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

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Message-ID: <57DF2041.3040509@cumulusnetworks.com>
Date:   Sun, 18 Sep 2016 16:16:17 -0700
From:   Roopa Prabhu <roopa@...ulusnetworks.com>
To:     Florian Fainelli <f.fainelli@...il.com>
CC:     Jiri Pirko <jiri@...nulli.us>, 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

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.
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.