Use of TX offload flags MBUF_FAST_FREE and MULTI_SEGS

[Ivan Malov]

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 at 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/
>
>