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

[Ferruh Yigit <ferruh.yigit@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.

>>
>>>
>>> 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.