mlx5: prefetch next Tx mbuf header and data

This change improves performance noticeably.

Signed-off-by: Nelio Laranjeiro <nelio.laranjeiro@6wind.com>

diff --git a/drivers/net/mlx5/mlx5_rxtx.c b/drivers/net/mlx5/mlx5_rxtx.c
index 7585570..bee5ce2 100644 (file)
--- a/drivers/net/mlx5/mlx5_rxtx.c
+++ b/drivers/net/mlx5/mlx5_rxtx.c
@@ -443,8 +443,11 @@ mlx5_tx_burst(void *dpdk_txq, struct rte_mbuf **pkts, uint16_t pkts_n)
        unsigned int i;
        unsigned int max;
        int err;
+       struct rte_mbuf *buf = pkts[0];
 
        assert(elts_comp_cd != 0);
+       /* Prefetch first packet cacheline. */
+       rte_prefetch0(buf);
        txq_complete(txq);
        max = (elts_n - (elts_head - txq->elts_tail));
        if (max > elts_n)
@@ -458,7 +461,7 @@ mlx5_tx_burst(void *dpdk_txq, struct rte_mbuf **pkts, uint16_t pkts_n)
        if (max > pkts_n)
                max = pkts_n;
        for (i = 0; (i != max); ++i) {
-               struct rte_mbuf *buf = pkts[i];
+               struct rte_mbuf *buf_next = pkts[i + 1];
                unsigned int elts_head_next =
                        (((elts_head + 1) == elts_n) ? 0 : elts_head + 1);
                struct txq_elt *elt_next = &(*txq->elts)[elts_head_next];
@@ -481,6 +484,8 @@ mlx5_tx_burst(void *dpdk_txq, struct rte_mbuf **pkts, uint16_t pkts_n)
                                tmp = next;
                        } while (tmp != NULL);
                }
+               if (i + 1 < max)
+                       rte_prefetch0(buf_next);
                /* Request TX completion. */
                if (unlikely(--elts_comp_cd == 0)) {
                        elts_comp_cd = txq->elts_comp_cd_init;
@@ -502,6 +507,7 @@ mlx5_tx_burst(void *dpdk_txq, struct rte_mbuf **pkts, uint16_t pkts_n)
                        uintptr_t addr;
                        uint32_t length;
                        uint32_t lkey;
+                       uintptr_t buf_next_addr;
 
                        /* Retrieve buffer information. */
                        addr = rte_pktmbuf_mtod(buf, uintptr_t);
@@ -522,6 +528,13 @@ mlx5_tx_burst(void *dpdk_txq, struct rte_mbuf **pkts, uint16_t pkts_n)
                                rte_prefetch0((volatile void *)
                                              (uintptr_t)addr);
                        RTE_MBUF_PREFETCH_TO_FREE(elt_next->buf);
+                       /* Prefetch next buffer data. */
+                       if (i + 1 < max) {
+                               buf_next_addr =
+                                       rte_pktmbuf_mtod(buf_next, uintptr_t);
+                               rte_prefetch0((volatile void *)
+                                             (uintptr_t)buf_next_addr);
+                       }
                        /* Put packet into send queue. */
 #if MLX5_PMD_MAX_INLINE > 0
                        if (length <= txq->max_inline)
@@ -571,6 +584,7 @@ mlx5_tx_burst(void *dpdk_txq, struct rte_mbuf **pkts, uint16_t pkts_n)
 #endif /* MLX5_PMD_SGE_WR_N > 1 */
                }
                elts_head = elts_head_next;
+               buf = buf_next;
 #ifdef MLX5_PMD_SOFT_COUNTERS
                /* Increment sent bytes counter. */
                txq->stats.obytes += sent_size;