[dpdk-dev] [PATCH] net/mlx4: verify Tx max sges

[Moti Haimovsky <motih@mellanox.com>]

Max number of Tx scatter-gather entries is a property of the device
and is queried at init. This value was not changed in a while and
most probably will not be changed in the future, Therefore and
in order to enhance Tx performance, the Tx max-sge value is hardcoded
in mlx4 PRM code.
This patch adds a verification that the above assumption still holds
and that the hardcoded value is still supported by the mlx4 hardware.

Signed-off-by: Moti Haimovsky <motih@mellanox.com>
---
 drivers/net/mlx4/mlx4.c     | 1 +
 drivers/net/mlx4/mlx4_prm.h | 5 ++++-
 2 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/net/mlx4/mlx4.c b/drivers/net/mlx4/mlx4.c
index 4bc4a6f..61c5bf4 100644
--- a/drivers/net/mlx4/mlx4.c
+++ b/drivers/net/mlx4/mlx4.c
@@ -505,6 +505,7 @@ struct mlx4_conf {
 		rte_errno = ENODEV;
 		goto error;
 	}
+	assert(device_attr.max_sge >= MLX4_MAX_SGE);
 	for (i = 0; i < device_attr.phys_port_cnt; i++) {
 		uint32_t port = i + 1; /* ports are indexed from one */
 		struct ibv_context *ctx = NULL;
diff --git a/drivers/net/mlx4/mlx4_prm.h b/drivers/net/mlx4/mlx4_prm.h
index 217ea50..b382d59 100644
--- a/drivers/net/mlx4/mlx4_prm.h
+++ b/drivers/net/mlx4/mlx4_prm.h
@@ -53,7 +53,10 @@
 #define MLX4_TXBB_SIZE (1 << MLX4_TXBB_SHIFT)
 
 /* Typical TSO descriptor with 16 gather entries is 352 bytes. */
-#define MLX4_MAX_WQE_SIZE 512
+#define MLX4_MAX_SGE 32
+#define MLX4_MAX_WQE_SIZE \
+	(MLX4_MAX_SGE * sizeof(struct mlx4_wqe_data_seg) + \
+	sizeof(struct mlx4_wqe_ctrl_seg))
 #define MLX4_SEG_SHIFT 4
 
 /* Send queue stamping/invalidating information. */
-- 
1.8.3.1