netdev - Re: [patch net-next-2.6] net: vlan: make non-hw-accel rx path similar to hw-accel

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Date:	Mon, 04 Apr 2011 12:51:51 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Nicolas de Pesloüan <nicolas.2p.debian@...il.com>
Cc:	Jiri Pirko <jpirko@...hat.com>, Jesse Gross <jesse@...nel.org>,
	netdev@...r.kernel.org, davem@...emloft.net,
	shemminger@...ux-foundation.org, kaber@...sh.net, fubar@...ibm.com,
	eric.dumazet@...il.com, andy@...yhouse.net, xiaosuo@...il.com
Subject: Re: [patch net-next-2.6] net: vlan: make non-hw-accel rx path similar to hw-accel

Nicolas de Pesloüan <nicolas.2p.debian@...il.com> writes:

> Le 04/04/2011 09:14, Jiri Pirko a écrit :
>> Mon, Apr 04, 2011 at 08:54:40AM CEST, nicolas.2p.debian@...il.com wrote:
>>> Le 03/04/2011 22:38, Jesse Gross a écrit :
> <snip>
>>>> It would be nice to merge all of this together.  One complication is
>>>> the interaction of bridging and vlan on the same device.  Some people
>>>> want to have a bridge for each vlan and a bridge for untagged packets.
>>>>   On older kernels with vlan accelerated hardware this was possible
>>>> because vlan devices would get packets before bridging and on current
>>>> kernels it is possible with ebtables rules.  If we use rx_handler for
>>>> both I believe we would need to extend it some to allow multiple
>>>> handlers.
>>>
>>> I totally agree.
>>
>> I do not. The reason I do vlan_untag early is so actually emulates
>> hw acceleration. The reason is to make rx path of hwaccel an
>> nonhwaccel similar. If you move vlan untag to rx_handler, this goal
>> wouldn't be achieved.
>
> Need to think more about that point.
>
>>> Remember that Jiri's original proposal (last summer) was to have
>>> several rx_handlers per net_device. I still think we need several of
>>> them, because the network stack need to be generic and allow for any
>>> complex stacking setup. The rx_handler framework may need to be
>>> enhanced for that, but I think it is the right tool to do all those
>>> per net_device specific features.
>>>
>>>>> This would also cause protocol handlers to receive the untouched (tagged)
>>>>> frame, if no setup required the frame to be untagged, which I think is the
>>>>> right thing to do.
>>>>
>>>> At the very least we need to make sure that these packets are marked
>>>> as PACKET_OTHERHOST because protocol handlers don't pay attention to
>>>> the vlan field.
>>>
>>> Agreed.
>>>
>>>>>> @@ -3177,7 +3183,7 @@ ncls:
>>>>>>                        ret = deliver_skb(skb, pt_prev, orig_dev);
>>>>>>                        pt_prev = NULL;
>>>>>>                }
>>>>>> -             if (vlan_hwaccel_do_receive(&skb)) {
>>>>>> +             if (vlan_do_receive(&skb)) {
>>>>>>                        ret = __netif_receive_skb(skb);
>>>>>>                        goto out;
>>>>>>                } else if (unlikely(!skb))
>>>>>
>>>>> Why are you calling __netif_receive_skb here? Can't we simply goto
>>>>> another_round?
>>>>
>>>> This code (other than the name change) predates the
>>>> another_round/rx_handler changes.
>>>
>>> Yes, you are right. Let's keep this for a possible follow-up patch,
>>> to avoid skb reinjection when it is not strictly necessary.
>>
>> To do another round here was my attention do do in follow up patch (I'm
>> still figuring out how to move this effectively into rx_handlers)
>
> So you want to move vlan_do_receive into an rx_handler, but want untagging to
> stay hard-coded at the beginning of __netif_receive_skb. I don't think I
> understand the rational behind that.

__netif_receive_skb is actually late for untagging.  eth_type_trans
would be better but not path of control into __netif_receive_skb
actually calls eth_type_trans.

Eric

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