net/mlx5: remove inefficient prefetching

Prefetching completion queue entries is inefficient because too few CPU
cycles are spent before their use, which results into cache misses anyway.

Signed-off-by: Nelio Laranjeiro <nelio.laranjeiro@6wind.com>
Acked-by: Adrien Mazarguil <adrien.mazarguil@6wind.com>

diff --git a/drivers/net/mlx5/mlx5_rxtx.c b/drivers/net/mlx5/mlx5_rxtx.c
index 380d137..9820f72 100644 (file)
--- a/drivers/net/mlx5/mlx5_rxtx.c
+++ b/drivers/net/mlx5/mlx5_rxtx.c
@@ -345,23 +345,6 @@ mlx5_tx_dbrec(struct txq *txq)
        txq->bf_offset ^= (1 << txq->bf_buf_size);
 }
 
-/**
- * Prefetch a CQE.
- *
- * @param txq
- *   Pointer to TX queue structure.
- * @param cqe_ci
- *   CQE consumer index.
- */
-static inline void
-tx_prefetch_cqe(struct txq *txq, uint16_t ci)
-{
-       volatile struct mlx5_cqe *cqe;
-
-       cqe = &(*txq->cqes)[ci & ((1 << txq->cqe_n) - 1)];
-       rte_prefetch0(cqe);
-}
-
 /**
  * DPDK callback for TX.
  *
@@ -393,8 +376,6 @@ mlx5_tx_burst(void *dpdk_txq, struct rte_mbuf **pkts, uint16_t pkts_n)
        if (unlikely(!pkts_n))
                return 0;
        /* Prefetch first packet cacheline. */
-       tx_prefetch_cqe(txq, txq->cq_ci);
-       tx_prefetch_cqe(txq, txq->cq_ci + 1);
        rte_prefetch0(*pkts);
        /* Start processing. */
        txq_complete(txq);
@@ -732,7 +713,6 @@ mlx5_tx_burst_mpw(void *dpdk_txq, struct rte_mbuf **pkts, uint16_t pkts_n)
        if (unlikely(!pkts_n))
                return 0;
        /* Prefetch first packet cacheline. */
-       tx_prefetch_cqe(txq, txq->cq_ci);
        rte_prefetch0(tx_mlx5_wqe(txq, txq->wqe_ci));
        rte_prefetch0(tx_mlx5_wqe(txq, txq->wqe_ci + 1));
        /* Start processing. */
@@ -937,7 +917,6 @@ mlx5_tx_burst_mpw_inline(void *dpdk_txq, struct rte_mbuf **pkts,
        if (unlikely(!pkts_n))
                return 0;
        /* Prefetch first packet cacheline. */
-       tx_prefetch_cqe(txq, txq->cq_ci);
        rte_prefetch0(tx_mlx5_wqe(txq, txq->wqe_ci));
        rte_prefetch0(tx_mlx5_wqe(txq, txq->wqe_ci + 1));
        /* Start processing. */