[NETFILTER]: xt_hashlimit: speedup hash_dst() (e2f82ac3) · Commits · 戴 / test

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>

net/netfilter/xt_hashlimit.c

+10 −1

Original line number	Diff line number	Diff line
		@@ -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 *

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