Message-ID: <49d7e1ba-0d07-43d2-a5e7-81f142152f8a@gmail.com>
Date: Tue, 9 Apr 2024 06:05:47 -0700
From: Florian Fainelli <f.fainelli@...il.com>
To: Jiri Pirko <jiri@...nulli.us>
Cc: Alexander Duyck <alexander.duyck@...il.com>,
 Jason Gunthorpe <jgg@...dia.com>, Paolo Abeni <pabeni@...hat.com>,
 Jakub Kicinski <kuba@...nel.org>, John Fastabend <john.fastabend@...il.com>,
 netdev@...r.kernel.org, bhelgaas@...gle.com, linux-pci@...r.kernel.org,
 Alexander Duyck <alexanderduyck@...com>, davem@...emloft.net,
 Christoph Hellwig <hch@....de>
Subject: Re: [net-next PATCH 00/15] eth: fbnic: Add network driver for Meta
 Platforms Host Network Interface



On 4/9/2024 3:56 AM, Jiri Pirko wrote:
> Mon, Apr 08, 2024 at 11:36:42PM CEST, f.fainelli@...il.com wrote:
>> On 4/8/24 09:51, Jiri Pirko wrote:
>>> Mon, Apr 08, 2024 at 05:46:35PM CEST, alexander.duyck@...il.com wrote:
>>>> On Mon, Apr 8, 2024 at 4:51 AM Jiri Pirko <jiri@...nulli.us> wrote:
>>>>>
>>>>> Fri, Apr 05, 2024 at 08:38:25PM CEST, alexander.duyck@...il.com wrote:
>>>>>> On Fri, Apr 5, 2024 at 8:17 AM Jason Gunthorpe <jgg@...dia.com> wrote:
>>>>>>>
>>>>>>> On Fri, Apr 05, 2024 at 07:24:32AM -0700, Alexander Duyck wrote:
>>>>>>>>> Alex already indicated new features are coming, changes to the core
>>>>>>>>> code will be proposed. How should those be evaluated? Hypothetically
>>>>>>>>> should fbnic be allowed to be the first implementation of something
>>>>>>>>> invasive like Mina's DMABUF work? Google published an open userspace
>>>>>>>>> for NCCL that people can (in theory at least) actually run. Meta would
>>>>>>>>> not be able to do that. I would say that clearly crosses the line and
>>>>>>>>> should not be accepted.
>>>>>>>>
>>>>>>>> Why not? Just because we are not commercially selling it doesn't mean
>>>>>>>> we couldn't look at other solutions such as QEMU. If we were to
>>>>>>>> provide a github repo with an emulation of the NIC would that be
>>>>>>>> enough to satisfy the "commercial" requirement?
>>>>>>>
>>>>>>> My test is not "commercial", it is enabling open source ecosystem vs
>>>>>>> benefiting only proprietary software.
>>>>>>
>>>>>> Sorry, that was where this started where Jiri was stating that we had
>>>>>> to be selling this.
>>>>>
>>>>> For the record, I never wrote that. Not sure why you repeat this over
>>>>> this thread.
>>>>
>>>> Because you seem to be implying that the Meta NIC driver shouldn't be
>>>> included simply since it isn't going to be available outside of Meta.
>>>> The fact is Meta employs a number of kernel developers and as a result
>>>> of that there will be a number of kernel developers that will have
>>>> access to this NIC and likely do development on systems containing it.
>>>> In addition simply due to the size of the datacenters that we will be
>>>> populating there is actually a strong likelihood that there will be
>>>> more instances of this NIC running on Linux than there are of some
>>>> other vendor devices that have been allowed to have drivers in the
>>>> kernel.
>>>
>>> So? The gain for community is still 0. No matter how many instances is
>>> private hw you privately have. Just have a private driver.
>>
>> I am amazed and not in a good way at how far this has gone, truly.
>>
>> This really is akin to saying that any non-zero driver count to maintain is a
>> burden on the community. Which is true, by definition, but if the goal was to
>> build something for no users, then clearly this is the wrong place to be in,
>> or too late. The systems with no users are the best to maintain, that is for
>> sure.
>>
>> If the practical concern is wen you make tree wide API change that fbnic
>> happens to use, and you have yet another driver (fbnic) to convert, so what?
>> Work with Alex ahead of time, get his driver to be modified, post the patch
>> series. Even if Alex happens to move on and stop being responsible and there
>> is no maintainer, so what? Give the driver a depreciation window for someone
>> to step in, rip it, end of story. Nothing new, so what has specifically
>> changed as of April 4th 2024 to oppose such strong rejection?
> 
> How you describe the flow of internal API change is totally distant from
> reality. Really, like no part is correct:
> 1) API change is responsibility of the person doing it. Imagine working
>     with 40 driver maintainers for every API change. I did my share of
>     API changes in the past, maintainer were only involved to be cced.

As a submitter you propose changes and silence is acknowledgement. If 
one of your API changes broke someone's driver and they did not notify 
you of the breakage during the review cycle, it falls on their shoulder 
to fix it for themselves and they should not be holding back your work, 
that would not be fair. If you know about the breakage, and there is 
still no fix, that is an indication the driver is not actively used and 
maintained.

This also does not mean you have to do the entire API changes to a 
driver you do not know about on your own. Nothing ever prevents you from 
posting the patches as RFC and say: "here is how I would go about 
changing your driver, please review and help me make corrections". If 
the driver maintainers do not respond there is no reason their lack of 
involvement should refrain your work, and so your proposed changes will 
be merged eventually.

Is not this the whole point of being a community and be able to delegate 
and mitigate the risk of large scale changes?

> 2) To deprecate driver because the maintainer is not responsible. Can
>     you please show me one example when that happened in the past?

I cannot show you an example because we never had to go that far and I 
did not say that this is an established practice, but that we *could* do 
that if we ever reached that point.

> 
> 
>>
>> Like it was said, there are tons of drivers in the Linux kernel that have a
>> single user, this one might have a few more than a single one, that should be
>> good enough.
> 
> This will have exactly 0. That is my point. Why to merge something
> nobody will ever use?

Even if Alex and his firmware colleague end up being the only two people 
using this driver if the decision is to make it upstream because this is 
the desired distribution and development model of the driver we should 
respect that.

And just to be clear, we should not be respecting that because Meta, or 
Alex or anyone decided that they were doing the world a favor by working 
in the open rather than being closed door, but simply because we cannot 
*presume* about their intentions and the future.

For drivers specifically, yes, there is a question of to which degree 
can we scale horizontally, and I do not think there is ever going to be 
an answer to that, as we will continue to see new drivers emerge, 
possibly with few users, for some definition of few.
-- 
Florian

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