Re: [dpdk-dev] [PATCH v3] net/i40e: fix Rx instability with vector mode

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

Hi

> 
> 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>
> ---
> 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 | 30 +++++++++++++++++++++++++++---
>  2 files changed, 34 insertions(+), 3 deletions(-)
> 
> 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..771193a 100644
> --- a/drivers/net/i40e/i40e_rxtx.c
> +++ b/drivers/net/i40e/i40e_rxtx.c
> @@ -1735,12 +1735,21 @@ i40e_dev_rx_queue_setup_runtime(struct rte_eth_dev *dev,
>  		 * i40e_set_rx_function.
>  		 */
>  		ad->rx_bulk_alloc_allowed = true;
> -		ad->rx_vec_allowed = true;
>  		dev->data->scattered_rx = use_scattered_rx;
>  		if (use_def_burst_func)
>  			ad->rx_bulk_alloc_allowed = false;
> +		/**
> +		 * Vector mode is allowed only when number of Rx queue
> +		 * descriptor is a power of 2.
> +		 */
> +		ad->rx_vec_allowed = rte_is_power_of_2(rxq->nb_rx_desc);

Actually do we need to do it here?
We call set_rx_function() anyway, it would do that check for us, wouldn't it?

>  		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 */
> @@ -2948,11 +2957,26 @@ i40e_set_rx_function(struct rte_eth_dev *dev)
>  {
>  	struct i40e_adapter *ad =
>  		I40E_DEV_PRIVATE_TO_ADAPTER(dev->data->dev_private);
> +	struct i40e_rx_queue *rxq;
>  	uint16_t rx_using_sse, i;
> +	uint16_t desc;

Please add empty line between var definitions and start of code.
Helps readability.

>  	/* In order to allow Vector Rx there are a few configuration
>  	 * conditions to be met and Rx Bulk Allocation should be allowed.
>  	 */
>  	if (rte_eal_process_type() == RTE_PROC_PRIMARY) {
> +		if (!dev->data->dev_started) {
> +			for (i = 0; i < dev->data->nb_rx_queues; i++) {
> +				rxq = dev->data->rx_queues[i];
> +				desc = rxq->nb_rx_desc;
> +				if (!i)
> +					ad->rx_vec_allowed =
> +						rte_is_power_of_2(desc);
> +				else if (ad->rx_vec_allowed &&
> +					 !rte_is_power_of_2(desc))
> +					ad->rx_vec_allowed = false;

Wouldn't be a bit cleaner:
ad->rx_vec_allowed = (ad->rx_vec_allowed == true) ? rte_is_power_of_2(desc)) : ad->rx_vec_allowed;

> +			}
> +		}
> +

Probably better to move that code into i40e_rx_vec_dev_conf_condition_check()
that will be called on next line?

>  		if (i40e_rx_vec_dev_conf_condition_check(dev) ||
>  		    !ad->rx_bulk_alloc_allowed) {
>  			PMD_INIT_LOG(DEBUG, "Port[%d] doesn't meet"
> @@ -2961,10 +2985,10 @@ i40e_set_rx_function(struct rte_eth_dev *dev)
> 
>  			ad->rx_vec_allowed = false;
>  		}
> +
>  		if (ad->rx_vec_allowed) {
>  			for (i = 0; i < dev->data->nb_rx_queues; i++) {
> -				struct i40e_rx_queue *rxq =
> -					dev->data->rx_queues[i];
> +				rxq = dev->data->rx_queues[i];
> 
>  				if (rxq && i40e_rxq_vec_setup(rxq)) {
>  					ad->rx_vec_allowed = false;
> --
> 2.5.5