RE: [PATCH] net/intel: allow fast-free to empty cache

["Morten Brørup" <mb@smartsharesystems.com>]

> From: Bruce Richardson [mailto:bruce.richardson@intel.com]
> Sent: Monday, 10 March 2025 16.27
> 
> On Mon, Mar 10, 2025 at 04:18:35PM +0100, Morten Brørup wrote:
> > > From: Bruce Richardson [mailto:bruce.richardson@intel.com]
> > > Sent: Monday, 10 March 2025 14.26
> > >
> > > When freeing transmitted mbufs, there is no reason to send the
> freed
> > > mbufs directly to the ring if the cache is empty - only if it is
> zero
> > > size (in which case the cache pointer is NULL). Therefore, remove
> the
> > > empty check and only check for a null cache pointer.
> > >
> > > Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
> > > ---
> > >  drivers/net/intel/common/tx.h | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/net/intel/common/tx.h
> > > b/drivers/net/intel/common/tx.h
> > > index d9cf4474fc..d361fe64ab 100644
> > > --- a/drivers/net/intel/common/tx.h
> > > +++ b/drivers/net/intel/common/tx.h
> > > @@ -143,7 +143,7 @@ ci_tx_free_bufs_vec(struct ci_tx_queue *txq,
> > > ci_desc_done_fn desc_done, bool ctx
> > >  		void **cache_objs;
> > >  		struct rte_mempool_cache *cache =
> > > rte_mempool_default_cache(mp, rte_lcore_id());
> > >
> > > -		if (!cache || cache->len == 0)
> > > +		if (cache == NULL)
> > >  			goto normal;
> > >
> > >  		cache_objs = &cache->objs[cache->len];
> > > --
> > > 2.43.0
> >
> > Yep, it did look strange.
> > Reviewed-by: Morten Brørup <mb@smartsharesystems.com>
> >
> Thanks for review.

BTW, I recall other Intel drivers having the same "feature":
https://elixir.bootlin.com/dpdk/v24.11.1/source/drivers/net/iavf/iavf_rxtx_vec_avx512.c#L1876
https://elixir.bootlin.com/dpdk/v24.11.1/source/drivers/net/ice/ice_rxtx_vec_avx512.c#L891

> 
> FYI: Given that this is in a sensitive area and we are now past rc2,
> I'm going
> to postponse merging this patch till 25.07, rather than risk it in
> 25.03.

Agree.

> 
> /Bruce