netdev - Re: [RFC 20/20] RDMA/i40iw: Mark i40iw as deprecated

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Date:   Wed, 2 Oct 2019 17:15:45 -0400
From:   Dennis Dalessandro <dennis.dalessandro@...el.com>
To:     Leon Romanovsky <leon@...nel.org>,
        Doug Ledford <dledford@...hat.com>
Cc:     "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "Saleem, Shiraz" <shiraz.saleem@...el.com>,
        "Kirsher, Jeffrey T" <jeffrey.t.kirsher@...el.com>,
        "jgg@...lanox.com" <jgg@...lanox.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>
Subject: Re: [RFC 20/20] RDMA/i40iw: Mark i40iw as deprecated

On 9/28/2019 1:55 AM, Leon Romanovsky wrote:
> On Fri, Sep 27, 2019 at 04:17:15PM -0400, Doug Ledford wrote:
>> On Thu, 2019-09-26 at 21:55 +0200, gregkh@...uxfoundation.org wrote:
>>> On Thu, Sep 26, 2019 at 07:49:44PM +0000, Saleem, Shiraz wrote:
>>>>> Subject: Re: [RFC 20/20] RDMA/i40iw: Mark i40iw as deprecated
>>>>>
>>>>> On Thu, Sep 26, 2019 at 09:45:19AM -0700, Jeff Kirsher wrote:
>>>>>> From: Shiraz Saleem <shiraz.saleem@...el.com>
>>>>>>
>>>>>> Mark i40iw as deprecated/obsolete.
>>>>>>
>>>>>> irdma is the replacement driver that supports X722.
>>>>>
>>>>> Can you simply delete old one and add MODULE_ALIAS() in new
>>>>> driver?
>>>>>
>>>>
>>>> Yes, but we thought typically driver has to be deprecated for a few
>>>> cycles before removing it.
>>>
>>> If you completely replace it with something that works the same, why
>>> keep the old one around at all?
>>>
>>> Unless you don't trust your new code?  :)
>>
>> I have yet to see, in over 20 years of kernel experience, a new driver
>> replace an old driver and not initially be more buggy and troublesome
>> than the old driver.  It takes time and real world usage for the final
>> issues to get sorted out.  During that time, the fallback is often
>> necessary for those real world users.
> 
> How many real users exist in RDMA world who run pure upstream kernel?

I doubt too many especially the latest bleeding edge upstream kernel. 
That could be interesting, but I don't think it's the reality.

Distro kernels could certainly still keep the old driver, and that makes 
a lot of sense.

-Denny