Re: [dpdk-dev] ixgbe vector rx does not conform torte_eth_rx_burst() API

["Morten Brørup" <mb@smartsharesystems.com>]

> From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Zhao1, Wei
> Sent: Thursday, July 16, 2020 10:50 AM
> 
> Hi,
> 
> > -----Original Message-----
> > From: Morten Brørup <mb@smartsharesystems.com>
> > Sent: Thursday, July 16, 2020 12:03 AM
> > To: Zhao1, Wei <wei.zhao1@intel.com>; Guo, Jia <jia.guo@intel.com>
> > Cc: dev@dpdk.org; Thomas Monjalon <thomas@monjalon.net>; Yigit,
> Ferruh
> > <ferruh.yigit@intel.com>; Andrew Rybchenko
> <arybchenko@solarflare.com>
> > Subject: ixgbe vector rx does not conform to rte_eth_rx_burst() API
> >
> > Wei, Jeff,
> >
> > For the ixgbe driver using vector functions, i.e.
> ixgbe_recv_pkts_vec(), calling
> > rte_eth_rx_burst() with nb_pkts > RTE_IXGBE_MAX_RX_BURST only returns
> > RTE_IXGBE_MAX_RX_BURST packets. E.g. calling rte_eth_rx_burst() with
> > nb_pkts=64 only returns 32 packets.
> >
> >
> > The API description of rte_eth_rx_burst() says:
> >
> > <quote>
> > The rte_eth_rx_burst() function returns the number of packets
> actually
> > retrieved, which is the number of rte_mbuf data structures
> effectively supplied
> > into the rx_pkts array. A return value equal to nb_pkts indicates
> that the RX
> > queue contained at least rx_pkts packets, and this is likely to
> signify that other
> > received packets remain in the input queue. Applications implementing
> a
> > "retrieve as much received packets as possible" policy can check this
> specific
> > case and keep invoking the rte_eth_rx_burst() function until a value
> less than
> > nb_pkts is returned.
> > </quote>
> >
> > The driver implementation does not conform to the documented behavior
> for
> > "retrieve as much received packets as possible" applications.
> 
> It seems not an issue, this function has comment bellow, it is design
> work in that way.
> 
> 
> /*
>  * vPMD receive routine, only accept(nb_pkts >=
> RTE_IXGBE_DESCS_PER_LOOP)
>  *
>  * Notice:
>  * - nb_pkts < RTE_IXGBE_DESCS_PER_LOOP, just return no packet
>  * - nb_pkts > RTE_IXGBE_MAX_RX_BURST, only scan RTE_IXGBE_MAX_RX_BURST
>  *   numbers of DD bit
>  * - floor align nb_pkts to a RTE_IXGBE_DESC_PER_LOOP power-of-two
>  */
> 

I noticed this already. And yes, ixgbe_recv_pkts_vec() does what its comments says.

However, when ixgbe_recv_pkts_vec() is used as the driver's implementation of the rte_eth_rx_burst() function call, the rte_eth_rx_burst() function does not do what is expected of the rte_eth_rx_burst() function.

The implementation must conform to the API that it implements.

If you don't want to update the ixgbe_recv_pkts_vec() function, I propose that you add a wrapper function that calls ixgbe_recv_pkts_vec() repeatedly, and use the wrapper function as the implementation of the rte_eth_rx_burst() function.