netdev - Re: [PATCH] NET : change layout of ehash table

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Message-ID: <p73zm7n1ygk.fsf@bingen.suse.de>
Date:	09 Feb 2007 10:18:03 +0100
From:	Andi Kleen <ak@...e.de>
To:	David Miller <davem@...emloft.net>
Cc:	dada1@...mosbay.com, linux@...izon.com, akepner@....com,
	netdev@...r.kernel.org
Subject: Re: [PATCH] NET : change layout of ehash table

David Miller <davem@...emloft.net> writes:
> 
> I've applied this, but I _REALLY_ don't like the new multiply
> instructions that are used now in the hash indexing paths when
> CONFIG_SMP is set.
> 
> I think that's a higher cost than the memory waste.

You're serious? multiply on a modern CPU is _much_ cheaper than a cache miss
e.g. a K8 can do a arbitary 64bit multiplication in 3-7 cycles.
Any cache miss will be in the three to four digits at least.

-Andi
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