Re: [dpdk-dev] [PATCH v1] ixgbe: remove vector pmd burst size restriction

["Liang, Cunming" <cunming.liang@intel.com>]

Hi, 

[...]
> > diff --git a/drivers/net/ixgbe/ixgbe_rxtx.c b/drivers/net/ixgbe/ixgbe_rxtx.c
> > index 3f808b3..dbdb761 100644
> > --- a/drivers/net/ixgbe/ixgbe_rxtx.c
> > +++ b/drivers/net/ixgbe/ixgbe_rxtx.c
> > @@ -4008,7 +4008,8 @@ ixgbe_set_rx_function(struct rte_eth_dev *dev)
> >   	 */
> >   	} else if (adapter->rx_vec_allowed) {
> >   		PMD_INIT_LOG(DEBUG, "Vector rx enabled, please make sure
> RX "
> > -				   "burst size no less than 32.");
> > +				    "burst size no less than 4 (port=%d).",
> > +			     dev->data->port_id);
> 
> I think it would be better to use RTE_IXGBE_DESCS_PER_LOOP instead of a
> constant 4.
> >
[...]
> >
> >   /*
> > - * vPMD receive routine, now only accept (nb_pkts ==
> RTE_IXGBE_VPMD_RX_BURST)
> > - * in one loop
> > + * vPMD raw receive routine
> I would keep some warning there, like "(if nb_pkts <
> RTE_IXGBE_DESCS_PER_LOOP, won't receive anything)"
> 
> >    *
> >    * Notice:
> > - * - nb_pkts < RTE_IXGBE_VPMD_RX_BURST, just return no packet
> > - * - nb_pkts > RTE_IXGBE_VPMD_RX_BURST, only scan
> RTE_IXGBE_VPMD_RX_BURST
> > - *   numbers of DD bit
> > + * - floor align nb_pkts to a RTE_IXGBE_DESC_PER_LOOP power-of-two
> > + * - 'nb_pkts < 4' causes 0 packet receiving
> Again, RTE_IXGBE_DESCS_PER_LOOP would be better than 4
> 
[...]
> >   uint16_t
> >   ixgbe_recv_scattered_pkts_vec(void *rx_queue, struct rte_mbuf **rx_pkts,
> >   		uint16_t nb_pkts)
> >   {
> >   	struct ixgbe_rx_queue *rxq = rx_queue;
> > -	uint8_t split_flags[RTE_IXGBE_VPMD_RX_BURST] = {0};
> > +	uint8_t split_flags[nb_pkts];
> > +
> > +	memset(split_flags, 0, nb_pkts);
> >
> >   	/* get some new buffers */
> >   	uint16_t nb_bufs = _recv_raw_pkts_vec(rxq, rx_pkts, nb_pkts,
> 
> After this _recv_raw_pkts_vec it checks 32 bytes in split_flags (4x8
> bytes), that can overrun or miss some flags.
> Btw. Bruce just fixed that part in "ixgbe: fix check for split packets"
> 
> 
Thanks for all these valuable comments, will keep the max burst size 32.