Minutes of techboard meeting, 2025-10-01

Minutes of techboard meeting, 2025-10-01

[Bruce Richardson]

TB Members Attending: 7/11
--------------------------
- Bruce
- Thomas
- Kevin
- Konstantin
- Morten
- Jerin
- Maxime

NOTE: The Technical Board meetings take place every second Wednesday at 3 pm UTC
on https://zoom-lfx.platform.linuxfoundation.org/meeting/96459488340?password=d808f1f6-0a28-4165-929e-5a5bcae7efeb
Meetings are public, and DPDK community members are welcome to attend.
Agenda and minutes can be found at http://core.dpdk.org/techboard/minutes
The next meeting will happen on October 15

Agenda
------

* LTS Maintainers,
  - Project is currently short of LTS Maintainers. 
  - Enquiries are ongoing to find additional maintainers. 
  - Volunteers are welcome
  - Mentoring and support from existing maintainers is available for new maintainers

* Use of FAST_FREE and multi-buffer/scattered mbuf flags
  - The flags for enabling fast-free and supporting multi-mbuf packets are
    now documented incompatible
  - Previously they were not defined as incompatible, but that seems to
    have been assumed for some usages.
  - Techboard discussed how best to resolve this incompatibility with
    regards to:
    - ensuring correctness
    - avoiding major churn to DPDK code
    - avoiding churn to end-user code
  - Options discussed:
    1 change definition back to not have the settings incompatible: this
      necessitates checking drivers for correctness
    2 keep as explicitly incompatible and report error if both specified:
      this could break end-user apps, and requires changes to example apps
    3 drop the fast-free flag if multi-segment mbufs are also specified:
      "hides" the issue, but probably minimises changes. Would need to
      decide whether the dropping of flag done in drivers vs ethdev level.
      Pros and cons to both options. Needs clear documenting.
  - No firm decision reached, will discuss more over email.

Recurring item list Discussion
------------------------------

TB reviewed our standard list of recurring items for updates.

* Examples to remove:
  - it was noted that work is being done on DCB functionality, and
    separating it from VMDQ.
  - follow up with patch author (as presumed knowledgable in this area) as
    to whether we need to keep both vmdq and vmdq+dcb sample apps.

* Doc Maintenance:
  - Project had employed a technical writer to help cleanup docs, but this
    contract has now finished
  - Most output patches from the contract have been merged but there is at
    least one set that needs futher update
  - Discussed use of AI for documentation updates
    - for mechanical updates AI may be of help
    - skepticism of usefulness beyond that

* Community Lab:
  - Patrick provided a short update on lab work:
    - DTS Development ongoing
    - Team at UNH has produced some new introductory videos on setting up
      and using DTS.
  - Process has just started on planning for lab priorities for 2026, in
    order to have that in place for end-of-year.

RE: Minutes of techboard meeting, 2025-10-01

[Morten Brørup]

> From: Bruce Richardson [mailto:bruce.richardson@intel.com]
> Sent: Friday, 3 October 2025 11.18
> Subject: Minutes of techboard meeting, 2025-10-01

> * Use of FAST_FREE and multi-buffer/scattered mbuf flags
>   - The flags for enabling fast-free and supporting multi-mbuf packets
> are
>     now documented incompatible
>   - Previously they were not defined as incompatible, but that seems to
>     have been assumed for some usages.
>   - Techboard discussed how best to resolve this incompatibility with
>     regards to:
>     - ensuring correctness
>     - avoiding major churn to DPDK code
>     - avoiding churn to end-user code
>   - Options discussed:
>     1 change definition back to not have the settings incompatible:
> this
>       necessitates checking drivers for correctness
>     2 keep as explicitly incompatible and report error if both
> specified:
>       this could break end-user apps, and requires changes to example
> apps
>     3 drop the fast-free flag if multi-segment mbufs are also
> specified:
>       "hides" the issue, but probably minimises changes. Would need to
>       decide whether the dropping of flag done in drivers vs ethdev
> level.
>       Pros and cons to both options. Needs clear documenting.
>   - No firm decision reached, will discuss more over email.

IMO, the patch [1] making MBUF_FAST_FREE and MULTI_SEGS explicitly incompatible should be reverted, at least for RC1.
That will take the project back to the state it was in before we started this discussion.
And all the examples broken by the patch (because they use both TX offloads) will not need fixing.

[1]: https://patchwork.dpdk.org/project/dpdk/patch/20250803194218.683318-3-mb@smartsharesystems.com/

Use of TX offload flags MBUF_FAST_FREE and MULTI_SEGS

[Morten Brørup]

> From: Bruce Richardson [mailto:bruce.richardson@intel.com]
> Sent: Friday, 3 October 2025 11.18
> Subject: Minutes of techboard meeting, 2025-10-01

> * Use of FAST_FREE and multi-buffer/scattered mbuf flags
>   - The flags for enabling fast-free and supporting multi-mbuf packets
> are
>     now documented incompatible
>   - Previously they were not defined as incompatible, but that seems to
>     have been assumed for some usages.
>   - Techboard discussed how best to resolve this incompatibility with
>     regards to:
>     - ensuring correctness
>     - avoiding major churn to DPDK code
>     - avoiding churn to end-user code
>   - Options discussed:
>     1 change definition back to not have the settings incompatible:
> this
>       necessitates checking drivers for correctness
>     2 keep as explicitly incompatible and report error if both
> specified:
>       this could break end-user apps, and requires changes to example
> apps
>     3 drop the fast-free flag if multi-segment mbufs are also
> specified:
>       "hides" the issue, but probably minimises changes. Would need to
>       decide whether the dropping of flag done in drivers vs ethdev
> level.
>       Pros and cons to both options. Needs clear documenting.
>   - No firm decision reached, will discuss more over email.

IMO, the patch [1] making MBUF_FAST_FREE and MULTI_SEGS explicitly incompatible should be reverted, at least for RC1.
That will take the project back to the state it was in before we started this discussion.
And all the examples broken by the patch (because they use both TX offloads) will not need fixing.

[1]: https://patchwork.dpdk.org/project/dpdk/patch/20250803194218.683318-3-mb@smartsharesystems.com/

Re: Use of TX offload flags MBUF_FAST_FREE and MULTI_SEGS

[Ivan Malov]

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Hi Morten,

I apologise for my original notice about the co-existence of these flags.
Were it not for my notice, things wouldn't have gone wrong, I take it.

Thank you.

On Mon, 6 Oct 2025, Morten Brørup wrote:

>> From: Bruce Richardson [mailto:bruce.richardson@intel.com]
>> Sent: Friday, 3 October 2025 11.18
>> Subject: Minutes of techboard meeting, 2025-10-01
>
>> * Use of FAST_FREE and multi-buffer/scattered mbuf flags
>>   - The flags for enabling fast-free and supporting multi-mbuf packets
>> are
>>     now documented incompatible
>>   - Previously they were not defined as incompatible, but that seems to
>>     have been assumed for some usages.
>>   - Techboard discussed how best to resolve this incompatibility with
>>     regards to:
>>     - ensuring correctness
>>     - avoiding major churn to DPDK code
>>     - avoiding churn to end-user code
>>   - Options discussed:
>>     1 change definition back to not have the settings incompatible:
>> this
>>       necessitates checking drivers for correctness
>>     2 keep as explicitly incompatible and report error if both
>> specified:
>>       this could break end-user apps, and requires changes to example
>> apps
>>     3 drop the fast-free flag if multi-segment mbufs are also
>> specified:
>>       "hides" the issue, but probably minimises changes. Would need to
>>       decide whether the dropping of flag done in drivers vs ethdev
>> level.
>>       Pros and cons to both options. Needs clear documenting.
>>   - No firm decision reached, will discuss more over email.
>
> IMO, the patch [1] making MBUF_FAST_FREE and MULTI_SEGS explicitly incompatible should be reverted, at least for RC1.
> That will take the project back to the state it was in before we started this discussion.
> And all the examples broken by the patch (because they use both TX offloads) will not need fixing.
>
> [1]: https://patchwork.dpdk.org/project/dpdk/patch/20250803194218.683318-3-mb@smartsharesystems.com/
>
>

Re: Minutes of techboard meeting, 2025-10-01

[Stephen Hemminger]

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To help with definition of fast free flag, I would like the documentation
to be better.

Something like:
Fast free flag allows driver to avoid expensive atomic operators on ref
count and assume all mbufs in a burst are from the same pool.

Should also add debug asserts in drivers implenting fast free.

On Mon, Oct 6, 2025, 16:40 Morten Brørup <mb@smartsharesystems.com> wrote:

> > From: Bruce Richardson [mailto:bruce.richardson@intel.com]
> > Sent: Friday, 3 October 2025 11.18
> > Subject: Minutes of techboard meeting, 2025-10-01
>
> > * Use of FAST_FREE and multi-buffer/scattered mbuf flags
> >   - The flags for enabling fast-free and supporting multi-mbuf packets
> > are
> >     now documented incompatible
> >   - Previously they were not defined as incompatible, but that seems to
> >     have been assumed for some usages.
> >   - Techboard discussed how best to resolve this incompatibility with
> >     regards to:
> >     - ensuring correctness
> >     - avoiding major churn to DPDK code
> >     - avoiding churn to end-user code
> >   - Options discussed:
> >     1 change definition back to not have the settings incompatible:
> > this
> >       necessitates checking drivers for correctness
> >     2 keep as explicitly incompatible and report error if both
> > specified:
> >       this could break end-user apps, and requires changes to example
> > apps
> >     3 drop the fast-free flag if multi-segment mbufs are also
> > specified:
> >       "hides" the issue, but probably minimises changes. Would need to
> >       decide whether the dropping of flag done in drivers vs ethdev
> > level.
> >       Pros and cons to both options. Needs clear documenting.
> >   - No firm decision reached, will discuss more over email.
>
> IMO, the patch [1] making MBUF_FAST_FREE and MULTI_SEGS explicitly
> incompatible should be reverted, at least for RC1.
> That will take the project back to the state it was in before we started
> this discussion.
> And all the examples broken by the patch (because they use both TX
> offloads) will not need fixing.
>
> [1]:
> https://patchwork.dpdk.org/project/dpdk/patch/20250803194218.683318-3-mb@smartsharesystems.com/
>
>

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