Re: [PATCH] net/mlx4: verify Tx max sges

[Adrien Mazarguil <adrien.mazarguil@6wind.com>]

On Thu, Jan 04, 2018 at 06:12:03PM +0200, Moti Haimovsky wrote:
> 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>

Except for a really minor nit below:

Acked-by: Adrien Mazarguil <adrien.mazarguil@6wind.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))

One extra indent space is needed before sizeof to align with parenthesis
contents.

-- 
Adrien Mazarguil
6WIND