Hi Adrien
> -----Original Message-----
> From: Adrien Mazarguil [mailto:adrien.mazarg...@6wind.com]
> Sent: Wednesday, December 6, 2017 12:59 PM
> To: Matan Azrad <ma...@mellanox.com>
> Cc: dev@dpdk.org
> Subject: Re: [PATCH 7/8] net/mlx4: align Tx descriptors number
>
> On Tue, Nov 28, 2017 at 12:19:29PM +0000, Matan Azrad wrote:
> > Using power of 2 descriptors number makes the ring management easier
> > and allows to use mask operation instead of wraparound conditions.
> >
> > Adjust Tx descriptor number to be power of 2 and change calculation to
> > use mask accordingly.
> >
> > Signed-off-by: Matan Azrad <ma...@mellanox.com>
>
> A few minor comments, see below.
>
> > ---
> > drivers/net/mlx4/mlx4_rxtx.c | 22 ++++++++--------------
> > drivers/net/mlx4/mlx4_txq.c | 20 ++++++++++++--------
> > 2 files changed, 20 insertions(+), 22 deletions(-)
> >
> > diff --git a/drivers/net/mlx4/mlx4_rxtx.c
> > b/drivers/net/mlx4/mlx4_rxtx.c index 30f2930..b5aaf4c 100644
> > --- a/drivers/net/mlx4/mlx4_rxtx.c
> > +++ b/drivers/net/mlx4/mlx4_rxtx.c
> > @@ -314,7 +314,7 @@ struct pv {
> > * Pointer to Tx queue structure.
> > */
> > static void
> > -mlx4_txq_complete(struct txq *txq, const unsigned int elts_n,
> > +mlx4_txq_complete(struct txq *txq, const unsigned int elts_m,
> > struct mlx4_sq *sq)
>
> Documentation needs updating.
>
OK
> > {
> > unsigned int elts_tail = txq->elts_tail; @@ -355,13 +355,11 @@
> > struct pv {
> > if (unlikely(!completed))
> > return;
> > /* First stamping address is the end of the last one. */
> > - first_txbb = (&(*txq->elts)[elts_tail])->eocb;
> > + first_txbb = (&(*txq->elts)[elts_tail & elts_m])->eocb;
> > elts_tail += completed;
> > - if (elts_tail >= elts_n)
> > - elts_tail -= elts_n;
> > /* The new tail element holds the end address. */
> > sq->remain_size += mlx4_txq_stamp_freed_wqe(sq, first_txbb,
> > - (&(*txq->elts)[elts_tail])->eocb);
> > + (&(*txq->elts)[elts_tail & elts_m])->eocb);
> > /* Update CQ consumer index. */
> > cq->cons_index = cons_index;
> > *cq->set_ci_db = rte_cpu_to_be_32(cons_index &
> MLX4_CQ_DB_CI_MASK);
> > @@ -534,6 +532,7 @@ struct pv {
> > struct txq *txq = (struct txq *)dpdk_txq;
> > unsigned int elts_head = txq->elts_head;
> > const unsigned int elts_n = txq->elts_n;
> > + const unsigned int elts_m = elts_n - 1;
> > unsigned int bytes_sent = 0;
> > unsigned int i;
> > unsigned int max;
> > @@ -543,24 +542,20 @@ struct pv {
> >
> > assert(txq->elts_comp_cd != 0);
> > if (likely(txq->elts_comp != 0))
> > - mlx4_txq_complete(txq, elts_n, sq);
> > + mlx4_txq_complete(txq, elts_m, sq);
> > max = (elts_n - (elts_head - txq->elts_tail));
> > - if (max > elts_n)
> > - max -= elts_n;
> > assert(max >= 1);
> > assert(max <= elts_n);
> > /* Always leave one free entry in the ring. */
> > --max;
> > if (max > pkts_n)
> > max = pkts_n;
> > - elt = &(*txq->elts)[elts_head];
> > + elt = &(*txq->elts)[elts_head & elts_m];
> > /* First Tx burst element saves the next WQE control segment. */
> > ctrl = elt->wqe;
> > for (i = 0; (i != max); ++i) {
> > struct rte_mbuf *buf = pkts[i];
> > - unsigned int elts_head_next =
> > - (((elts_head + 1) == elts_n) ? 0 : elts_head + 1);
> > - struct txq_elt *elt_next = &(*txq->elts)[elts_head_next];
> > + struct txq_elt *elt_next = &(*txq->elts)[++elts_head &
> elts_m];
> > uint32_t owner_opcode = sq->owner_opcode;
> > volatile struct mlx4_wqe_data_seg *dseg =
> > (volatile struct mlx4_wqe_data_seg *)(ctrl +
> 1); @@ -678,7 +673,6
> > @@ struct pv {
> > ctrl->owner_opcode = rte_cpu_to_be_32(owner_opcode);
> > elt->buf = buf;
> > bytes_sent += buf->pkt_len;
> > - elts_head = elts_head_next;
> > ctrl = ctrl_next;
> > elt = elt_next;
> > }
> > @@ -694,7 +688,7 @@ struct pv {
> > rte_wmb();
> > /* Ring QP doorbell. */
> > rte_write32(txq->msq.doorbell_qpn, txq->msq.db);
> > - txq->elts_head = elts_head;
> > + txq->elts_head += i;
> > txq->elts_comp += i;
> > return i;
> > }
> > diff --git a/drivers/net/mlx4/mlx4_txq.c b/drivers/net/mlx4/mlx4_txq.c
> > index 4c7b62a..253075a 100644
> > --- a/drivers/net/mlx4/mlx4_txq.c
> > +++ b/drivers/net/mlx4/mlx4_txq.c
> > @@ -76,17 +76,16 @@
> > unsigned int elts_head = txq->elts_head;
> > unsigned int elts_tail = txq->elts_tail;
> > struct txq_elt (*elts)[txq->elts_n] = txq->elts;
> > + unsigned int elts_m = txq->elts_n - 1;
> >
> > DEBUG("%p: freeing WRs", (void *)txq);
> > while (elts_tail != elts_head) {
> > - struct txq_elt *elt = &(*elts)[elts_tail];
> > + struct txq_elt *elt = &(*elts)[elts_tail++ & elts_m];
> >
> > assert(elt->buf != NULL);
> > rte_pktmbuf_free(elt->buf);
> > elt->buf = NULL;
> > elt->wqe = NULL;
> > - if (++elts_tail == RTE_DIM(*elts))
> > - elts_tail = 0;
> > }
> > txq->elts_tail = txq->elts_head;
> > }
> > @@ -208,7 +207,9 @@ struct txq_mp2mr_mbuf_check_data {
> > struct mlx4dv_obj mlxdv;
> > struct mlx4dv_qp dv_qp;
> > struct mlx4dv_cq dv_cq;
> > - struct txq_elt (*elts)[desc];
> > + uint32_t elts_size = desc > 0x1000 ? 0x1000 :
> > + rte_align32pow2((uint32_t)desc);
>
> Where is that magical 0x1000 value coming from? It should at least come
> through a macro definition.
>
> > + struct txq_elt (*elts)[elts_size];
> > struct ibv_qp_init_attr qp_init_attr;
> > struct txq *txq;
> > uint8_t *bounce_buf;
> > @@ -247,11 +248,14 @@ struct txq_mp2mr_mbuf_check_data {
> > (void *)dev, idx);
> > return -rte_errno;
> > }
> > - if (!desc) {
> > - rte_errno = EINVAL;
> > - ERROR("%p: invalid number of Tx descriptors", (void *)dev);
> > - return -rte_errno;
> > + if ((uint32_t)desc != elts_size) {
> > + desc = (uint16_t)elts_size;
> > + WARN("%p: changed number of descriptors in TX queue %u"
> > + " to be power of two (%d)",
> > + (void *)dev, idx, desc);
>
> You should display the same message as in mlx4_rxq.c for consistency (also
> TX => Tx).
>
OK
> > }
> > + DEBUG("%p: configuring queue %u for %u descriptors",
> > + (void *)dev, idx, desc);
>
> Unnecessary duplicated debugging message already printed at the beginning
> of this function. Yes this is a different value but WARN() made that pretty
> clear.
>
> > /* Allocate and initialize Tx queue. */
> > mlx4_zmallocv_socket("TXQ", vec, RTE_DIM(vec), socket);
> > if (!txq) {
> > --
> > 1.8.3.1
> >
>
> --
> Adrien Mazarguil
> 6WIND
