Re: [dpdk-stable] [PATCH 20.11 v2 00/18] Backport the new VLAN design for Intel ice PMD

[Kevin Traynor <ktraynor@redhat.com>]

On 21/06/2021 09:34, Wang, Haiyue wrote:
>> -----Original Message-----
>> From: Thomas Monjalon <thomas@monjalon.net>
>> Sent: Monday, June 21, 2021 16:29
>> To: Kevin Traynor <ktraynor@redhat.com>; Xueming(Steven) Li <xuemingl@nvidia.com>; Luca Boccassi
>> <bluca@debian.org>; Wang, Haiyue <haiyue.wang@intel.com>; christian.ehrhardt@canonical.com
>> Cc: stable@dpdk.org; Zhang, Qi Z <qi.z.zhang@intel.com>; Fu, Qi <qi.fu@intel.com>; techboard@dpdk.org
>> Subject: Re: [dpdk-stable] [PATCH 20.11 v2 00/18] Backport the new VLAN design for Intel ice PMD
>>
>> 18/06/2021 05:22, Wang, Haiyue:
>>> From: Kevin Traynor <ktraynor@redhat.com>
>>>> On 17/06/2021 09:53, Xueming(Steven) Li wrote:
>>>>> From: Wang, Haiyue <haiyue.wang@intel.com>
>>>>>> From: Luca Boccassi <bluca@debian.org>
>>>>>>> On Fri, 2021-06-11 at 15:15 +0800, Haiyue Wang wrote:
>>>>>>>> When LTS 20.11 was released, the Intel ice PMD has a basic VLAN
>>>>>>>> offload, which can only handle single VLAN mode for firmware
>>>>>>>> limitation. Now the firmware is updated to support double VLAN mode
>>>>>>>> and single VLAN mode at the same time.
>>>>>>>> It depends on the driver to do selection at the boot time.
>>>>>>>>
>>>>>>>> As VLAN protocol handling like strip, filter, flow is very common
>>>>>>>> use, we request to support the ice PMD can run on the latest
>>>>>>>> firmware for enabling the new design. This is compatible backport as the main tree.
>> [...]
>>>>>>>>  19 files changed, 1545 insertions(+), 363 deletions(-)  create mode
>> [...]
>>>>>>> At 1.9k diffstat, this series is quite large. Given it's a new
>>>>>>> feature, rather than a series of bug fixes, this would seem a bit risky to me.
>>>>>>> Final word of course belongs to Xueming, since he's managing this one.
>>
>> [...]
>>>>>> 06. Is it obvious that the feature will not impact existing functionality?
>>>>>>
>>>>>> Yes.
>>>>
>>>> No. It is 1.9KLOC change. The key part of the question is "obvious". It
>>>> was meant so the maintainer could use their judgement and review that
>>>> for example, a few lines of code adding a PCI ID or adding a case in a
>>>> switch statement, is obviously not going to impact existing functionality.
>>>> On the other hand, for a more complex code change to existing code, it
>>>> is not immediately obvious that there would be no risk to existing
>>>> functionality.
>>
>> [...]
>>>>>> 11. Is there a community consensus about the backport?
>>>>>>
>>>>>> ...
>>>>>
>>>>> Kevin happens to updated the documents on new feature backport 4 months ago, thanks for checking
>>>> them
>>>>> one by one. Luca's only concern is size of the series, driver vendor is on it's own risk to
>> backport
>>>> a big patch set.
>>>>> The series supports new fw and QinQ, is it easy to split?
>>>>>
>>>>> Kevin, is this the first case of feature backport? How do you think?
>>>>>
>>>>
>>>> Like Luca, main concern would be the size and intrusiveness of the
>>>> changes, and if it's ok to change 1.9KLOC in this driver now, then why
>>>> not 20KLOC in next release to multiple drivers. I had pushed against a
>>>
>>> TBH, we won't want to change the stable i40e, ixgbe PMDs, but ice is a fresh
>>> one, current VLAN has a limited usage, customer is hard to use. That's why we
>>> try to request to backport the new VLAN design.
>>
>> Yes ice is quite recent.
>> If a required feature is not working, it should motivate to upgrade.
>> Because ice is "fresh", I don't understand why sticking to 20.11.
>> My concern is that backporting this big feature would create a precedent,
>> so all users will require to stick on the last LTS when getting
>> all the new reworked features.
> 
> "Performance improvements are generally not considered to be fixes, but may be
>  considered in some cases where:
> 
> It is fixing a performance regression that occurred previously.
> An existing feature in LTS is not usable as intended without it."
> 
> I think "An existing feature in LTS is not usable as intended without it " can
> be one reason, since the old design is out of date in two year of LTS lifetime.
> 

This section is about performance improvements e.g. optimising some code
to increase throughput. Added because it's not as obvious whether
performance improvements are a fix or new functionality and it was
discussed a few times. I don't believe it is relevant to these patches.

>> I think it would be a bad situation for all of us.
>>
>>
>