netdev - Re: [patch net-next] ipv6: allow userspace to create address with IFLA_F

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Date:	Wed, 6 Nov 2013 13:03:39 +0100
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	David Laight <David.Laight@...LAB.COM>
Cc:	nicolas.dichtel@...nd.com, David Miller <davem@...emloft.net>,
	jiri@...nulli.us, vyasevich@...il.com, netdev@...r.kernel.org,
	kuznet@....inr.ac.ru, jmorris@...ei.org, yoshfuji@...ux-ipv6.org,
	kaber@...sh.net, thaller@...hat.com, stephen@...workplumber.org
Subject: Re: [patch net-next] ipv6: allow userspace to create address with IFLA_F_TEMPORARY flag

On Wed, Nov 06, 2013 at 09:23:05AM -0000, David Laight wrote:
> > By the way:
> > Although dhclient uses an AF_PACKET socket, it never does request
> > additional multicast addresses or promisc mode. So the only overhead is
> > that we have to run the socket filter on each incoming packet.
> 
> Just creating the AF_PACKET socket requires that every receive
> frame be duplicated.
> On Linux this is a reference counted but the cost is still non-zero.
> On some other OS (I first saw this with VxWorks) it is a full data copy.

Yes, I saw that, so my guess was that running the filter on every incoming UDP
packet would be the highes cost factor (it still does get filtered by protocol
number early in the stack).

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