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@cumulusnetworks.com wrote:

On 9/18/16, 11:14 PM, Jiri Pirko wrote:

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Mon, Sep 19, 2016 at 01:16:17AM CEST, roopa@cumulusnetworks.com wrote:

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On 9/18/16, 1:00 PM, Florian Fainelli wrote:

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Le 06/09/2016 à 05:01, Jiri Pirko a écrit :

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From: Jiri Pirko <redacted>

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.

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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.