From: Eric Dumazet <dada1@xxxxxxxxxxxxx> Date: Fri, 14 Dec 2007 12:09:31 +0100 > 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@xxxxxxxxxxxxx> As a side note, Jenkins performs nearly optimally (unlike most traditional hash functions) with power of two hash table sizes. Using a pow2 hash table size would completely obviate the issues solved by #2. I don't know if that is feasible here in xt_hashlimit, but if it is that is how we should solve this expensive modulo. - To unsubscribe from this list: send the line "unsubscribe netfilter-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
