[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 <yskoh at mellanox.com>
Acked-by: Nelio Laranjeiro <nelio.laranjeiro at 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