[dpdk-dev] [PATCH 04/11] net/mlx5: support mbuf headroom for LRO packet

[Matan Azrad]

Patch [1] zeroes the mbuf headroom when the port is configured with LRO
because when working with more than one stride per packet the HW cannot
guaranty an headroom in the start stride of each packet.

Change the solution to support mbuf headroom by adding an empty buffer
as the first packet segment, scatter mode must be enabled to support it.

[1] http://patches.dpdk.org/patch/56912/

Signed-off-by: Matan Azrad <matan at mellanox.com>
Acked-by: Viacheslav Ovsiienko <viacheslavo at mellanox.com>
---
 doc/guides/nics/mlx5.rst     |  3 +--
 drivers/net/mlx5/mlx5_rxq.c  | 24 ++++++++++++++++--------
 drivers/net/mlx5/mlx5_rxtx.c | 22 +++++++++++++++++++++-
 3 files changed, 38 insertions(+), 11 deletions(-)

diff --git a/doc/guides/nics/mlx5.rst b/doc/guides/nics/mlx5.rst
index 92f1b97..cd550f4 100644
--- a/doc/guides/nics/mlx5.rst
+++ b/doc/guides/nics/mlx5.rst
@@ -165,8 +165,7 @@ Limitations
 
 - LRO:
 
-  - No mbuf headroom space is created for RX packets when LRO is configured.
-  - ``scatter_fcs`` is disabled when LRO is configured.
+  - scatter_fcs is disabled when LRO is configured.
 
 Statistics
 ----------
diff --git a/drivers/net/mlx5/mlx5_rxq.c b/drivers/net/mlx5/mlx5_rxq.c
index bd26ee2..d10c5c1 100644
--- a/drivers/net/mlx5/mlx5_rxq.c
+++ b/drivers/net/mlx5/mlx5_rxq.c
@@ -1599,12 +1599,7 @@ struct mlx5_rxq_ctrl *
 	unsigned int mb_len = rte_pktmbuf_data_room_size(mp);
 	unsigned int mprq_stride_size;
 	struct mlx5_dev_config *config = &priv->config;
-	/*
-	 * LRO packet may consume all the stride memory, hence we cannot
-	 * guaranty head-room. A new striding RQ feature may be added in CX6 DX
-	 * to allow head-room and tail-room for the LRO packets.
-	 */
-	unsigned int strd_headroom_en = mlx5_lro_on(dev) ? 0 : 1;
+	unsigned int strd_headroom_en;
 	/*
 	 * Always allocate extra slots, even if eventually
 	 * the vector Rx will not be used.
@@ -1645,6 +1640,21 @@ struct mlx5_rxq_ctrl *
 	if (dev->data->dev_conf.intr_conf.rxq)
 		tmpl->irq = 1;
 	/*
+	 * LRO packet may consume all the stride memory, hence we cannot
+	 * guaranty head-room near the packet memory in the stride.
+	 * In this case scatter is, for sure, enabled and an empty mbuf may be
+	 * added in the start for the head-room.
+	 */
+	if (mlx5_lro_on(dev) && RTE_PKTMBUF_HEADROOM > 0 &&
+	    non_scatter_min_mbuf_size > mb_len) {
+		strd_headroom_en = 0;
+		mprq_stride_size = RTE_MIN(max_rx_pkt_len,
+					1u << config->mprq.max_stride_size_n);
+	} else {
+		strd_headroom_en = 1;
+		mprq_stride_size = non_scatter_min_mbuf_size;
+	}
+	/*
 	 * This Rx queue can be configured as a Multi-Packet RQ if all of the
 	 * following conditions are met:
 	 *  - MPRQ is enabled.
@@ -1653,8 +1663,6 @@ struct mlx5_rxq_ctrl *
 	 *    stride.
 	 *  Otherwise, enable Rx scatter if necessary.
 	 */
-	mprq_stride_size = max_rx_pkt_len + RTE_PKTMBUF_HEADROOM *
-				strd_headroom_en;
 	if (mprq_en &&
 	    desc > (1U << config->mprq.stride_num_n) &&
 	    mprq_stride_size <= (1U << config->mprq.max_stride_size_n)) {
diff --git a/drivers/net/mlx5/mlx5_rxtx.c b/drivers/net/mlx5/mlx5_rxtx.c
index a7ec73d..003eefd 100644
--- a/drivers/net/mlx5/mlx5_rxtx.c
+++ b/drivers/net/mlx5/mlx5_rxtx.c
@@ -1639,6 +1639,7 @@ enum mlx5_txcmp_code {
 				continue;
 			}
 			rte_memcpy(rte_pktmbuf_mtod(pkt, void *), addr, len);
+			DATA_LEN(pkt) = len;
 		} else {
 			rte_iova_t buf_iova;
 			struct rte_mbuf_ext_shared_info *shinfo;
@@ -1679,6 +1680,26 @@ enum mlx5_txcmp_code {
 				++rxq->stats.idropped;
 				continue;
 			}
+			DATA_LEN(pkt) = len;
+			/*
+			 * LRO packet may consume all the stride memory, in this
+			 * case packet head-room space is not guaranteed so must
+			 * to add an empty mbuf for the head-room.
+			 */
+			if (!rxq->strd_headroom_en) {
+				struct rte_mbuf *headroom_mbuf =
+						rte_pktmbuf_alloc(rxq->mp);
+
+				if (unlikely(headroom_mbuf == NULL)) {
+					rte_pktmbuf_free_seg(pkt);
+					++rxq->stats.rx_nombuf;
+					break;
+				}
+				PORT(pkt) = rxq->port_id;
+				NEXT(headroom_mbuf) = pkt;
+				pkt = headroom_mbuf;
+				NB_SEGS(pkt) = 2;
+			}
 		}
 		rxq_cq_to_mbuf(rxq, pkt, cqe, rss_hash_res);
 		if (lro_num_seg > 1) {
@@ -1687,7 +1708,6 @@ enum mlx5_txcmp_code {
 			pkt->tso_segsz = strd_sz;
 		}
 		PKT_LEN(pkt) = len;
-		DATA_LEN(pkt) = len;
 		PORT(pkt) = rxq->port_id;
 #ifdef MLX5_PMD_SOFT_COUNTERS
 		/* Increment bytes counter. */
-- 
1.8.3.1