[PATCH 2/3] power: defer lcore variable allocation

[David Marchand]

On Fri, Dec 6, 2024 at 12:29 PM Mattias Rönnblom <hofors at lysator.liu.se> wrote:
> I would wrap all RTE_LCORE_VAR_LCORE() and RTE_LCORE_VAR().
>
> static struct pmd_core_cfg *
> get_cfg_lcore(unsigned int lcore_id)
> {
>         assure_lcore_cfgs_alloced();
>         return RTE_LCORE_VAR_LCORE(lcore_cfgs, lcore_id);
> }
>
> static struct pmd_core_cfg *
> get_cfg(void)
> {
>         get_cfg_lcore(rte_lcore_id());
> }
>
> Add
>
> static void
> assure_lcore_cfgs_alloced(unsigned int lcore_id)
> {
>         if (lcore_cfgs != NULL)

==

>                 lcore_cfgs_alloc();
> }
>
> ..or maybe better merge assure_lcore_cfgs_alloced() and lcore_cfgs_alloc().
>
> Makes it a little harder to make mistakes.

clb_multiwait, clb_pause and clb_scale_freq callbacks can only be
reached after a successful call to
rte_power_ethdev_pmgmt_queue_enable.
Triggering an allocation in them means we are hiding a (internal)
programatic error as allocation and use of a lcore variable are
clearly separated atm.
If we keep the lcore var api as is, I would add an assert() (maybe
under a debug build option) in RTE_LCORE_VAR macros themselves, as
calling with a NULL handle means the initialisation path in some
code/RTE_LCORE_VAR API use was incorrect.


Or because you propose to add the same type of helpers in both this
patch and the next, I am considering the other way: hide the
allocation in the RTE_LCORE_VAR* macros.
Checking for already allocated var in RTE_LCORE_VAR_ALLOC seems fine.
But the "fast path" RTE_LCORE_VAR would have an unwanted branch in most cases.


> A somewhat unrelated question: why is pmd_core_cfg cache-line aligned? I
> don't think it should be.

Before the conversion to per lcore variable, it was probably useful
(avoiding false sharing).
With the conversion, indeed, it looks like a waste of space.
It seems worth a separate fix.


-- 
David Marchand