[dpdk-dev] Regarding rte_eth_rx_burst

[Wang, Haiyue]

> -----Original Message-----
> From: dev <dev-bounces at dpdk.org> On Behalf Of Prashant Upadhyaya
> Sent: Sunday, May 10, 2020 22:06
> To: dev at dpdk.org
> Subject: [dpdk-dev] Regarding rte_eth_rx_burst
> 
> Hi,
> 
> I recently started using X722 NIC which uses i40 PMD of DPDK.
> I am on DPDK 20.02.
> I am seeing that when I call the rte_eth_rx_burst with last argument
> as 1 (polling for 1 mbuf), then I am not receiving data via repeated
> calls.

I saw this kind of issue many times. ;-)

This is *burst* for vector mode:

drivers/net/i40e/i40e_rxtx_vec_sse.c

static inline uint16_t
_recv_raw_pkts_vec(struct i40e_rx_queue *rxq, struct rte_mbuf **rx_pkts,
		   uint16_t nb_pkts, uint8_t *split_packet)
{
      ....

	/* nb_pkts shall be less equal than RTE_I40E_MAX_RX_BURST */
	nb_pkts = RTE_MIN(nb_pkts, RTE_I40E_MAX_RX_BURST);

	/* nb_pkts has to be floor-aligned to RTE_I40E_DESCS_PER_LOOP */
	nb_pkts = RTE_ALIGN_FLOOR(nb_pkts, RTE_I40E_DESCS_PER_LOOP);   <--- nb_pkts = 0, if you passed 1.


> When I go for calls to rte_eth_rx_burst with last argument as 32, the
> function does return the mbuf's as received data.
> 
> Is this expected ? Or this is a bug in the i40 driver handling this NIC ?
> 
> The polls to rte_eth_rx_burst with last argument as 1 works well for
> the ixgbe PMD for sure since I have been using X520 successfully with
> last argument as 1.
> 
> Regards
> -Prashant