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, 4 Apr 2011 22:30:02 +0200
From:	Jiri Pirko <jpirko@...hat.com>
To:	Nicolas de Pesloüan 
	<nicolas.2p.debian@...il.com>
Cc:	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,
	"Eric W. Biederman" <ebiederm@...ssion.com>
Subject: Re: [patch net-next-2.6] net: vlan: make non-hw-accel rx path
 similar to hw-accel

Mon, Apr 04, 2011 at 09:00:00PM CEST, nicolas.2p.debian@...il.com wrote:
>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.

vlan_hwaccel_do_receive/vlan_do_receive could be converted to
rx_handler, not untagging.

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