[dpdk-dev] [PATCH] net/mlx5: poll completion queue once per a call

[Yongseok Koh]

mlx5_tx_complete() polls completion queue multiple times until it
encounters an invalid entry. As Tx completions are suppressed by
MLX5_TX_COMP_THRESH, it is waste of cycles to expect multiple completions
in a poll. And freeing too many buffers in a call can cause high jitter.
This patch improves throughput a little.

Signed-off-by: Yongseok Koh <ys...@mellanox.com>
Acked-by: Nelio Laranjeiro <nelio.laranje...@6wind.com>
---
 drivers/net/mlx5/mlx5_rxtx.h | 32 ++++++++++----------------------
 1 file changed, 10 insertions(+), 22 deletions(-)

diff --git a/drivers/net/mlx5/mlx5_rxtx.h b/drivers/net/mlx5/mlx5_rxtx.h
index 534aaeb46..7fd59a4b1 100644
--- a/drivers/net/mlx5/mlx5_rxtx.h
+++ b/drivers/net/mlx5/mlx5_rxtx.h
@@ -480,30 +480,18 @@ mlx5_tx_complete(struct txq *txq)
        struct rte_mempool *pool = NULL;
        unsigned int blk_n = 0;
 
-       do {
-               volatile struct mlx5_cqe *tmp;
-
-               tmp = &(*txq->cqes)[cq_ci & cqe_cnt];
-               if (check_cqe(tmp, cqe_n, cq_ci))
-                       break;
-               cqe = tmp;
+       cqe = &(*txq->cqes)[cq_ci & cqe_cnt];
+       if (unlikely(check_cqe(cqe, cqe_n, cq_ci)))
+               return;
 #ifndef NDEBUG
-               if (MLX5_CQE_FORMAT(cqe->op_own) == MLX5_COMPRESSED) {
-                       if (!check_cqe_seen(cqe))
-                               ERROR("unexpected compressed CQE, TX stopped");
-                       return;
-               }
-               if ((MLX5_CQE_OPCODE(cqe->op_own) == MLX5_CQE_RESP_ERR) ||
-                   (MLX5_CQE_OPCODE(cqe->op_own) == MLX5_CQE_REQ_ERR)) {
-                       if (!check_cqe_seen(cqe))
-                               ERROR("unexpected error CQE, TX stopped");
-                       return;
-               }
-#endif /* NDEBUG */
-               ++cq_ci;
-       } while (1);
-       if (unlikely(cqe == NULL))
+       if ((MLX5_CQE_OPCODE(cqe->op_own) == MLX5_CQE_RESP_ERR) ||
+           (MLX5_CQE_OPCODE(cqe->op_own) == MLX5_CQE_REQ_ERR)) {
+               if (!check_cqe_seen(cqe))
+                       ERROR("unexpected error CQE, TX stopped");
                return;
+       }
+#endif /* NDEBUG */
+       ++cq_ci;
        txq->wqe_pi = ntohs(cqe->wqe_counter);
        ctrl = (volatile struct mlx5_wqe_ctrl *)
                tx_mlx5_wqe(txq, txq->wqe_pi);
-- 
2.11.0