From e2f82ac3fcffffca59751b65124544d11ed8be4a Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Mon, 17 Dec 2007 22:45:13 -0800 Subject: [PATCH] [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 Signed-off-by: Patrick McHardy Signed-off-by: David S. Miller --- net/netfilter/xt_hashlimit.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-) diff --git a/net/netfilter/xt_hashlimit.c b/net/netfilter/xt_hashlimit.c index 951d4c8296..651c1d2656 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 * -- 2.39.5