From: Pablo Neira Ayuso <pablo@netfilter.org>
To: Eric Dumazet <eric.dumazet@gmail.com>
Cc: David Laight <David.Laight@ACULAB.COM>,
netfilter-devel@vger.kernel.org, davem@davemloft.net,
netdev@vger.kernel.org
Subject: Re: [PATCH 3/7] netfilter: xt_HMARK: modulus is expensive for hash calculation
Date: Thu, 17 May 2012 16:55:50 +0200 [thread overview]
Message-ID: <20120517145550.GA6501@1984> (raw)
In-Reply-To: <1337243968.3403.3.camel@edumazet-glaptop>
On Thu, May 17, 2012 at 10:39:28AM +0200, Eric Dumazet wrote:
> On Thu, 2012-05-17 at 09:16 +0100, David Laight wrote:
> > > From: Pablo Neira Ayuso <pablo@netfilter.org>
> > >
> > > Use:
> > >
> > > ((u64)(HASH_VAL * HASH_SIZE)) >> 32
> > >
> > > as suggested by David S. Miller.
> >
> > That (u64) cast is very unlikely to have any effect.
> > If you want a 64 bit result from the product of two
> > 32 bit values, you have to cast one of the 32 bit values
> > prior to the multiply - as in the patch below.
>
> Hey, Changelog is a bit wrong (for several reasons) but code is correct.
>
> return (((u64)hash * info->hmodulus) >> 32) + info->hoffset;
Sorry, for the mistake in the changelog. I copied & pasted it from the
mailing list discussion.
next prev parent reply other threads:[~2012-05-17 14:55 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-05-16 23:06 [PATCH 0/7] netfilter updates for net-next (batch 3) pablo
2012-05-16 23:06 ` [PATCH 1/7] netfilter: xt_hashlimit: use _ALL macro to reject unknown flag bits pablo
2012-05-16 23:06 ` [PATCH 2/7] netfilter: xt_HMARK: potential NULL dereference in get_inner_hdr() pablo
2012-05-16 23:06 ` [PATCH 3/7] netfilter: xt_HMARK: modulus is expensive for hash calculation pablo
2012-05-17 8:16 ` David Laight
2012-05-17 8:39 ` Eric Dumazet
2012-05-17 14:55 ` Pablo Neira Ayuso [this message]
2012-05-16 23:06 ` [PATCH 4/7] netfilter: nf_ct_tcp: extend log message for invalid ignored packets pablo
2012-05-16 23:06 ` [PATCH 5/7] netfilter: ipset: fix timeout value overflow bug pablo
2012-05-16 23:06 ` [PATCH 6/7] netfilter: xt_CT: remove redundant header include pablo
2012-05-16 23:06 ` [PATCH 7/7] netfilter: nf_ct_h323: fix usage of MODULE_ALIAS_NFCT_HELPER pablo
2012-05-17 0:00 ` [PATCH 0/7] netfilter updates for net-next (batch 3) David Miller
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