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

[Jason Wang <jasowang@redhat.com>]

On 2020/11/24 下午3:01, Jason Wang wrote:
>
> On 2020/11/21 上午3:04, Samudrala, Sridhar wrote:
>>
>>
>> On 11/20/2020 9:58 AM, Alexander Duyck wrote:
>>> On Thu, Nov 19, 2020 at 5:29 PM Jakub Kicinski <kuba@kernel.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.
>
>
> vDPA doesn't have any limitation of how the devices is created or 
> implemented. It could be predefined or created dynamically. vDPA 
> leaves all of those to the parent device with the help of a unified 
> management API[1]. E.g It could be a PCI device (PF or VF), 
> sub-function or  software emulated devices.


Miss the link, https://www.spinics.net/lists/netdev/msg699374.html.

Thanks


>
>
>>>
>>> What I would be interested in seeing is if there are any other vendors
>>> that have reviewed this and sign off on this approach.
>
>
> For "this approach" do you mean vDPA subfucntion? My understanding is 
> that it's totally vendor specific, vDPA subsystem don't want to be 
> limited by a specific type of device.
>
>
>>> 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.
>
> For feature set,  it would be hard to force (we can have a 
> recommendation set of features) vendors to implement a common set of 
> features consider they can be negotiated. So the management interface 
> is expected to implement features like cpu clusters in order to make 
> sure the migration compatibility, or qemu can assist for the missing 
> feature with performance lose.
>
> Thanks
>
>