[dpdk-stable] [PATCH 19.11 v2] net/mlx5: fix multi-segment inline for the first segments

[Bing Zhao <bingz@nvidia.com>]

From: Viacheslav Ovsiienko <viacheslavo@nvidia.com>

[ upstream commit ec837ad0fc7c6df4912cc2706b9cd54b225f4a34 ]

Before 19.08 release the Tx burst routines of mlx5 PMD
provided data inline for the first short segments of the
multi-segment packets. In the release 19.08 mlx5 Tx datapath
was refactored and this behavior was broken, affecting the
performance.

For example, the T-Rex traffic generator might use small
leading segments to handle packet headers and performance
degradation was noticed.

If the first segments of the multi-segment packet are short
and the overall length is below the inline threshold it
should be inline into the WQE to fix the performance.

Fixes: 18a1c20044c0 ("net/mlx5: implement Tx burst template")
Cc: stable@dpdk.org

Signed-off-by: Viacheslav Ovsiienko <viacheslavo@nvidia.com>
Signed-off-by: Bing Zhao <bingz@nvidia.com>
---
 drivers/net/mlx5/mlx5_rxtx.c | 26 ++++++++++++--------------
 1 file changed, 12 insertions(+), 14 deletions(-)

diff --git a/drivers/net/mlx5/mlx5_rxtx.c b/drivers/net/mlx5/mlx5_rxtx.c
index 73dbf68d2b..8a6162ebd6 100644
--- a/drivers/net/mlx5/mlx5_rxtx.c
+++ b/drivers/net/mlx5/mlx5_rxtx.c
@@ -3336,6 +3336,8 @@ mlx5_tx_packet_multi_inline(struct mlx5_txq_data *restrict txq,
 		unsigned int nxlen;
 		uintptr_t start;
 
+		mbuf = loc->mbuf;
+		nxlen = rte_pktmbuf_data_len(mbuf);
 		/*
 		 * Packet length exceeds the allowed inline
 		 * data length, check whether the minimal
@@ -3345,27 +3347,22 @@ mlx5_tx_packet_multi_inline(struct mlx5_txq_data *restrict txq,
 			assert(txq->inlen_mode >= MLX5_ESEG_MIN_INLINE_SIZE);
 			assert(txq->inlen_mode <= txq->inlen_send);
 			inlen = txq->inlen_mode;
-		} else {
-			if (!vlan || txq->vlan_en) {
-				/*
-				 * VLAN insertion will be done inside by HW.
-				 * It is not utmost effective - VLAN flag is
-				 * checked twice, but we should proceed the
-				 * inlining length correctly and take into
-				 * account the VLAN header being inserted.
-				 */
-				return mlx5_tx_packet_multi_send
-							(txq, loc, olx);
-			}
+		} else if (vlan && !txq->vlan_en) {
+			/*
+			 * VLAN insertion is requested and hardware does not
+			 * support the offload, will do with software inline.
+			 */
 			inlen = MLX5_ESEG_MIN_INLINE_SIZE;
+		} else if (nxlen > txq->inlen_send) {
+			return mlx5_tx_packet_multi_send(txq, loc, olx);
+		} else {
+			goto do_first;
 		}
 		/*
 		 * Now we know the minimal amount of data is requested
 		 * to inline. Check whether we should inline the buffers
 		 * from the chain beginning to eliminate some mbufs.
 		 */
-		mbuf = loc->mbuf;
-		nxlen = rte_pktmbuf_data_len(mbuf);
 		if (unlikely(nxlen <= txq->inlen_send)) {
 			/* We can inline first mbuf at least. */
 			if (nxlen < inlen) {
@@ -3387,6 +3384,7 @@ mlx5_tx_packet_multi_inline(struct mlx5_txq_data *restrict txq,
 					goto do_align;
 				}
 			}
+do_first:
 			do {
 				inlen = nxlen;
 				mbuf = NEXT(mbuf);
-- 
2.25.1