netdev - Re: [patch net-next-2.6] bonding: remove skb_share_check in handle

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Message-ID: <4D6EBC7B.8040502@gmail.com>
Date:	Wed, 02 Mar 2011 22:54:03 +0100
From:	Nicolas de Pesloüan 
	<nicolas.2p.debian@...il.com>
To:	Jiri Pirko <jpirko@...hat.com>
CC:	Andy Gospodarek <andy@...yhouse.net>, netdev@...r.kernel.org,
	davem@...emloft.net, fubar@...ibm.com, eric.dumazet@...il.com
Subject: Re: [patch net-next-2.6] bonding: remove skb_share_check in handle_frame

Le 02/03/2011 22:12, Jiri Pirko a écrit :
> Wed, Mar 02, 2011 at 09:47:50PM CET, nicolas.2p.debian@...il.com wrote:
>> Hi Jiri,
>>
>> Do you plan to call the bonding ARP handler from inside bond_handle_frame()?
>
> I do - it's part of patchset I've cooked (going to test that tomorrow).
>
>> A few days ago
>> (http://marc.info/?l=linux-netdev&m=129883949022340&w=2), I noticed
>> that it is not possible to call the bonding ARP handler from inside
>> the bonding rx_handler, because some frame processing may be required
>> after the bonding rx_handler call, to put the frame in a suitable
>> state for the bonding ARP handler.
>
> Do you see another scenario besides the next one?

None that currently work, but eth0 -> bond0 -> br0 -> br0.100 should work too.

>> This is at least true with the following setup, eth0 ->  bond0 ->
>> bond0.100, where the ARP frames are VLAN tagged at the time the
>> bonding rx_handler process them.
>
> Isn't this scenario resolved by vlan_on_bond_hook ?
>
> eth0
>    ->rx_handler ->  another round
> bond0
>    ->vlan_hwaccel_do_receive ->  __netif_receive_skb
> bond0.100
>    ->vlan_on_bond_hook ->  reinject to bond0

Yes, it is, but this hack does not solve the eth0 -> bond0 -> br0 -> br0.100 configuration.

All those handlers that call netif_rx() or __netif_receive_skb() sound horrible to me. Can you 
imagine the global overhead of the above receive path?

The reason why I suggested you introduce the goto another_round is because most - if not all - 
stacking configurations could/should be handled simply by returning the right skb from the 
rx_handler and let __netif_receive_skb() loop. And by having the right orig_dev logic inside 
__netif_receive_skb(), it could be possible to remove the current vlan_on_bond_hook hack.

My question about whether the skb is shared between the protocol handlers (in another thread) also 
target at this idea.

You will probably told me I'm free to propose patchs for all that, and you are right. Just missing 
the time to do so.

	Nicolas.
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