netdev - Re: [patch net-next-2.6] net: convert bonding to use rx

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Date:	Fri, 18 Feb 2011 19:47:26 +0100
From:	Jiri Pirko <jpirko@...hat.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Patrick McHardy <kaber@...sh.net>, netdev@...r.kernel.org,
	davem@...emloft.net, shemminger@...ux-foundation.org,
	fubar@...ibm.com, nicolas.2p.debian@...il.com, andy@...yhouse.net
Subject: Re: [patch net-next-2.6] net: convert bonding to use rx_handler

Fri, Feb 18, 2011 at 05:14:30PM CET, eric.dumazet@...il.com wrote:
>Le vendredi 18 février 2011 à 16:50 +0100, Patrick McHardy a écrit :
>> On 18.02.2011 15:58, Jiri Pirko wrote:
>> > Fri, Feb 18, 2011 at 03:46:45PM CET, kaber@...sh.net wrote:
>> >> Am 18.02.2011 15:27, schrieb Eric Dumazet:
>> >>> Le vendredi 18 février 2011 à 15:14 +0100, Jiri Pirko a écrit :
>> >>>
>> >>>> Do not know how to do it better. As for percpu variable, not only
>> >>>> origdev would have to be remembered but also probably skb pointer to
>> >>>> know if it's the first run on the skb or not. Can't really figure out a
>> >>>> better solution. Can you?
>> >>>
>> >>> I'll try and let you know.
>> >>
>> >> Why not simply do a lookup on skb->iif?
>> > 
>> > Well I was trying to avoid iterating over list of devices for each
>> > incoming frame.
>> > 
>> 
>> Well, there are a couple of holes on 64 bit, perhaps you can rearrange
>> things and eliminate either iif or input_dev without increasing size
>> since they appear to be redundant.
>
>Jiri
>
>I dont understand why netif_rx() is needed in your patch.

I used netif_rx() because bridge and macvlan does that too. I did not see
a reason to not to do the same.

>
>Can we stack 10 bond devices or so ???
>
>If we avoid this stage and call the real thing (netif_receive_skb()),
>then we dont need adding a field in each skb, since it can be carried by
>a global variable (per cpu of course)
>
I'm probably missing something. How do netif_receive_skb() and
netif_rx() differ in this point of view, since both are calling:
"ret = enqueue_to_backlog(skb, cpu, &rflow->last_qtail);"
?

Still I see a problem with the percpu global variable. We would have to
store skb pointer there as well and in each __netif_receive_skb() call it
would have to be checked if it's different from the current one.
In that case store new skb and orig_Dev.

Leaving aside that global variables are evil in general, I still think
this is not nicer solution then to add skb->input_dev (although I
understand your arguments).


>bond_handle_frame() being called from __netif_receive_skb() I believe it
>can use netif_receive_skb() instead of netif_rx().
>
>Same remark for vlan_on_bond_hook()
>
>
>
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