Re: [dpdk-dev] [PATCH RFC 1/2] net/i40e: allow bulk alloc for the max size desc ring

[Ilya Maximets <i.maximets@samsung.com>]

Ping.

Best regards, Ilya Maximets.

On 19.10.2016 17:07, Ilya Maximets wrote:
> The only reason why bulk alloc disabled for the rings with
> more than (I40E_MAX_RING_DESC - RTE_PMD_I40E_RX_MAX_BURST)
> descriptors is the possible out-of-bound access to the dma
> memory. But it's the artificial limit and can be easily
> avoided by allocating of RTE_PMD_I40E_RX_MAX_BURST more
> descriptors in memory. This will not interfere the HW and,
> as soon as all rings' memory zeroized, Rx functions will
> work correctly.
> 
> This change allows to use vectorized Rx functions with
> 4096 descriptors in Rx ring which is important to achieve
> zero packet drop rate in high-load installations.
> 
> Signed-off-by: Ilya Maximets <i.maximets@samsung.com>
> ---
>  drivers/net/i40e/i40e_rxtx.c | 24 +++++++++++++-----------
>  1 file changed, 13 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/net/i40e/i40e_rxtx.c b/drivers/net/i40e/i40e_rxtx.c
> index 7ae7d9f..1f76691 100644
> --- a/drivers/net/i40e/i40e_rxtx.c
> +++ b/drivers/net/i40e/i40e_rxtx.c
> @@ -409,15 +409,6 @@ check_rx_burst_bulk_alloc_preconditions(__rte_unused struct i40e_rx_queue *rxq)
>  			     "rxq->rx_free_thresh=%d",
>  			     rxq->nb_rx_desc, rxq->rx_free_thresh);
>  		ret = -EINVAL;
> -	} else if (!(rxq->nb_rx_desc < (I40E_MAX_RING_DESC -
> -				RTE_PMD_I40E_RX_MAX_BURST))) {
> -		PMD_INIT_LOG(DEBUG, "Rx Burst Bulk Alloc Preconditions: "
> -			     "rxq->nb_rx_desc=%d, "
> -			     "I40E_MAX_RING_DESC=%d, "
> -			     "RTE_PMD_I40E_RX_MAX_BURST=%d",
> -			     rxq->nb_rx_desc, I40E_MAX_RING_DESC,
> -			     RTE_PMD_I40E_RX_MAX_BURST);
> -		ret = -EINVAL;
>  	}
>  #else
>  	ret = -EINVAL;
> @@ -1698,8 +1689,19 @@ i40e_dev_rx_queue_setup(struct rte_eth_dev *dev,
>  	rxq->rx_deferred_start = rx_conf->rx_deferred_start;
>  
>  	/* Allocate the maximun number of RX ring hardware descriptor. */
> -	ring_size = sizeof(union i40e_rx_desc) * I40E_MAX_RING_DESC;
> -	ring_size = RTE_ALIGN(ring_size, I40E_DMA_MEM_ALIGN);
> +	len = I40E_MAX_RING_DESC;
> +
> +#ifdef RTE_LIBRTE_I40E_RX_ALLOW_BULK_ALLOC
> +	/**
> +	 * Allocating a little more memory because vectorized/bulk_alloc Rx
> +	 * functions doesn't check boundaries each time.
> +	 */
> +	len += RTE_PMD_I40E_RX_MAX_BURST;
> +#endif
> +
> +	ring_size = RTE_ALIGN(len * sizeof(union i40e_rx_desc),
> +			      I40E_DMA_MEM_ALIGN);
> +
>  	rz = rte_eth_dma_zone_reserve(dev, "rx_ring", queue_idx,
>  			      ring_size, I40E_RING_BASE_ALIGN, socket_id);
>  	if (!rz) {
>