> -----Original Message----- > From: Ananyev, Konstantin > Sent: Friday, January 20, 2017 7:25 PM > To: Andrew Rybchenko <arybche...@solarflare.com>; Yang, Zhiyong > <zhiyong.y...@intel.com>; dev@dpdk.org > Cc: thomas.monja...@6wind.com; Richardson, Bruce > <bruce.richard...@intel.com> > Subject: RE: [dpdk-dev] [RFC] lib/librte_ether: consistent PMD batching > behavior > > > > > From: Andrew Rybchenko [mailto:arybche...@solarflare.com] > > Sent: Friday, January 20, 2017 10:26 AM > > To: Yang, Zhiyong <zhiyong.y...@intel.com>; dev@dpdk.org > > Cc: thomas.monja...@6wind.com; Richardson, Bruce > > <bruce.richard...@intel.com>; Ananyev, Konstantin > > <konstantin.anan...@intel.com> > > Subject: Re: [dpdk-dev] [RFC] lib/librte_ether: consistent PMD > > batching behavior > > > > On 01/20/2017 12:51 PM, Zhiyong Yang wrote: > > The rte_eth_tx_burst() function in the file Rte_ethdev.h is invoked to > > transmit output packets on the output queue for DPDK applications as > > follows. > > > > static inline uint16_t > > rte_eth_tx_burst(uint8_t port_id, uint16_t queue_id, > > struct rte_mbuf **tx_pkts, uint16_t nb_pkts); > > > > Note: The fourth parameter nb_pkts: The number of packets to transmit. > > The rte_eth_tx_burst() function returns the number of packets it > > actually sent. The return value equal to *nb_pkts* means that all > > packets have been sent, and this is likely to signify that other > > output packets could be immediately transmitted again. Applications > > that implement a "send as many packets to transmit as possible" policy > > can check this specific case and keep invoking the rte_eth_tx_burst() > > function until a value less than > > *nb_pkts* is returned. > > > > When you call TX only once in rte_eth_tx_burst, you may get different > > behaviors from different PMDs. One problem that every DPDK user has to > > face is that they need to take the policy into consideration at the > > app- lication level when using any specific PMD to send the packets > > whether or not it is necessary, which brings usage complexities and > > makes DPDK users easily confused since they have to learn the details > > on TX function limit of specific PMDs and have to handle the different > > return value: the number of packets transmitted successfully for > > various PMDs. Some PMDs Tx func- tions have a limit of sending at most > > 32 packets for every invoking, some PMDs have another limit of at most > > 64 packets once, another ones have imp- lemented to send as many > > packets to transmit as possible, etc. This will easily cause wrong usage for > DPDK users. > > > > This patch proposes to implement the above policy in DPDK lib in order > > to simplify the application implementation and avoid the incorrect > > invoking as well. So, DPDK Users don't need to consider the > > implementation policy and to write duplicated code at the application > > level again when sending packets. In addition to it, the users don't > > need to know the difference of specific PMD TX and can transmit the > > arbitrary number of packets as they expect when invoking TX API > > rte_eth_tx_burst, then check the return value to get the number of > packets actually sent. > > > > How to implement the policy in DPDK lib? Two solutions are proposed > below. > > > > Solution 1: > > Implement the wrapper functions to remove some limits for each > > specific PMDs as i40e_xmit_pkts_simple and ixgbe_xmit_pkts_simple do > like that. > > > > > IMHO, the solution is a bit better since it: > > > 1. Does not affect other PMDs at all > > > 2. Could be a bit faster for the PMDs which require it since has no > > >indirect > > > function call on each iteration > > > 3. No ABI change > > I also would prefer solution number 1 for the reasons outlined by Andrew > above. > Also, IMO current limitation for number of packets to TX in some Intel PMD > TX routines are sort of artificial: > - they are not caused by any real HW limitations > - avoiding them at PMD level shouldn't cause any performance or functional > degradation. > So I don't see any good reason why instead of fixing these limitations in our > own PMDs we are trying to push them to the upper (rte_ethdev) layer. > > Konstantin
Solution 1 indeed has advantages as Andrew and Konstantin said. Zhiyong
