netdev - Re: Re-queueing of skb in vlan_skb

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Message-ID: <47FF614E.7040500@trash.net>
Date:	Fri, 11 Apr 2008 15:02:06 +0200
From:	Patrick McHardy <kaber@...sh.net>
To:	Al Viro <viro@...IV.linux.org.uk>
CC:	Brian Oostenbrink <Brian_Oostenbrink@...-sierra.com>,
	linux-net@...r.kernel.org,
	Linux Netdev List <netdev@...r.kernel.org>
Subject: Re: Re-queueing of skb in vlan_skb_recv

Al Viro wrote:
> On Fri, Apr 11, 2008 at 02:46:35PM +0200, Patrick McHardy wrote:
>> Brian Oostenbrink wrote:
>>> In vlan_skb_recv, packets are generally stripped of their vlan header,
>>> and then re-queued via netif_rx().  Is there a reason for re-queuing
>>> these instead of calling netif_receive_skb() directly?  On our system
>>> (an embedded linux router), this re-queuing has a significant
>>> performance penalty.
>> Its done to save stack space. There's currently a discussion
>> about making loopback use netif_receive_skb in case enough
>> stack is still available. Once that patch gets merged I'll
>> change VLAN in a similar way.
> 
> Another possibility would be to allow ->func() of packet_type to return an
> skb for reprocessing...


That should work fine for VLAN, but not for loopback since its
called on the TX path. I think I prefer Eric's suggested way
because it doesn't require to change all the other existing
packet_type users.

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