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

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

> -----Original Message-----
> From: Wang, Haiyue
> Sent: Tuesday, September 28, 2021 11:06
> To: 'Julien Meunier' <julien.meunier@nokia.com>; dev@dpdk.org
> Cc: stable@dpdk.org; Richardson, Bruce <bruce.richardson@intel.com>
> Subject: RE: [PATCH] net/ixgbe: fix RxQ/TxQ release
> 
> > -----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 ?
> 

My fault, yes, possible. ;-)

> 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;
> >

Just one line ?

i = (i + 1) % txq->nb_tx_desc

> >  	/* 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