RE: [PATCH 4/4] mempool: use lcore API to check if lcore ID is valid

[Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>]

<snip>
> 
> 
> 
> >
> > Use lcore API to check if the lcore ID is valid. The runtime check
> > does not add much value.
> 
> From my perspective it adds a perfect value:
> Only threads with valid lcore id have their own default mempool cache.
The threads would call 'rte_lcore_id()' to return their lcore_id. This ensures the lcore_id is valid already. Why do we need to check it again in rte_mempool_default_cache? Why would a thread use an incorrect lcore_id?

> 
> > Hence use assert to validate
> > the lcore ID.
> 
> Wonder why?
> What's wrong for the thread to try to get default mempool cache?
What are the cases where a thread does not know that it is not an EAL thread and call rte_mempool_default_cache with a random lcore_id?
Since, this API is called in the data plane, it makes sense to remove any additional validations.

> That would change existing behavior and in general seems wrong to me.
Agree on the change in existing behavior. We can discuss this once we agree/disagree on the above.

> So I am strongly opposed.
> 
> > Signed-off-by: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>
> > Reviewed-by: Wathsala Vithanage <wathsala.vithanage@arm.com>
> > Reviewed-by: Ruifeng Wang <ruifeng.wang@arm.com>
> > ---
> >  lib/mempool/rte_mempool.h | 5 ++---
> >  1 file changed, 2 insertions(+), 3 deletions(-)
> >
> > diff --git a/lib/mempool/rte_mempool.h b/lib/mempool/rte_mempool.h
> > index 009bd10215..00c5aa961b 100644
> > --- a/lib/mempool/rte_mempool.h
> > +++ b/lib/mempool/rte_mempool.h
> > @@ -1314,10 +1314,9 @@ rte_mempool_cache_free(struct
> rte_mempool_cache
> > *cache);  static __rte_always_inline struct rte_mempool_cache *
> > rte_mempool_default_cache(struct rte_mempool *mp, unsigned lcore_id)
> > {
> > -	if (mp->cache_size == 0)
> > -		return NULL;
> > +	RTE_ASSERT(rte_lcore_id_is_valid(lcore_id));
> >
> > -	if (lcore_id >= RTE_MAX_LCORE)
> > +	if (mp->cache_size == 0)
> >  		return NULL;
> >
> >  	rte_mempool_trace_default_cache(mp, lcore_id,
> > --
> > 2.25.1
> >