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

["Zhao1, Wei" <wei.zhao1@intel.com>]

HI, 

> -----Original Message-----
> From: Morten Brørup <mb@smartsharesystems.com>
> Sent: Thursday, July 16, 2020 5:09 PM
> 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: RE: [dpdk-dev] ixgbe vector rx does not conform torte_eth_rx_burst()
> API
> 
> > 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.

Get your point, I know what you need, but is there any risk for ixgbe_recv_pkts_vec? I am not sure.
Maybe you can have a try first, if it work well, you can submit a patch.
What you need is this:

uint16_t
i40e_recv_scattered_pkts_vec_avx2(void *rx_queue, struct rte_mbuf **rx_pkts,
			     uint16_t nb_pkts)
{
	uint16_t retval = 0;
	while (nb_pkts > RTE_I40E_VPMD_RX_BURST) {
		uint16_t burst = i40e_recv_scattered_burst_vec_avx2(rx_queue,
				rx_pkts + retval, RTE_I40E_VPMD_RX_BURST);
		retval += burst;
		nb_pkts -= burst;
		if (burst < RTE_I40E_VPMD_RX_BURST)
			return retval;
	}
	return retval + i40e_recv_scattered_burst_vec_avx2(rx_queue,
				rx_pkts + retval, nb_pkts);
}