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Commit e2f82ac3 authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller
Browse files

[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: default avatarEric Dumazet <dada1@cosmosbay.com>
Signed-off-by: default avatarPatrick McHardy <kaber@trash.net>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 22c2d8bc

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 *