linux-kernel - Re: [PATCH] Update jhash.h with the new version of Jenkins' hash

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Message-ID: <Pine.LNX.4.64.0902181345010.31742@wrl-59.cs.helsinki.fi>
Date:	Wed, 18 Feb 2009 13:50:43 +0200 (EET)
From:	"Ilpo Järvinen" <ilpo.jarvinen@...sinki.fi>
To:	Jozsef Kadlecsik <kadlec@...ckhole.kfki.hu>
cc:	Kyle Moffett <kyle@...fetthome.net>,
	LKML <linux-kernel@...r.kernel.org>,
	Netdev <netdev@...r.kernel.org>, netfilter-devel@...r.kernel.org,
	Rusty Russell <rusty@...tcorp.com.au>
Subject: Re: [PATCH] Update jhash.h with the new version of Jenkins' hash

On Tue, 17 Feb 2009, Jozsef Kadlecsik wrote:

> On Thu, 12 Feb 2009, Rusty Russell wrote:
> 
> > My concern was that it's also bigger (and we inline it).  Performance is
> > pretty much a wash since we so rarely hash more than a few words.
> 
> In netfilter/conntrack (;-) we call the hash function for every packet, so 
> even if a small number of cycle can be gained at one lookup, I think it's 
> worth. And in the IPv4/IPv6 neutral nf_conntrack we hash 9 words.

FYI, I once looked into inlining cost and jhash functions were among the 
most wasteful (kernel-wide). Multiple jhash bodies were 100+ bytes, and 
the overall cost was 10k+. I never got to the final submit of the 
uninlining patch though...


-- 
 i.
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