[dpdk-dev] Regarding rte_eth_rx_burst

[Prashant Upadhyaya]

Thanks Wang !
...which begs the proverbial question -- is this a bug or a feature ?
I would say it is a bug as the polling for 1 mbuf works for the other
PMD's, worse still the setting to zero is done in a quiet manner
leading to entire rx blockage if the caller keeps calling with polling
for 1 mbuf and keeps wondering why the rx is not working.

Regards
-Prashant


On Sun, May 10, 2020 at 10:46 PM Wang, Haiyue <haiyue.wang at intel.com> wrote:
>
> > -----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