netdev - Re: [NETFILTER] xt_hashlimit : speedups hash

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Message-ID: <476266FF.4080300@trash.net>
Date:	Fri, 14 Dec 2007 12:20:31 +0100
From:	Patrick McHardy <kaber@...sh.net>
To:	Eric Dumazet <dada1@...mosbay.com>
CC:	netfilter-devel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [NETFILTER] xt_hashlimit : speedups hash_dst()

Eric Dumazet wrote:
> 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.


Clever :) Applied, thanks Eric.

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