net/mlx5: change error-prone code on Tx path

In the main loop of mlx5_tx_burst(), pointers/indexes are advanced at the
beginning. Therefore, those should be rolled back if checking resource
availability fails and breaks the loop. And some of them are even
redundant.

Signed-off-by: Yongseok Koh <yskoh@mellanox.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 cf63434..de6e0fa 100644 (file)
--- a/drivers/net/mlx5/mlx5_rxtx.c
+++ b/drivers/net/mlx5/mlx5_rxtx.c
@@ -538,7 +538,7 @@ mlx5_tx_burst(void *dpdk_txq, struct rte_mbuf **pkts, uint16_t pkts_n)
 #endif
 
                /* first_seg */
-               buf = *(pkts++);
+               buf = *pkts;
                segs_n = buf->nb_segs;
                /*
                 * Make sure there is enough room to store this packet and
@@ -549,15 +549,13 @@ mlx5_tx_burst(void *dpdk_txq, struct rte_mbuf **pkts, uint16_t pkts_n)
                        break;
                max -= segs_n;
                --segs_n;
-               if (!segs_n)
-                       --pkts_n;
                if (unlikely(--max_wqe == 0))
                        break;
                wqe = (volatile struct mlx5_wqe_v *)
                        tx_mlx5_wqe(txq, txq->wqe_ci);
                rte_prefetch0(tx_mlx5_wqe(txq, txq->wqe_ci + 1));
-               if (pkts_n > 1)
-                       rte_prefetch0(*pkts);
+               if (pkts_n - i > 1)
+                       rte_prefetch0(*(pkts + 1));
                addr = rte_pktmbuf_mtod(buf, uintptr_t);
                length = DATA_LEN(buf);
                ehdr = (((uint8_t *)addr)[1] << 8) |
@@ -569,14 +567,10 @@ mlx5_tx_burst(void *dpdk_txq, struct rte_mbuf **pkts, uint16_t pkts_n)
                        break;
                /* Update element. */
                (*txq->elts)[elts_head] = buf;
-               elts_head = (elts_head + 1) & (elts_n - 1);
                /* Prefetch next buffer data. */
-               if (pkts_n > 1) {
-                       volatile void *pkt_addr;
-
-                       pkt_addr = rte_pktmbuf_mtod(*pkts, volatile void *);
-                       rte_prefetch0(pkt_addr);
-               }
+               if (pkts_n - i > 1)
+                       rte_prefetch0(
+                           rte_pktmbuf_mtod(*(pkts + 1), volatile void *));
                /* Should we enable HW CKSUM offload */
                if (buf->ol_flags &
                    (PKT_TX_IP_CKSUM | PKT_TX_TCP_CKSUM | PKT_TX_UDP_CKSUM)) {
@@ -679,10 +673,6 @@ mlx5_tx_burst(void *dpdk_txq, struct rte_mbuf **pkts, uint16_t pkts_n)
                                        };
                                        ds = 1;
                                        total_length = 0;
-                                       pkts--;
-                                       pkts_n++;
-                                       elts_head = (elts_head - 1) &
-                                                   (elts_n - 1);
                                        k++;
                                        goto next_wqe;
                                }
@@ -815,17 +805,17 @@ next_seg:
                        naddr,
                        naddr >> 32,
                };
-               (*txq->elts)[elts_head] = buf;
                elts_head = (elts_head + 1) & (elts_n - 1);
+               (*txq->elts)[elts_head] = buf;
                ++sg;
                /* Advance counter only if all segs are successfully posted. */
-               if (sg < segs_n) {
+               if (sg < segs_n)
                        goto next_seg;
-               } else {
-                       --pkts_n;
+               else
                        j += sg;
-               }
 next_pkt:
+               elts_head = (elts_head + 1) & (elts_n - 1);
+               ++pkts;
                ++i;
                /* Initialize known and common part of the WQE structure. */
                if (tso) {
@@ -863,7 +853,7 @@ next_wqe:
                /* Increment sent bytes counter. */
                txq->stats.obytes += total_length;
 #endif
-       } while (pkts_n);
+       } while (i < pkts_n);
        /* Take a shortcut if nothing must be sent. */
        if (unlikely((i + k) == 0))
                return 0;