Subject: Re: [RFC PATCH net-next v2 1/1] net: Support for switch port configuration

From: Roopa Prabhu <[email-masked]>
Date: Fri, 19 Dec 2014 08:22:40 -0800

On 12/19/14, 1:55 AM, Jiri Pirko wrote:
> Fri, Dec 19, 2014 at 10:35:27AM CET, [email-masked] wrote:
>> On 19 December 2014 at 14:53, Jiri Pirko <[email-masked]> wrote:
>>> Fri, Dec 19, 2014 at 10:01:46AM CET, [email-masked] wrote:
>>>> On 19 December 2014 at 13:57, Jiri Pirko <[email-masked]> wrote:
>>>>> Fri, Dec 19, 2014 at 06:14:57AM CET, [email-masked] wrote:
>>>>>> On 19 December 2014 at 05:18, Roopa Prabhu <[email-masked]> wrote:
>>>>>>> On 12/18/14, 3:26 PM, Samudrala, Sridhar wrote:
>>>> <snipped for ease of reading>
>>>>>>>>
>>>>>>>> We also need an interface to set per-switch attributes. Can this work?
>>>>>>>>      bridge link set dev sw0 sw_attr bcast_flooding 1 master
>>>>>>>> where sw0 is a bridge representing the hardware switch.
>>>>>>>
>>>>>>> Not today. We discussed this @ LPC, and one way to do this would be to have
>>>>>>> a device
>>>>>>> representing the switch asic. This is in the works.
>>>>>>
>>>>>> Can I assume that on  platforms which house more than one asic (say
>>>>>> two 24 port asics, interconnected via a 10G link or equivalent, to get
>>>>>> a 48 port 'switch') , the 'rocker' driver (or similar) should expose
>>>>>> them as a single set of ports, and not as two 'switch ports' ?
>>>>> Well that really depends on particular implementation and drivers. If you
>>>>> have 2 pci-e devices, I think you should expose them as 2 entities. For
>>>>> sure, you can have the driver to do the masking for you. I don't believe
>>>>> that is correct though.
>>>>>
>>>> In a platform that houses two asic chips, IMO, the user is still
>>>> expected to manage the router as a single entity. The configuration
>>>> being applied on both asic devices need to be matching if not
>>>> identical, and may not be conflicting. The FDB is to be synchronized
>>>> so that (offloaded) switching can happen across the asics. Some of
>>>> this stuff is asic specific anyway. Another example is that of the
>>>> learning. The (hardware) learning can't be enabled on one asic, while
>>>> being disabled on another one. The general use cases I have seen are
>>>> all involving managing the 'router' as a single entity.  That the
>>>> 'router' is implemented with two asics instead of a single asic (with
>>>> more ports) is to be treated as an implementation detail.  This is the
>>>> usual router management method that exists today.
>>>>
>>>> I hope I make sense.
>>>>
>>>> So I am trying to figure out what this single entity that will be used
>>> >from a user perspective. It can be a bridge, but our bridges are more
>>>> 802.1q bridges. We can use the 'self' mode, but then it means that it
>>>> should reflect the entire port count, and not just an asic.
>>>>
>>>> So I was trying to deduce that in our switchdevice model, the best bet
>>>> would be to leave the unification to the driver (i.e., to project the
>>>> multiple physical asics as a single virtual switch device). Thist
>>> Is it possible to have the asic as just single one? Or is it possible to
>>> connect asics being multiple chips maybe from multiple vendors together?
>> I didn't understand the first question. Some times, it is possible to
> I ment that there is a design with just a single asic of this type,
> instead of a pair.
>
>> have a single asic replace two, but its a cost factor, and others that
>> are involved.
>>
>> AFAIK, the answer to the second question is a No. Two asics from
>> different vendors may not be connected together. The interconnect
>> tends to be proprietary.
> Okay. In that case, it might make sense to mask it on driver level.
>
>
>>> I believe that answer is "yes" in both cases. Making two separate asics
>>> to appear as one for user is not correct in my opinion. Driver should
>>> not do such masking. It is unclean, unextendable.
>>>
>> I am only looking for a single management entity. I am not thinking it
>> needs to be at driver level. I am not sure of  any other option apart
> >from creating a 'switchdev' that Roopa was mentioning.
>
> Well the thing is there is a common desire to make the offloading as
> transparent as possible. For example, have 4 ports of same switch and
> put them into br0. Just like that, without need to do anything else
> than you would do when bridging ordinary NICs. Introducing some
> "management entity" would break this approach.
>
I don't think having a switchdevice breaks this approach. A software 
bridge is not a 1-1 mapping with the asic in all cases.
When its a vlan filtering bridge, yes, it is (In which case all switch 
global l2 non-port specific attributes can be applied to the bridge).

The switch asic can do l2 and l3 too. For a bridge, the switch asic is 
just accelerating l2.
And a switch asic is also capable of l3, acls. A switch device (whether 
accessible to userspace or not)
may become necessary (as discussed in other threads) where you cannot 
resolve a kernel object to a switch port (Global acl rules, unresolved 
route nexthops etc).