[dpdk-dev] [PATCH] net/mlx5: fix external buffer pool registration for Rx queue

Viacheslav Ovsiienko viacheslavo at nvidia.com
Fri Feb 12 12:06:30 CET 2021

On Rx queue creation the mlx5 PMD registers the data buffers of the
specified pools for DMA operations. It scans the mem_list of the pools
and creates the MRs (DMA related NIC objects) for the chunks found.
If the pool is created with rte_pktmbuf_pool_create_extbuf() and
refers to the external attached buffers (whose are in the area of
application responsibility and it should explicitly register the
data buffer memory for DMA with rte_dev_dma_map() call) the chunks
contain the mbuf structures only, w/o any built-in data buffers.
Hence, DMA with mlx5 NIC never happens to this area and there is
no need to create MRs for these ones.

The extra not needed MRs were created for the pools with external
buffers causing MR cache load and performance was slightly affected.
The patch checks the mbuf pool type and skips MR creation for the
pools with external buffers.

Fixes: bdb8e5b1ea7b ("net/mlx5: allow allocated mbuf with external buffer")
Cc: stable at dpdk.org

Signed-off-by: Viacheslav Ovsiienko <viacheslavo at nvidia.com>
 drivers/net/mlx5/mlx5_mr.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/drivers/net/mlx5/mlx5_mr.c b/drivers/net/mlx5/mlx5_mr.c
index 8b20ee3f83..da4e91fc24 100644
--- a/drivers/net/mlx5/mlx5_mr.c
+++ b/drivers/net/mlx5/mlx5_mr.c
@@ -535,7 +535,18 @@ mlx5_mr_update_mp(struct rte_eth_dev *dev, struct mlx5_mr_ctrl *mr_ctrl,
 		.mr_ctrl = mr_ctrl,
 		.ret = 0,
+	uint32_t flags = rte_pktmbuf_priv_flags(mp);
+		/*
+		 * The pinned external buffer should be registered for DMA
+		 * operations by application. The mem_list of the pool contains
+		 * the list of chunks with mbuf structures w/o built-in data
+		 * buffers and DMA actually does not happen there, no need
+		 * to create MR for these chunks.
+		 */
+		return 0;
+	}
 	DRV_LOG(DEBUG, "Port %u Rx queue registering mp %s "
 		       "having %u chunks.", dev->data->port_id,
 		       mp->name, mp->nb_mem_chunks);

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