Re: [dpdk-dev] [PATCH v4] net/i40e: fix Rx instability with vector mode

["Ananyev, Konstantin" <konstantin.ananyev@intel.com>]

> 
> Previously, there is instability during vector Rx if descriptor
> number is not power of 2, e.g. process hang and some Rx packets
> are unexpectedly empty. That's because vector Rx mode assumes Rx
> descriptor number is power of 2 when doing bit mask.
> This patch allows vector mode only when the number of Rx descriptor
> is power of 2.
> 
> Fixes: 8e109464c022 ("i40e: allow vector Rx and Tx usage")
> Fixes: a3c83a2527e1 ("net/i40e: enable runtime queue setup")
> Cc: stable@dpdk.org
> 
> Signed-off-by: Beilei Xing <beilei.xing@intel.com>
> ---
> v4 changes:
>  - Configure rx_vec_allowed in i40e_rx_vec_dev_conf_condition_check function.
> v3 changes:
>  - Add branch for non-first queue during runtime queue setup.
>  - Use function rte_is_power_of_2().
>  - Configure rx_vec_allowed during setting Rx function.
> v2 changes:
>  - rx_vec_allowed is global configuration, avoid overwrite.
> 
>  doc/guides/nics/i40e.rst                |  7 ++++++
>  drivers/net/i40e/i40e_rxtx.c            |  5 +++++
>  drivers/net/i40e/i40e_rxtx_vec_common.h | 38 +++++++++++++++++++++++++++++++++
>  3 files changed, 50 insertions(+)
> 
> diff --git a/doc/guides/nics/i40e.rst b/doc/guides/nics/i40e.rst
> index ab3928a..bfacbd1 100644
> --- a/doc/guides/nics/i40e.rst
> +++ b/doc/guides/nics/i40e.rst
> @@ -172,6 +172,13 @@ Runtime Config Options
> 
>    -w 84:00.0,use-latest-supported-vec=1
> 
> +Vector RX Pre-conditions
> +~~~~~~~~~~~~~~~~~~~~~~~~
> +For Vector RX it is assumed that the number of descriptor rings will be a power
> +of 2. With this pre-condition, the ring pointer can easily scroll back to the
> +head after hitting the tail without a conditional check. In addition Vector RX
> +can use this assumption to do a bit mask using ``ring_size - 1``.
> +
>  Driver compilation and testing
>  ------------------------------
> 
> diff --git a/drivers/net/i40e/i40e_rxtx.c b/drivers/net/i40e/i40e_rxtx.c
> index a827456..5bb1a3c 100644
> --- a/drivers/net/i40e/i40e_rxtx.c
> +++ b/drivers/net/i40e/i40e_rxtx.c
> @@ -1741,6 +1741,11 @@ i40e_dev_rx_queue_setup_runtime(struct rte_eth_dev *dev,
>  			ad->rx_bulk_alloc_allowed = false;
>  		i40e_set_rx_function(dev);
>  		return 0;
> +	} else if (ad->rx_vec_allowed && !rte_is_power_of_2(rxq->nb_rx_desc)) {
> +		PMD_DRV_LOG(ERR, "Vector mode is allowed, but descriptor"
> +			    " number %d of queue %d isn't power of 2",
> +			    rxq->nb_rx_desc, rxq->queue_id);
> +		return -EINVAL;
>  	}
> 
>  	/* check bulk alloc conflict */
> diff --git a/drivers/net/i40e/i40e_rxtx_vec_common.h b/drivers/net/i40e/i40e_rxtx_vec_common.h
> index f00f6d6..0e6ffa0 100644
> --- a/drivers/net/i40e/i40e_rxtx_vec_common.h
> +++ b/drivers/net/i40e/i40e_rxtx_vec_common.h
> @@ -192,8 +192,13 @@ static inline int
>  i40e_rx_vec_dev_conf_condition_check_default(struct rte_eth_dev *dev)
>  {
>  #ifndef RTE_LIBRTE_IEEE1588
> +	struct i40e_adapter *ad =
> +		I40E_DEV_PRIVATE_TO_ADAPTER(dev->data->dev_private);
>  	struct rte_eth_rxmode *rxmode = &dev->data->dev_conf.rxmode;
>  	struct rte_fdir_conf *fconf = &dev->data->dev_conf.fdir_conf;
> +	struct i40e_rx_queue *rxq;
> +	uint16_t desc, i;
> +	bool first_queue;
> 
>  	/* no fdir support */
>  	if (fconf->mode != RTE_FDIR_MODE_NONE)
> @@ -207,6 +212,39 @@ i40e_rx_vec_dev_conf_condition_check_default(struct rte_eth_dev *dev)
>  	if (rxmode->offloads & DEV_RX_OFFLOAD_VLAN_EXTEND)
>  		return -1;
> 
> +	/**
> +	 * Vector mode is allowed only when number of Rx queue
> +	 * descriptor is power of 2.
> +	 */
> +	if (!dev->data->dev_started) {
> +		first_queue = true;
> +		for (i = 0; i < dev->data->nb_rx_queues; i++) {
> +			rxq = dev->data->rx_queues[i];
> +			if (!rxq)
> +				continue;
> +			desc = rxq->nb_rx_desc;
> +			if (first_queue)
> +				ad->rx_vec_allowed =
> +					rte_is_power_of_2(desc);
> +			else
> +				ad->rx_vec_allowed =
> +					ad->rx_vec_allowed ?
> +					rte_is_power_of_2(desc) :
> +					ad->rx_vec_allowed;
> +			first_queue = false;
> +		}
> +	} else {
> +		/* Only check the first queue's descriptor number */
> +		for (i = 0; i < dev->data->nb_rx_queues; i++) {
> +			rxq = dev->data->rx_queues[i];
> +			if (!rxq)
> +				continue;
> +			desc = rxq->nb_rx_desc;
> +			ad->rx_vec_allowed = rte_is_power_of_2(desc);
> +			break;
> +		}
> +	}
> +
>  	return 0;
>  #else
>  	RTE_SET_USED(dev);
> --

Acked-by: Konstantin Ananyev <konstantin.ananyev@intel.com>

> 2.5.5