Re: [PATCH 2/5] net/mlx5: free buffers in bulk on Tx completion

["Nélio Laranjeiro" <nelio.laranjeiro@6wind.com>]

On Fri, Jun 30, 2017 at 02:30:47PM +0200, Nélio Laranjeiro wrote:
> On Wed, Jun 28, 2017 at 04:04:00PM -0700, Yongseok Koh wrote:
> > When processing Tx completion, it is more efficient to free buffers in bulk
> > using rte_mempool_put_bulk() if buffers are from a same mempool.
> > 
> > Signed-off-by: Yongseok Koh <yskoh@mellanox.com>
> > ---
> >  drivers/net/mlx5/mlx5_rxtx.c | 36 +++++++++++++++++++++++++++---------
> >  1 file changed, 27 insertions(+), 9 deletions(-)
> > 
> > diff --git a/drivers/net/mlx5/mlx5_rxtx.c b/drivers/net/mlx5/mlx5_rxtx.c
> > index 43db06ad8..d81d630f7 100644
> > --- a/drivers/net/mlx5/mlx5_rxtx.c
> > +++ b/drivers/net/mlx5/mlx5_rxtx.c
> > @@ -264,6 +264,8 @@ txq_complete(struct txq *txq)
> >  	uint16_t cq_ci = txq->cq_ci;
> >  	volatile struct mlx5_cqe *cqe = NULL;
> >  	volatile struct mlx5_wqe_ctrl *ctrl;
> > +	struct rte_mbuf *m, *free[elts_n];
> > +	unsigned int blk_n = 0;
> >  
> >  	do {
> >  		volatile struct mlx5_cqe *tmp;
> > @@ -296,21 +298,37 @@ txq_complete(struct txq *txq)
> >  	assert((elts_tail & elts_m) < (1 << txq->wqe_n));
> >  	/* Free buffers. */
> >  	while (elts_free != elts_tail) {
> > -		struct rte_mbuf *elt = (*txq->elts)[elts_free & elts_m];
> > -		struct rte_mbuf *elt_next =
> > -			(*txq->elts)[(elts_free + 1) & elts_m];
> > -
> > +		m = rte_pktmbuf_prefree_seg((*txq->elts)[elts_free++ & elts_m]);
> > +		if (likely(m != NULL)) {
> > +			if (blk_n) {
> > +				if (likely(m->pool == free[0]->pool)) {
> > +					free[blk_n++] = m;
> > +				} else {
> > +					rte_mempool_put_bulk(
> > +							free[0]->pool,
> > +							(void *)free,
> > +							blk_n);
> 
> The indentation is strange here, free[0] should be on the same line as
> rte_mempool_put_bulk.
> 
> > +					free[0] = m;
> > +					blk_n = 1;
> > +				}
> > +			} else {
> > +				free[0] = m;
> > +				blk_n = 1;
> > +			}
> > +		}
> 
> This loop could be smaller, blk_n can only be equal to 0 in the first
> iteration, otherwise is >= 1.
> The first if statement can be merged with the second one: 
> 
> 	if (likely(m != NULL)) {
> 		if (likely(blk_n && m->pool == free[0]->pool)) {

This condition is a wrong also, it should be !blk_n || (m->pool ...

Why don't you keep a pointer to the mpool (e.g. m->pool == pool)?  It
seems to cost a little to deference two pointers to reach the pool's
one.

Thanks,

-- 
Nélio Laranjeiro
6WIND