netdev - Re: [RFC PATCH v0 1/2] net: bridge: propagate FDB table into hardware

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Date:	Thu, 09 Feb 2012 12:30:36 -0800
From:	John Fastabend <john.r.fastabend@...el.com>
To:	Sridhar Samudrala <sri@...ibm.com>
CC:	bhutchings@...arflare.com, roprabhu@...co.com,
	netdev@...r.kernel.org, mst@...hat.com, chrisw@...hat.com,
	davem@...emloft.net, gregory.v.rose@...el.com,
	shemminger@...tta.com, kvm@...r.kernel.org
Subject: Re: [RFC PATCH v0 1/2] net: bridge: propagate FDB table into hardware

On 2/9/2012 10:14 AM, Sridhar Samudrala wrote:
> On Wed, 2012-02-08 at 19:22 -0800, John Fastabend wrote:
>> Propagate software FDB table into hardware uc, mc lists when
>> the NETIF_F_HW_FDB is set.
>>
>> This resolves the case below where an embedded switch is used
>> in hardware to do inter-VF or VF-PF switching. This patch
>> pushes the FDB entry (specifically the MAC address) into the
>> embedded switch with dev_add_uc and dev_add_mc so the switch
>> "learns" about the software bridge.
>>
>>
>>           veth0  veth2
>>             |      |
>>           ------------
>>           |  bridge0 |   <---- software bridging
>>           ------------
>>                /
>>                /
>>   ethx.y      ethx
>>     VF         PF
>>      \         \          <---- propagate FDB entries to HW
>>      \         \
>>   --------------------
>>   |  Embedded Bridge |    <---- hardware offloaded switching
>>   --------------------
>>
> 
> This scenario works now as adding an interface to a bridge puts it in
> promiscuous mode. So adding a PF to a software bridge should not be
> a problem as it supports promiscuous mode. But adding a VF will not
> work.

It shouldn't work because the embedded bridge will lookup the address
in its FDB and when it doesn't match any unicast filters it will forward
the packet onto the wire. Because the veth0 and veth2 above never get
inserted into the embedded brdige's FDB the packets will _never_ get
routed there.

That said the current 'ixgbe' driver is doing something broken in that
it is always setting the unicast hash table and mirroring bits to 1. So
if you think this is working your seeing a bug where packets are being
sent onto the wire AND upto the PF. Packets with destination addresses
matching veth1 should not end up on the wire and vice versa. This is
specific to ixgbe and is not the case for other SR-IOV devices.

This causes some issues (a) has some very real performance implications,
(b) at this point you have some strange behavior from my point of view.
The embedded bridge is not a learning bridge nor is it acting like an
802.1Q VEB or VEPA.

> 
> Are you trying to avoid the requirement of having to put the interface 
> in promiscuous mode when adding to a bridge?
> 

I think the bridge being in promiscuous mode is correct.

Hope that helps sorry its a bit long winded.
John

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