Re: SRIOV switchdev mode BoF minutes

[Or Gerlitz <gerlitz.or@gmail.com>]

On Sun, Nov 12, 2017 at 10:38 PM, Alexander Duyck
<alexander.duyck@gmail.com> wrote:
> On Sun, Nov 12, 2017 at 11:49 AM, Or Gerlitz <gerlitz.or@gmail.com> wrote:
>> Hi Dave and all,
>>
>> During and after the BoF on SRIOV switchdev mode, we came into a
>> consensus among the developers from four different HW vendors (CC
>> audience) that a correct thing to do would be to disallow any new
>> extensions to the legacy mode.
>>
>> The idea is to put focus on the new mode and not add new UAPIs and
>> kernel code which was turned to be a wrong design which does not allow
>> for properly offloading a kernel switching SW model to e-switch HW.

> You may not recall but we tried to transition the i40e driver over to
> SwitchDev, the parts supported by i40e have a much more robust l2
> forwarding framework than the 82599, and the result was we were told
> that while we might look at doing port representors some other way,
> there was no way we could use switchdev since the hardware couldn't
> support the requirements of switchdev in terms of default routes and
> forwarding behavior. I am planning to resolve the port representor
> issue by looking at coming up with something like a "source mode"
> macvlan based port representor. I figure that is probably the closest
> match for what the Intel hardware does since really the VFs are
> nothing more than a physical macvlan interface in and of themselves as
> the hardware doesn't have a full switch.

Hi Alex,

The what we call slow path requirements are the following:

1. xmit on VF rep always turns to a receive on the VF, regardless of
the offloaded
SW steering rules ("send-to-vport")

2. xmit on VF which doesn't meet any offloaded SW steering rules must
be recieved
into the host OS from the VF rep

1,2 above must hold also for the uplink and the PF reps

When the i40e limitation was described to @ netdev, it seems you have a problem
with VF xmit that should be turned to be a recv on the VF rep but also
goes to the wire.

It smells as if a FW patch can solve that, isn't that?

> I would have to disagree with this. For devices such as 82599 that
> doesn't have a true switch this may limit future functionality since
> we can't move it over to switchdev mode. For example one thing I may
> need to add is the ability to disable multicast and broadcast receive
> on a per-VF basis at some point in the future.

We are on the same boat with ConnectX3/mlx4, so us lucky that misery loves
company (my google search also yielded "many narrow-half consolation" is that
completely unrelated?) - the legacy mode for ixgbe/mlx4 is there for ~8-10 years
- and since then both companies had 2-3 newer HW generations. I don't see why
you can't come to your customers and tell that newish functionality needs newer
HW - it will also help sell more from the new stuff..  If you keep
extending the legacy
mode, more ppl/drivers will do that as well and it will not let us go
in the right direction.

Or.