Re: [dpdk-dev] [PATCH] net/ixgbe: fix RxQ/TxQ release

["Wang, Haiyue" <haiyue.wang@intel.com>]

> -----Original Message-----
> From: Julien Meunier <julien.meunier@nokia.com>
> Sent: Tuesday, September 28, 2021 01:18
> To: dev@dpdk.org
> Cc: stable@dpdk.org; Richardson, Bruce <bruce.richardson@intel.com>; Wang, Haiyue
> <haiyue.wang@intel.com>
> Subject: [PATCH] net/ixgbe: fix RxQ/TxQ release
> 
> On the vector implementation, during the tear-down, the mbufs not
> drained in the RxQ and TxQ are freed based on an algorithm which
> supposed that the number of descriptors is a power of 2 (max_desc).
> Based on this hypothesis, this algorithm uses a bitmask in order to
> detect an index overflow during the iteration, and to restart the loop
> from 0.
> 
> However, there is no such power of 2 requirement in the ixgbe for the
> number of descriptors in the RxQ / TxQ. The only requirement is to have
> a number correctly aligned.
> 
> If a user requested to configure a number of descriptors which is not a
> power of 2, as a consequence, during the tear-down, it was possible to
> be in an infinite loop, and to never reach the exit loop condition.
> 

Are you able to setup not a power of 2 successfully ?

int
rte_eth_tx_queue_setup(uint16_t port_id, uint16_t tx_queue_id,
		       uint16_t nb_tx_desc, unsigned int socket_id,
		       const struct rte_eth_txconf *tx_conf)
{
	...

	if (nb_tx_desc > dev_info.tx_desc_lim.nb_max ||
	    nb_tx_desc < dev_info.tx_desc_lim.nb_min ||
	    nb_tx_desc % dev_info.tx_desc_lim.nb_align != 0) {
		RTE_ETHDEV_LOG(ERR,
			"Invalid value for nb_tx_desc(=%hu), should be: <= %hu, >= %hu, and a product of %hu\n",
			nb_tx_desc, dev_info.tx_desc_lim.nb_max,
			dev_info.tx_desc_lim.nb_min,
			dev_info.tx_desc_lim.nb_align);
		return -EINVAL;
	}

	...

}

> By removing the bitmask and changing the loop method, we can avoid this
> issue, and allow the user to configure a RxQ / TxQ which is not a power
> of 2.
> 
> Fixes: c95584dc2b18 ("ixgbe: new vectorized functions for Rx/Tx")
> Cc: bruce.richardson@intel.com
> Cc: stable@dpdk.org
> 
> Signed-off-by: Julien Meunier <julien.meunier@nokia.com>
> ---
>  drivers/net/ixgbe/ixgbe_rxtx_vec_common.h | 20 +++++++++++++-------
>  1 file changed, 13 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/net/ixgbe/ixgbe_rxtx_vec_common.h b/drivers/net/ixgbe/ixgbe_rxtx_vec_common.h
> index adba855ca3..8912558918 100644
> --- a/drivers/net/ixgbe/ixgbe_rxtx_vec_common.h
> +++ b/drivers/net/ixgbe/ixgbe_rxtx_vec_common.h
> @@ -150,11 +150,14 @@ _ixgbe_tx_queue_release_mbufs_vec(struct ixgbe_tx_queue *txq)
>  		return;
> 
>  	/* release the used mbufs in sw_ring */
> -	for (i = txq->tx_next_dd - (txq->tx_rs_thresh - 1);
> -	     i != txq->tx_tail;
> -	     i = (i + 1) & max_desc) {
> +	i = txq->tx_next_dd - (txq->tx_rs_thresh - 1);
> +	while (i != txq->tx_tail) {
>  		txe = &txq->sw_ring_v[i];
>  		rte_pktmbuf_free_seg(txe->mbuf);
> +
> +		i = i + 1;
> +		if (i > max_desc)
> +			i = 0;
>  	}
>  	txq->nb_tx_free = max_desc;
> 
> @@ -168,7 +171,7 @@ _ixgbe_tx_queue_release_mbufs_vec(struct ixgbe_tx_queue *txq)
>  static inline void
>  _ixgbe_rx_queue_release_mbufs_vec(struct ixgbe_rx_queue *rxq)
>  {
> -	const unsigned int mask = rxq->nb_rx_desc - 1;
> +	const unsigned int max_desc = rxq->nb_rx_desc - 1;
>  	unsigned int i;
> 
>  	if (rxq->sw_ring == NULL || rxq->rxrearm_nb >= rxq->nb_rx_desc)
> @@ -181,11 +184,14 @@ _ixgbe_rx_queue_release_mbufs_vec(struct ixgbe_rx_queue *rxq)
>  				rte_pktmbuf_free_seg(rxq->sw_ring[i].mbuf);
>  		}
>  	} else {
> -		for (i = rxq->rx_tail;
> -		     i != rxq->rxrearm_start;
> -		     i = (i + 1) & mask) {
> +		i = rxq->rx_tail;
> +		while (i != rxq->rxrearm_start) {
>  			if (rxq->sw_ring[i].mbuf != NULL)
>  				rte_pktmbuf_free_seg(rxq->sw_ring[i].mbuf);
> +
> +			i = i + 1;
> +			if (i > max_desc)
> +				i = 0;
>  		}
>  	}
> 
> --
> 2.17.1