>2007-12-17 22:45:13 -0800
committerDavid S. Miller <davem@davemloft.net>2008-01-28 14:59:10 -0800
commite2f82ac3fcffffca59751b65124544d11ed8be4a (patch)
tree9eba528eb094b79da8c471c3980c6a6b90f371b4
parent22c2d8bca212a655c120fd6617328ffa3480afad (diff)
[NETFILTER]: xt_hashlimit: speedup hash_dst()
1) Using jhash2() instead of jhash() is a litle bit faster if applicable. 2) 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: Eric Dumazet <dada1@cosmosbay.com> Signed-off-by: Patrick McHardy <kaber@trash.net> Signed-off-by: David S. Miller <davem@davemloft.net>
-rw-r--r--net/netfilter/xt_hashlimit.c11
1 files changed, 10 insertions, 1 deletions
diff --git a/net/netfilter/xt_hashlimit.c b/net/netfilter/xt_hashlimit.c
index 951d4c82967..651c1d26564 100644
--- a/net/netfilter/xt_hashlimit.c
+++ b/net/netfilter/xt_hashlimit.c
@@ -105,7 +105,16 @@ static inline bool dst_cmp(const struct dsthash_ent *ent,
static u_int32_t
hash_dst(const struct xt_hashlimit_htable *ht, const struct dsthash_dst *dst)
{
- return jhash(dst, sizeof(*dst), ht->rnd) % ht->cfg.size;
+ u_int32_t hash = jhash2((const u32 *)dst,
+ sizeof(*dst)/sizeof(u32),
+ ht->rnd);
+ /*
+ * Instead of returning hash % ht->cfg.size (implying a divide)
+ * we return the high 32 bits of the (hash * ht->cfg.size) that will
+ * give results between [0 and cfg.size-1] and same hash distribution,
+ * but using a multiply, less expensive than a divide
+ */
+ return ((u64)hash * ht->cfg.size) >> 32;
}
static struct dsthash_ent *