net/mlx5e: xsk: Print a warning in slow configurations

On striding RQ, when the XSK frame size doesn't match the MKey page
size, KLM is used for memory mappings, which is a slower mechanism than
MTT or KSM. It may happen in two cases:

1. Frame size is not a power of two (only possible in the unaligned mode
of XSK).

2. Frame size is 2048 bytes, and the firmware doesn't support MKey pages
smaller than 4096 bytes.

Depending on the case, print a warning and recommend to disable striding
RQ or upgrade the firmware.

Signed-off-by: Maxim Mikityanskiy <maximmi@nvidia.com>
Reviewed-by: Tariq Toukan <tariqt@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/mellanox/mlx5/core/en/xsk/pool.c

@@ -99,6 +99,15 @@ static int mlx5e_xsk_enable_locked(struct mlx5e_priv *priv,
 
 	mlx5e_build_xsk_param(pool, &xsk);
 
+	if (priv->channels.params.rq_wq_type == MLX5_WQ_TYPE_LINKED_LIST_STRIDING_RQ &&
+	    mlx5e_mpwrq_umr_mode(priv->mdev, &xsk) == MLX5E_MPWRQ_UMR_MODE_OVERSIZED) {
+		const char *recommendation = is_power_of_2(xsk.chunk_size) ?
+			"Upgrade firmware" : "Disable striding RQ";
+
+		mlx5_core_warn(priv->mdev, "Expected slowdown with XSK frame size %u. %s for better performance.\n",
+			       xsk.chunk_size, recommendation);
+	}
+
 	if (!test_bit(MLX5E_STATE_OPENED, &priv->state)) {
 		/* XSK objects will be created on open. */
 		goto validate_closed;