[dpdk-dev] ixgbe vector rx does not conform to rte_eth_rx_burst() API

[Zhao1, Wei]

Hi, 

> -----Original Message-----
> From: Morten Brørup <mb at smartsharesystems.com>
> Sent: Thursday, July 16, 2020 12:03 AM
> To: Zhao1, Wei <wei.zhao1 at intel.com>; Guo, Jia <jia.guo at intel.com>
> Cc: dev at dpdk.org; Thomas Monjalon <thomas at monjalon.net>; Yigit, Ferruh
> <ferruh.yigit at intel.com>; Andrew Rybchenko <arybchenko at 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
 */

> 
> 
> Med venlig hilsen / kind regards
> - Morten Brørup