Date: Tue, 23 Nov 2010 10:39:49 -0800 (PST)
Message-Id: <20101123.103949.39186245.davem@davemloft.net>
To: alban.crequy@collabora.co.uk
Cc: eric.dumazet@gmail.com, shemminger@vyatta.com, gorcunov@openvz.org,
        adobriyan@gmail.com, lennart@poettering.net, kay.sievers@vrfy.org,
        ian.molton@collabora.co.uk, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH 4/9] AF_UNIX: find the recipients for multicast messages
From: David Miller <davem@davemloft.net>
In-Reply-To: <20101123174701.1b2f6f16@chocolatine.cbg.collabora.co.uk>
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	<1290528517.3046.91.camel@edumazet-laptop>
	<20101123174701.1b2f6f16@chocolatine.cbg.collabora.co.uk>
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From: Alban Crequy <alban.crequy@collabora.co.uk>
Date: Tue, 23 Nov 2010 17:47:01 +0000

> Le Tue, 23 Nov 2010 17:08:37 +0100,
> Eric Dumazet <eric.dumazet@gmail.com> a ?crit :
>> I am not sure if doing 90 clones of skb and filtering them one by one
>> is going to be fast :-(
> 
> Yes... I think it can be optimized. Run the socket filter first by
> calling sk_run_filter() directly and then call skb_clone() + pskb_trim()
> only on the few remaining sockets.

BTW, we have and have talked about the same exact problem with
AF_PACKET socket users such as DHCP.

We clone and push the packet down into the AF_PACKET protocol
code from the pt_type callback when %99 of the time the socket
filter doesn't match and thus the clone is completely wasted
work.

If we know the socket, or more specifically the filter, early enough,
we could have a special interface like:

	struct sk_buff *skb_filter_or_clone(struct sk_buff *skb, ...)

Which returns a non-NULL cloned SKB if the filter accepts the
packet.
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