netdev - Re: [PATCH net-next 00/13] Add mlx5 subfunction support

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Date:   Fri, 20 Nov 2020 11:04:58 -0800
From:   "Samudrala, Sridhar" <sridhar.samudrala@...el.com>
To:     Alexander Duyck <alexander.duyck@...il.com>,
        Jakub Kicinski <kuba@...nel.org>
Cc:     David Ahern <dsahern@...il.com>, Jason Gunthorpe <jgg@...dia.com>,
        Parav Pandit <parav@...dia.com>,
        Saeed Mahameed <saeed@...nel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        Jiri Pirko <jiri@...dia.com>,
        "dledford@...hat.com" <dledford@...hat.com>,
        Leon Romanovsky <leonro@...dia.com>,
        "davem@...emloft.net" <davem@...emloft.net>
Subject: Re: [PATCH net-next 00/13] Add mlx5 subfunction support



On 11/20/2020 9:58 AM, Alexander Duyck wrote:
> On Thu, Nov 19, 2020 at 5:29 PM Jakub Kicinski <kuba@...nel.org> wrote:
>>
>> On Wed, 18 Nov 2020 21:35:29 -0700 David Ahern wrote:
>>> On 11/18/20 7:14 PM, Jakub Kicinski wrote:
>>>> On Tue, 17 Nov 2020 14:49:54 -0400 Jason Gunthorpe wrote:
>>>>> On Tue, Nov 17, 2020 at 09:11:20AM -0800, Jakub Kicinski wrote:
>>>>>
>>>>>>> Just to refresh all our memory, we discussed and settled on the flow
>>>>>>> in [2]; RFC [1] followed this discussion.
>>>>>>>
>>>>>>> vdpa tool of [3] can add one or more vdpa device(s) on top of already
>>>>>>> spawned PF, VF, SF device.
>>>>>>
>>>>>> Nack for the networking part of that. It'd basically be VMDq.
>>>>>
>>>>> What are you NAK'ing?
>>>>
>>>> Spawning multiple netdevs from one device by slicing up its queues.
>>>
>>> Why do you object to that? Slicing up h/w resources for virtual what
>>> ever has been common practice for a long time.
>>
>> My memory of the VMDq debate is hazy, let me rope in Alex into this.
>> I believe the argument was that we should offload software constructs,
>> not create HW-specific APIs which depend on HW availability and
>> implementation. So the path we took was offloading macvlan.
> 
> I think it somewhat depends on the type of interface we are talking
> about. What we were wanting to avoid was drivers spawning their own
> unique VMDq netdevs and each having a different way of doing it. The
> approach Intel went with was to use a MACVLAN offload to approach it.
> Although I would imagine many would argue the approach is somewhat
> dated and limiting since you cannot do many offloads on a MACVLAN
> interface.

Yes. We talked about this at netdev 0x14 and the limitations of macvlan 
based offloads.
https://netdevconf.info/0x14/session.html?talk-hardware-acceleration-of-container-networking-interfaces

Subfunction seems to be a good model to expose VMDq VSI or SIOV ADI as a 
netdev for kernel containers. AF_XDP ZC in a container is one of the 
usecase this would address. Today we have to pass the entire PF/VF to a 
container to do AF_XDP.

Looks like the current model is to create a subfunction of a specific 
type on auxiliary bus, do some configuration to assign resources and 
then activate the subfunction.

> 
> With the VDPA case I believe there is a set of predefined virtio
> devices that are being emulated and presented so it isn't as if they
> are creating a totally new interface for this.
> 
> What I would be interested in seeing is if there are any other vendors
> that have reviewed this and sign off on this approach. What we don't
> want to see is Nivida/Mellanox do this one way, then Broadcom or Intel
> come along later and have yet another way of doing this. We need an
> interface and feature set that will work for everyone in terms of how
> this will look going forward.