netdev - Re: [patch net-next RFC 0/2] fib4 offload: notifier to let hw to be aware of all prefixes

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Date:   Mon, 19 Sep 2016 17:15:49 +0200
From:   Jiri Pirko <jiri@...nulli.us>
To:     Roopa Prabhu <roopa@...ulusnetworks.com>
Cc:     Florian Fainelli <f.fainelli@...il.com>, netdev@...r.kernel.org,
        davem@...emloft.net, idosch@...lanox.com, eladr@...lanox.com,
        yotamg@...lanox.com, nogahf@...lanox.com, ogerlitz@...lanox.com,
        nikolay@...ulusnetworks.com, linville@...driver.com, tgraf@...g.ch,
        gospo@...ulusnetworks.com, sfeldma@...il.com, ast@...mgrid.com,
        edumazet@...gle.com, hannes@...essinduktion.org,
        dsa@...ulusnetworks.com, jhs@...atatu.com,
        vivien.didelot@...oirfairelinux.com, john.fastabend@...el.com,
        andrew@...n.ch, ivecera@...hat.com
Subject: Re: [patch net-next RFC 0/2] fib4 offload: notifier to let hw to be
 aware of all prefixes

Mon, Sep 19, 2016 at 04:59:22PM CEST, roopa@...ulusnetworks.com wrote:
>On 9/18/16, 11:14 PM, Jiri Pirko wrote:
>> Mon, Sep 19, 2016 at 01:16:17AM CEST, roopa@...ulusnetworks.com wrote:
>>> On 9/18/16, 1:00 PM, Florian Fainelli wrote:
>>>> Le 06/09/2016 à 05:01, Jiri Pirko a écrit :
>>>>> From: Jiri Pirko <jiri@...lanox.com>
>>>>>
>>>>> This is RFC, unfinished. I came across some issues in the process so I would
>>>>> like to share those and restart the fib offload discussion in order to make it
>>>>> really usable.
>>>>>
>>>>> So the goal of this patchset is to allow driver to propagate all prefixes
>>>>> configured in kernel down HW. This is necessary for routing to work
>>>>> as expected. If we don't do that HW might forward prefixes known to kernel
>>>>> incorrectly. Take an example when default route is set in switch HW and there
>>>>> is an IP address set on a management (non-switch) port.
>>>>>
>>>>> Currently, only fibs related to the switch port netdev are offloaded using
>>>>> switchdev ops. This model is not extendable so the first patch introduces
>>>>> a replacement: notifier to propagate fib additions and removals to whoever
>>>>> interested. The second patch makes mlxsw to adopt this new way, registering
>>>>> one notifier block for each mlxsw (asic) instance.
>>>> Instead of introducing another specialization of a notifier_block
>>>> implementation, could we somehow have a kernel-based netlink listener
>>>> which receives the same kind of event information from rtmsg_fib()?
>>>>
>>>> The reason is that having such a facility would hook directly onto
>>>> existing rtmsg_* calls that exist throughout the stack, and that seems
>>>> to scale better.
>>> I was thinking along the same lines. Instead of proliferating notifier blocks
>>> through-out the stack for switchdev offload, putting existing events to use would be nice.
>>>
>>> But the problem though is drivers having to parse the netlink msg again. also, the intent
>>> here is to do the offload first ..before the route is added to the kernel (though i don't see that in
>>> the current series). existing netlink rmsg_fib events are generated after the route is added to the kernel.
>>>
>>>
>>> Jiri, instead of the notifier, do you see a problem with always calling the existing switchdev
>>> offload api for every route  for every asic instance ?. the first device where the route fits wins.
>> There is not list of asic instances. Therefore the notifier fits much better here.
>>
>>
>>
>>> it seems similar to driver registering for notifier and looking at every route ...
>>> am i missing something ?
>>> and the policies you mention could help around selecting the asic instance (FCFS or mirror).
>>> you will need to abstract out the asic instance for switchdev api to call on, but I thought you
>>> already have that in some form in your devlink infrastructure.
>> switchdev asic instances and devlink instances are orthogonal.
>
>maybe it is not today...but the requirement for devlink was to provide a way to communicate
>to the switch driver
>- global switch attributes or
>- things that cannot go via switch ports (exactly the problem you are trying to solve for routes here)

Devlink is a general beast, not switch specific one. I see no need to
use fib->devlink->driver route inside kernel. Devlink is for userspace
facing.


>
>so,  maybe an instance of switch asic modeled via devlink will help here and possibly all/other switchdev
>offload hooks ?

Maybe, but in case of fibs, the notifier just fits great. I see no need
for anything else.