Re: [dpdk-dev] [RFC] Proposals and notes from ABI stability panel @ DPDK Userspace

[Kevin Traynor <ktraynor@redhat.com>]

On 23/09/2019 18:51, Ray Kinsella wrote:
> Folks,
> 
> As you may be aware, there was a panel on ABI Stability @ DPDK
> Userspace.  There where a number of proposed amendments to the ABI
> stability proposal made, as well as a number of points and comments, you
> will find all these below. The proposals needs further discussion so
> please chime in below.
> 
> Thanks to Tim for capturing while I was busy on the stage.
> 

Thanks for the notes Tim,

> Thanks,
> 
> Ray K
> 
> 
> Table of Contents
> _________________
> 
> 1. Proposals from the panel discussion.
> .. 1. Developer releases (versus User Releases)
> .. 2. Core and non-core packaging
> .. 3. Approach for public data structures
> .. 4. Delaying v19.11
> 2. Other notes from the panel discussion.
> .. 1. Performance as the paramount goal.
> .. 2. Length of ABI Stability.
> .. 3. Testing ABI Stability
> .. 4. Call to action
> 
> 
> 1 Proposals from the panel discussion.
> ======================================
> 
> 1.1 Developer releases (versus User Releases)
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
>   - Summary: Differentiate between "developer" and "user" releases.
>     - 1 year is too long to wait to upstream a new feature which breaks
>       ABI.
>     - Developer releases would be for use by the development community
>       only.
>     - A proposed compromise was that the .08 release would be the only
>       "developer release".
> 
> 
> 1.2 Core and non-core packaging
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
>   - Summary: OS packaging doesn't include all libraries.
>     - This would create a delta between the community ABI, and the OS
>       packaging.
>     - OS packagers rational is that some libraries are used very rarely.
> 
> 
> 1.3 Approach for public data structures
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
>   - Summary: Public/exposed data structures are tricky for ABI
>     stability.
>     - See discussion @
> 
> <http://inbox.dpdk.org/dev/980083c6-130a-9658-f82b-0c9ddc7cc0cc@ashroe.eu/>
> 
> 
> 1.4 Delaying v19.11
> ~~~~~~~~~~~~~~~~~~~
> 
>   - Summary: push v19.11 to v19.12 to make more time to prepare and wave
>     the depreciation process.
>     - OVS take Nov LTS release in their Feb release. Delaying 19.11 may
>       have an impact on this.

To give some more info about OVS. tldr there is a soft freeze on Jan 1st
but an update that is being discussed/reviewed could go in until Jan
15th when the OVS 2.13 branch would be created.

Thomas is indeed right in that there is a development branch in OVS that
is intended to keep up with DPDK master with a view to finding any
integration issues early.

More info here
http://docs.openvswitch.org/en/latest/internals/release-process/#release-strategy

>     - Not easy to change release at this stage as many things depend on
>       it (OS distros etc.).
> 

In the short term, based on the feedback at the conference and to give
something concrete to be considered, here is a suggestion,

ABI freeze starts at 20.02 for 9 months, with a review as planned to see
if 20.11 should be frozen 2 years.

pros:
+ Eliminates any need for delaying 19.11 release

+ Allows maintainers to stick to current deprecation policy if they need
to make changes prior to freeze (Based on comment from Hemmant)

+ Not sure if it's worthy of a new bullet or clear from above but I
would add that changing the release cycle/deprecation policy etc 2 weeks
(I think) before RC1 is late to say the least and there is no notice to
users

+ Means that any changes required prior to freeze are not rushed with
usual big LTS release (19.11). Gives more time and maybe during a saner
release cycle (20.02)

cons:
- With view for possible 20.11 freeze, gives 2 releases to tease out
process instead of 3

- Perhaps it is desirable for some users to have the 19.11 LTS ABI
compatible with 20.02/05/08 releases

I've tried to keep them objective, of course people will have different
opinions about starting a freeze now vs. later etc. too.

thanks,
Kevin.

> 
> 2 Other notes from the panel discussion.
> ========================================
> 
> 2.1 Performance as the paramount goal.
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
>   - Some users, would trade performance for better readability and
>     debug-ability.
>   - Skepticism that micro-benchmarks reflect real world performance.
> 
> 
> 2.2 Length of ABI Stability.
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
>   - Some users, questioned if 1 year would be long enough.
>   - It was clarified that the 1 year period, would be reviewed after the
>     first year with the intention of lengthening the period.
> 
> 
> 2.3 Testing ABI Stability
> ~~~~~~~~~~~~~~~~~~~~~~~~~
> 
>   - More work for developers and validation teams. Need to validate
>     multiple paths for symbol versioning.
> 
> 
> 2.4 Call to action
> ~~~~~~~~~~~~~~~~~~
> 
>   - We should do something. So we don’t want to have the same
>     conversation again in a year.
>