Re: [dpdk-dev] [PATCH] net/mlx5: fix Tx doorbell memory barrier

["Nélio Laranjeiro" <nelio.laranjeiro@6wind.com>]

On Sun, Oct 22, 2017 at 01:00:22AM -0700, Yongseok Koh wrote:
>[...]
> --- a/drivers/net/mlx5/mlx5_rxtx.h
> +++ b/drivers/net/mlx5/mlx5_rxtx.h
> @@ -584,9 +584,11 @@ mlx5_tx_mb2mr(struct mlx5_txq_data *txq, struct rte_mbuf *mb)
>   *   Pointer to TX queue structure.
>   * @param wqe
>   *   Pointer to the last WQE posted in the NIC.
> + * @param mb
> + *   Request for write memory barrier after BF update.

BF should be replaced by its real name i.e. BlueFlame.
If the mb is only related to the BlueFlame, why not naming it mbbf or
bfmf?

>   */
>  static __rte_always_inline void
> -mlx5_tx_dbrec(struct mlx5_txq_data *txq, volatile struct mlx5_wqe *wqe)
> +mlx5_tx_dbrec(struct mlx5_txq_data *txq, volatile struct mlx5_wqe *wqe, int mb)
>  {
>  	uint64_t *dst = (uint64_t *)((uintptr_t)txq->bf_reg);
>  	volatile uint64_t *src = ((volatile uint64_t *)wqe);
> @@ -596,6 +598,8 @@ mlx5_tx_dbrec(struct mlx5_txq_data *txq, volatile struct mlx5_wqe *wqe)
>  	/* Ensure ordering between DB record and BF copy. */
>  	rte_wmb();
>  	*dst = *src;
> +	if (mb)
> +		rte_wmb();
>  }

My last point, this modification seems necessary only for the MPS vector
case, why not adding a new function for this specific case instead?

At least I would suggest to create an enum with the possible values it
helps to read the source:

 enum mlx5_blueflame_mb {
 	MLX5_BLUEFLAME_MB_DIS, 
 	MLX5_BLUEFLAME_MB_EN, 
 }

you can also create wrappers for the function to avoid this extract
argument in the tx code:

 mlx5_tx_dbrec_bfmb(txq, wqe);
 mlx5_tx_dbrec_no_bfmb(txq, wqe);

Multiple ways instead of having 0 or 1 hard coded.

Thanks,

-- 
Nélio Laranjeiro
6WIND