On 2024-09-02 16:42, Morten Brørup wrote:
From: Mattias Rönnblom [mailto:mattias.ronnb...@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
