Re: [dpdk-dev] [PATCH] parray: introduce internal API for dynamic arrays

["Ananyev, Konstantin" <konstantin.ananyev@intel.com>]

> 
> On 6/21/2021 1:30 PM, Ananyev, Konstantin wrote:
> >
> >>
> >>> From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Ananyev,
> >>> Konstantin
> >>>
> >>>>> How can we hide the callbacks since they are used by inline burst
> >>> functions.
> >>>>
> >>>> I probably I owe a better explanation to what I meant in first mail.
> >>>> Otherwise it sounds confusing.
> >>>> I'll try to write a more detailed one in next few days.
> >>>
> >>> Actually I gave it another thought over weekend, and might be we can
> >>> hide rte_eth_dev_cb even in a simpler way. I'd use eth_rx_burst() as
> >>> an example, but the same principle applies to other 'fast' functions.
> >>>
> >>>  1. Needed changes for PMDs rx_pkt_burst():
> >>>     a) change function prototype to accept 'uint16_t port_id' and
> >>> 'uint16_t queue_id',
> >>>          instead of current 'void *'.
> >>>     b) Each PMD rx_pkt_burst() will have to call rte_eth_rx_epilog()
> >>> function at return.
> >>>          This  inline function will do all CB calls for that queue.
> >>>
> >>> To be more specific, let say we have some PMD: xyz with RX function:
> >>>
> >>> uint16_t
> >>> xyz_recv_pkts(void *rx_queue, struct rte_mbuf **rx_pkts, uint16_t
> >>> nb_pkts)
> >>> {
> >>>      struct xyz_rx_queue *rxq = rx_queue;
> >>>      uint16_t nb_rx = 0;
> >>>
> >>>      /* do actual stuff here */
> >>>     ....
> >>>     return nb_rx;
> >>> }
> >>>
> >>> It will be transformed to:
> >>>
> >>> uint16_t
> >>> xyz_recv_pkts(uint16_t port_id, uint16_t queue_id, struct rte_mbuf
> >>> **rx_pkts, uint16_t nb_pkts)
> >>> {
> >>>          struct xyz_rx_queue *rxq;
> >>>          uint16_t nb_rx;
> >>>
> >>>          rxq = _rte_eth_rx_prolog(port_id, queue_id);
> >>>          if (rxq == NULL)
> >>>              return 0;
> >>>          nb_rx = _xyz_real_recv_pkts(rxq, rx_pkts, nb_pkts);
> >>>          return _rte_eth_rx_epilog(port_id, queue_id, rx_pkts,
> >>> nb_pkts);
> >>> }
> >>>
> >>> And somewhere in ethdev_private.h:
> >>>
> >>> static inline void *
> >>> _rte_eth_rx_prolog(uint16_t port_id, uint16_t queue_id);
> >>> {
> >>>    struct rte_eth_dev *dev = &rte_eth_devices[port_id];
> >>>
> >>> #ifdef RTE_ETHDEV_DEBUG_RX
> >>>         RTE_ETH_VALID_PORTID_OR_ERR_RET(port_id, NULL);
> >>>         RTE_FUNC_PTR_OR_ERR_RET(*dev->rx_pkt_burst, NULL);
> >>>
> >>>         if (queue_id >= dev->data->nb_rx_queues) {
> >>>                 RTE_ETHDEV_LOG(ERR, "Invalid RX queue_id=%u\n",
> >>> queue_id);
> >>>                 return NULL;
> >>>         }
> >>> #endif
> >>>   return dev->data->rx_queues[queue_id];
> >>> }
> >>>
> >>> static inline uint16_t
> >>> _rte_eth_rx_epilog(uint16_t port_id, uint16_t queue_id, struct rte_mbuf
> >>> **rx_pkts, const uint16_t nb_pkts);
> >>> {
> >>>     struct rte_eth_dev *dev = &rte_eth_devices[port_id];
> >>>
> >>> #ifdef RTE_ETHDEV_RXTX_CALLBACKS
> >>>         struct rte_eth_rxtx_callback *cb;
> >>>
> >>>         /* __ATOMIC_RELEASE memory order was used when the
> >>>          * call back was inserted into the list.
> >>>          * Since there is a clear dependency between loading
> >>>          * cb and cb->fn/cb->next, __ATOMIC_ACQUIRE memory order is
> >>>          * not required.
> >>>          */
> >>>         cb = __atomic_load_n(&dev->post_rx_burst_cbs[queue_id],
> >>>                                 __ATOMIC_RELAXED);
> >>>
> >>>         if (unlikely(cb != NULL)) {
> >>>                 do {
> >>>                         nb_rx = cb->fn.rx(port_id, queue_id, rx_pkts,
> >>> nb_rx,
> >>>                                                 nb_pkts, cb->param);
> >>>                         cb = cb->next;
> >>>                 } while (cb != NULL);
> >>>         }
> >>> #endif
> >>>
> >>>         rte_ethdev_trace_rx_burst(port_id, queue_id, (void **)rx_pkts,
> >>> nb_rx);
> >>>         return nb_rx;
> >>>  }
> >>
> >> That would make the compiler inline _rte_eth_rx_epilog() into the driver when compiling the DPDK library. But
> >> RTE_ETHDEV_RXTX_CALLBACKS is a definition for the application developer to use when compiling the DPDK application.
> >
> > I believe it is for both - user app and DPDK drivers.
> > AFAIK, they both have to use the same rte_config.h, otherwise things will be broken.
> > If let say RTE_ETHDEV_RXTX_CALLBACKS is not enabled in ethdev, then
> > user wouldn't be able to add a callback at first place.
> > BTW,  such change will allow us to make RTE_ETHDEV_RXTX_CALLBACKS
> > internal for ethdev/PMD layer, which is a good thing from my perspective.
> >
> 
> It is possible to use binary drivers (.so) as plugin. Currently application can
> decide to use or not use Rx/Tx callbacks even with binary drivers, but this
> change adds a complexity to this usecase.

Not sure I understand you here...
Can you explain a bit more what do you mean?

> 
> >>
> >>>
> >>> Now, as you said above, in rte_ethdev.h we will keep only a flat array
> >>> with pointers to 'fast' functions:
> >>> struct {
> >>>      eth_rx_burst_t             rx_pkt_burst
> >>>       eth_tx_burst_t             tx_pkt_burst;
> >>>       eth_tx_prep_t              tx_pkt_prepare;
> >>>      .....
> >>> } rte_eth_dev_burst[];
> >>>
> >>> And rte_eth_rx_burst() will look like:
> >>>
> >>> static inline uint16_t
> >>> rte_eth_rx_burst(uint16_t port_id, uint16_t queue_id,
> >>>                  struct rte_mbuf **rx_pkts, const uint16_t nb_pkts)
> >>> {
> >>>     if (port_id >= RTE_MAX_ETHPORTS)
> >>>         return 0;
> >>>    return rte_eth_dev_burst[port_id](port_id, queue_id, rx_pkts,
> >>> nb_pkts);
> >>> }
> >>>
> >>> Yes, it will require changes in *all* PMDs, but as I said before the
> >>> changes will be a mechanic ones.