[RFC v6 0/6] Lcore variables

[Mattias Rönnblom]

On 2024-09-02 16:42, Morten Brørup wrote:
>> From: Mattias Rönnblom [mailto:mattias.ronnblom at ericsson.com]
>> Sent: Monday, 6 May 2024 10.27
>>
>> This RFC presents a new API <rte_lcore_var.h> for static per-lcore id
>> data allocation.
>>
>> Please refer to the <rte_lcore_var.h> API documentation for both a
>> rationale for this new API, and a comparison to the alternatives
>> available.
>>
>> The adoption of this API would affect many different DPDK modules, but
>> the author updated only a few, mostly to serve as examples in this
>> RFC, and to iron out some, but surely not all, wrinkles in the API.
>>
>> The question on how to best allocate static per-lcore memory has been
>> up several times on the dev mailing list, for example in the thread on
>> "random: use per lcore state" RFC by Stephen Hemminger.
>>
>> Lcore variables are surely not the answer to all your per-lcore-data
>> needs, since it only allows for more-or-less static allocation. In the
>> author's opinion, it does however provide a reasonably simple and
>> clean and seemingly very much performant solution to a real problem.
> 
> This RFC is an improvement of the design pattern of allocating a RTE_MAX_LCORE sized array of structs per library, which typically introduces a lot of padding, and thus wastes L1 data cache.
> 
> I would like to see it as a patch getting into DPDK 24.11.
> 

I would be happy to develop and maintain this DPDK module.

I will submit this as a v1 PATCH.

>>
>> One thing is unclear to the author is how this API relates to a
>> potential future per-lcore dynamic allocator (e.g., a per-lcore heap).
> 
> Perfection is the enemy of progress.
> Let's consider this a 1:1 upgrade of a existing design pattern, and not worry about how to broaden its scope in the future.
> 
> -Morten
>