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

["Morten Brørup" <mb@smartsharesystems.com>]

> 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.

> 
> 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.