On Thu, Jul 16, 2020 at 11:08:49AM +0200, Morten Brørup wrote: > > From: dev [mailto:dev-boun...@dpdk.org] On Behalf Of Zhao1, Wei > > Sent: Thursday, July 16, 2020 10:50 AM > > > > Hi, > > > > > -----Original Message----- > > > From: Morten Brørup <m...@smartsharesystems.com> > > > Sent: Thursday, July 16, 2020 12:03 AM > > > To: Zhao1, Wei <wei.zh...@intel.com>; Guo, Jia <jia....@intel.com> > > > Cc: dev@dpdk.org; Thomas Monjalon <tho...@monjalon.net>; Yigit, > > Ferruh > > > <ferruh.yi...@intel.com>; Andrew Rybchenko > > <arybche...@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. > I agree it does not conform to the API as documented. Looking at the i40e AVX2 vector code paths, the regular (no-fragmented packets) path does not seem to put a limit on the size of burst received, while the scattered receive path uses the latter scheme of a wrapper function. Therefore, either approach should work for ixgbe driver, I think.
/Bruce
