Re: [PATCH v4 2/2] virtio_net: Extend virtio to use VF datapath when available

[Jiri Pirko <jiri@resnulli.us>]

Tue, Mar 06, 2018 at 08:08:21PM CET, alexander.duyck@gmail.com wrote:
>On Mon, Mar 5, 2018 at 7:15 PM, Stephen Hemminger
><stephen@networkplumber.org> wrote:
>> On Mon, 5 Mar 2018 14:47:20 -0800
>> Alexander Duyck <alexander.duyck@gmail.com> wrote:
>>
>>> On Mon, Mar 5, 2018 at 2:30 PM, Jiri Pirko <jiri@resnulli.us> wrote:
>>> > Mon, Mar 05, 2018 at 05:11:32PM CET, stephen@networkplumber.org wrote:
>>> >>On Mon, 5 Mar 2018 10:21:18 +0100
>>> >>Jiri Pirko <jiri@resnulli.us> wrote:
>>> >>
>>> >>> Sun, Mar 04, 2018 at 10:58:34PM CET, alexander.duyck@gmail.com wrote:
>>> >>> >On Sun, Mar 4, 2018 at 10:50 AM, Jiri Pirko <jiri@resnulli.us> wrote:
>>> >>> >> Sun, Mar 04, 2018 at 07:24:12PM CET, alexander.duyck@gmail.com wrote:
>>> >>> >>>On Sat, Mar 3, 2018 at 11:13 PM, Jiri Pirko <jiri@resnulli.us> wrote:
>>> >>>
>>> >>> [...]
>>> >>>
>>> >>> >
>>> >>> >>>Currently we only have agreement from Michael on taking this code, as
>>> >>> >>>such we are working with virtio only for now. When the time comes that
>>> >>> >>
>>> >>> >> If you do duplication of netvsc in-driver bonding in virtio_net, it will
>>> >>> >> stay there forever. So what you say is: "We will do it halfway now
>>> >>> >> and promise to fix it later". That later will never happen, I'm pretty
>>> >>> >> sure. That is why I push for in-driver bonding shared code as a part of
>>> >>> >> this patchset.
>>> >>> >
>>> >>> >You want this new approach and a copy of netvsc moved into either core
>>> >>> >or some module of its own. I say pick an architecture. We are looking
>>> >>> >at either 2 netdevs or 3. We are not going to support both because
>>> >>> >that will ultimately lead to a terrible user experience and make
>>> >>> >things quite confusing.
>>> >>> >
>>> >>> >> + if you would be pushing first driver to do this, I would understand.
>>> >>> >> But the first driver is already in. You are pushing second. This is the
>>> >>> >> time to do the sharing, unification of behaviour. Next time is too late.
>>> >>> >
>>> >>> >That is great, if we want to share then lets share. But what you are
>>> >>> >essentially telling us is that we need to fork this solution and
>>> >>> >maintain two code paths, one for 2 netdevs, and another for 3. At that
>>> >>> >point what is the point in merging them together?
>>> >>>
>>> >>> Of course, I vote for the same behaviour for netvsc and virtio_net. That
>>> >>> is my point from the very beginning.
>>> >>>
>>> >>> Stephen, what do you think? Could we please make virtio_net and netvsc
>>> >>> behave the same and to use a single code with well-defined checks and
>>> >>> restrictions for this feature?
>>> >>
>>> >>Eventually, yes both could share common code routines. In reality,
>>> >>the failover stuff is only a very small part of either driver so
>>> >>it is not worth stretching to try and cover too much. If you look,
>>> >>the failover code is just using routines that already exist for
>>> >>use by bonding, teaming, etc.
>>> >
>>> > Yeah, we consern was also about the code that processes the netdev
>>> > notifications and does auto-enslave and all related stuff.
>>>
>>> The concern was the driver model. If we expose 3 netdevs or 2 with the
>>> VF driver present. Somehow this is turning into a "merge netvsc into
>>> virtio" think and that isn't the subject that was being asked.
>>>
>>> Ideally we want one model for this. Either 3 netdevs or 2. The problem
>>> is 2 causes issues in terms of performance and will limit features of
>>> virtio, but 2 is the precedent set by netvsc. We need to figure out
>>> the path forward for this. There is talk about "sharing" but it is
>>> hard to make these two approaches share code when they are doing two
>>> very different setups and end up presenting themselves as two very
>>> different driver models.
>>
>> I appreciate this discussion, and it has helped a lot.
>>
>> Netvsc is stuck with 2 netdev model for the foreseeable future.
>> We already failed once with the bonding model, and that created a lot of
>> pain. The current model is working well and have convinced the major distros
>> to support the two netdev model and don't want to back.
>>
>> Very open to optimizations and ways to smooth out the rough edges.
>
>Thank you for clarifying this Stephen.
>
>Okay. So with things defined such that we are doing a 2 netdev model
>for netvsc, and a 3 netdev model for virtio, is it still in our
>interest for us to try making a shared library between the two? In my
>mind, the virtnet_bypass becomes the way we go forward for any future
>solutions. I say we treat the netvsc approach as a "legacy" approach
>and avoid creating any new libraries or drivers to support it, and
>instead just focus on the 3 netdev approach as the way this is to be
>done going forward. That way we avoid anyone else trying to implement
>something like the 2 netdev solution in the future.
>
>So getting back to the code here. Should we split the virtnet_bypass
>code out into a separate module? My preference would be to let this
>incubate as a part of virtio_net until either there is another user,
>or it becomes big enough that it needs to be moved. That said, there

What do you mean by "big enough"? I hope that is will never be extended
by anything. If you need to do anything more complex, you should use
bong/team.

I definitelly vote for a separate common shared code for both netvsc and
virtio_net - even if you use 2 and 3 netdev model, you could share the
common code. Strict checks and limitation should be in place.