linux-kernel - Re: [PATCH 4/9] AF_UNIX: find the recipients for multicast messages

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Message-Id: <20101123.103949.39186245.davem@davemloft.net>
Date:	Tue, 23 Nov 2010 10:39:49 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	alban.crequy@...labora.co.uk
Cc:	eric.dumazet@...il.com, shemminger@...tta.com, gorcunov@...nvz.org,
	adobriyan@...il.com, lennart@...ttering.net, kay.sievers@...y.org,
	ian.molton@...labora.co.uk, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/9] AF_UNIX: find the recipients for multicast messages

From: Alban Crequy <alban.crequy@...labora.co.uk>
Date: Tue, 23 Nov 2010 17:47:01 +0000

> Le Tue, 23 Nov 2010 17:08:37 +0100,
> Eric Dumazet <eric.dumazet@...il.com> a écrit :
>> 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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