[RFC PATCH] net/dpaa2: fix RSS at inner level for non-tunnelled traffic

[Hemant Agrawal]

On 15-07-2026 22:30, Maxime Leroy wrote:
> Hi Hemant,
>
> Do you have any preference between the different approaches proposed below?
>
> Regards,
>
> Maxime Leroy
>
> On Tue, Jun 30, 2026 at 2:39 PM Maxime Leroy<maxime at leroys.fr> wrote:
>> When RTE_ETH_RSS_LEVEL_INNERMOST is requested, the IP key extracts use
>> the innermost header index (HDR_INDEX_LAST). The hardware only resolves
>> that index when several IP headers are stacked: for a non-tunnelled
>> frame, which carries a single IP header, the extraction returns nothing.
>> The RSS hash is then constant and all such frames are steered to a
>> single Rx queue.
>>
>> Always also extract the outer IP (header index 0), which the hardware
>> resolves for any frame. Non-tunnelled frames are thus hashed on their
>> only IP header, while tunnelled frames keep being hashed on their inner
>> IP.
>>
>> This is a deliberate tradeoff: the ethdev API defines
>> RTE_ETH_RSS_LEVEL_INNERMOST as hashing the innermost header only, but the
>> hardware cannot do that without breaking RSS for plain traffic. As a
>> consequence, two tunnelled flows with the same inner header but
>> different outer IPs may hash to different queues. This limitation is
>> documented in the dpaa2 guide.
>>
>> Alternatives considered (feedback welcome, hence RFC):
>>
>> - Hash both outer and inner only under RTE_ETH_RSS_LEVEL_PMD_DEFAULT and
>>    keep INNERMOST strictly inner-only. The ethdev API leaves the default
>>    level to the PMD, so this stays API-compliant; it changes the default
>>    hash for tunnelled traffic.
>>
>> - Add a generic RTE_ETH_RSS_LEVEL_OUTER_INNER value to the ethdev API so
>>    applications can request hashing on both encapsulation levels
>>    explicitly, instead of overloading INNERMOST. This needs an ethdev API
>>    change and agreement from other PMDs.
>>
>> Fixes: 32f701671d2f ("net/dpaa2: support inner RSS level for tunnelled traffic")
>> Signed-off-by: Maxime Leroy<maxime at leroys.fr>

Hi Maxime,

My preference is to keep |RTE_ETH_RSS_LEVEL_INNERMOST| semantics 
unchanged and strictly hash on the innermost header.

I would rather use the PMD-defined default level to provide the best RSS 
distribution for both plain and tunnelled traffic. Overloading 
|INNERMOST| to include the outer IP makes the behavior diverge from the 
ethdev definition and may surprise applications relying on true 
inner-header affinity.

Longer term, an explicit |OUTER_INNER| RSS level would be the cleanest 
solution if there is interest from other PMDs.

Regards,

Hemant
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