RE: [PATCH v6 1/4] ethdev: add API for mbufs recycle mode

[Feifei Wang <Feifei.Wang2@arm.com>]

[...]
> > Probably I am missing something, but why it is not possible to do something
> like that:
> >
> > rte_eth_recycle_mbufs(rx_port_id=X, rx_queue_id=Y, tx_port_id=N,
> > tx_queue_id=M, ...); ....
> > rte_eth_recycle_mbufs(rx_port_id=X, rx_queue_id=Y, tx_port_id=N,
> > tx_queue_id=K, ...);
> >
> > I.E. feed rx queue from 2 tx queues?
> >
> > Two problems for this:
> > 1. If we have 2 tx queues for rx, the thread should make the extra
> > judgement to decide which one to choose in the driver layer.
> 
> Not sure, why on the driver layer?
> The example I gave above - decision is made on application layer.
> Lets say first call didn't free enough mbufs, so app decided to use second txq
> for rearm.
[Feifei] I think currently mbuf recycle mode can support this usage. For examples:
n =  rte_eth_recycle_mbufs(rx_port_id=X, rx_queue_id=Y, tx_port_id=N, tx_queue_id=M, ...);
if (n < planned_number)
rte_eth_recycle_mbufs(rx_port_id=X, rx_queue_id=Y, tx_port_id=N, tx_queue_id=K, ...);

Thus, if users want, they can do like this. 

> 
> > On the other hand, current mechanism can support users to switch 1 txq
> > to another timely in the application layer. If user want to choose
> > another txq, he just need to change the txq_queue_id parameter in the API.
> > 2. If you want one rxq to support two txq at the same time, this needs
> > to add spinlock on guard variable to avoid multi-thread conflict.
> > Spinlock will decrease the data-path performance greatly.  Thus, we do
> > not consider
> > 1 rxq mapping multiple txqs here.
> 
> I am talking about situation when one thread controls 2 tx queues.
> 
> > + *
> > + * @param rx_port_id
> > + * Port identifying the receive side.
> > + * @param rx_queue_id
> > + * The index of the receive queue identifying the receive side.
> > + * The value must be in the range [0, nb_rx_queue - 1] previously
> > +supplied
> > + * to rte_eth_dev_configure().
> > + * @param tx_port_id
> > + * Port identifying the transmit side.
> > + * @param tx_queue_id
> > + * The index of the transmit queue identifying the transmit side.
> > + * The value must be in the range [0, nb_tx_queue - 1] previously
> > +supplied
> > + * to rte_eth_dev_configure().
> > + * @param recycle_rxq_info
> > + * A pointer to a structure of type *rte_eth_recycle_rxq_info* which
> > +contains
> > + * the information of the Rx queue mbuf ring.
> > + * @return
> > + * The number of recycling mbufs.
> > + */
> > +__rte_experimental
> > +static inline uint16_t
> > +rte_eth_recycle_mbufs(uint16_t rx_port_id, uint16_t rx_queue_id,
> > +uint16_t tx_port_id, uint16_t tx_queue_id,  struct
> > +rte_eth_recycle_rxq_info *recycle_rxq_info) {  struct rte_eth_fp_ops
> > +*p;  void *qd;  uint16_t nb_mbufs;
> > +
> > +#ifdef RTE_ETHDEV_DEBUG_TX
> > + if (tx_port_id >= RTE_MAX_ETHPORTS ||  tx_queue_id >=
> > +RTE_MAX_QUEUES_PER_PORT) {  RTE_ETHDEV_LOG(ERR,  "Invalid
> > +tx_port_id=%u or tx_queue_id=%u\n",  tx_port_id, tx_queue_id);
> > +return 0;  } #endif
> > +
> > + /* fetch pointer to queue data */
> > + p = &rte_eth_fp_ops[tx_port_id];
> > + qd = p->txq.data[tx_queue_id];
> > +
> > +#ifdef RTE_ETHDEV_DEBUG_TX
> > + RTE_ETH_VALID_PORTID_OR_ERR_RET(tx_port_id, 0);
> > +
> > + if (qd == NULL) {
> > + RTE_ETHDEV_LOG(ERR, "Invalid Tx queue_id=%u for port_id=%u\n",
> > +tx_queue_id, tx_port_id);  return 0;  } #endif  if
> > +(p->recycle_tx_mbufs_reuse == NULL)  return 0;
> > +
> > + /* Copy used *rte_mbuf* buffer pointers from Tx mbuf ring
> > + * into Rx mbuf ring.
> > + */
> > + nb_mbufs = p->recycle_tx_mbufs_reuse(qd, recycle_rxq_info);
> > +
> > + /* If no recycling mbufs, return 0. */ if (nb_mbufs == 0) return 0;
> > +
> > +#ifdef RTE_ETHDEV_DEBUG_RX
> > + if (rx_port_id >= RTE_MAX_ETHPORTS ||  rx_queue_id >=
> > +RTE_MAX_QUEUES_PER_PORT) {  RTE_ETHDEV_LOG(ERR, "Invalid
> > +rx_port_id=%u or rx_queue_id=%u\n",  rx_port_id, rx_queue_id);
> > +return 0;  } #endif
> > +
> > + /* fetch pointer to queue data */
> > + p = &rte_eth_fp_ops[rx_port_id];
> > + qd = p->rxq.data[rx_queue_id];
> > +
> > +#ifdef RTE_ETHDEV_DEBUG_RX
> > + RTE_ETH_VALID_PORTID_OR_ERR_RET(rx_port_id, 0);
> > +
> > + if (qd == NULL) {
> > + RTE_ETHDEV_LOG(ERR, "Invalid Rx queue_id=%u for port_id=%u\n",
> > +rx_queue_id, rx_port_id);  return 0;  } #endif
> > +
> > + if (p->recycle_rx_descriptors_refill == NULL) return 0;
> > +
> > + /* Replenish the Rx descriptors with the recycling
> > + * into Rx mbuf ring.
> > + */
> > + p->recycle_rx_descriptors_refill(qd, nb_mbufs);
> > +
> > + return nb_mbufs;
> > +}
> > +
> >  /**
> >   * @warning
> >   * @b EXPERIMENTAL: this API may change without prior notice diff
> > --git a/lib/ethdev/rte_ethdev_core.h b/lib/ethdev/rte_ethdev_core.h
> > index dcf8adab92..a2e6ea6b6c 100644
> > --- a/lib/ethdev/rte_ethdev_core.h
> > +++ b/lib/ethdev/rte_ethdev_core.h
> > @@ -56,6 +56,13 @@ typedef int (*eth_rx_descriptor_status_t)(void
> > *rxq, uint16_t offset);
> >  /** @internal Check the status of a Tx descriptor */  typedef int
> > (*eth_tx_descriptor_status_t)(void *txq, uint16_t offset);
> >
> > +/** @internal Copy used mbufs from Tx mbuf ring into Rx mbuf ring */
> > +typedef uint16_t (*eth_recycle_tx_mbufs_reuse_t)(void *txq,  struct
> > +rte_eth_recycle_rxq_info *recycle_rxq_info);
> > +
> > +/** @internal Refill Rx descriptors with the recycling mbufs */
> > +typedef void (*eth_recycle_rx_descriptors_refill_t)(void *rxq,
> > +uint16_t nb);
> > +
> >  /**
> >   * @internal
> >   * Structure used to hold opaque pointers to internal ethdev Rx/Tx @@
> > -90,9 +97,11 @@ struct rte_eth_fp_ops {
> >          eth_rx_queue_count_t rx_queue_count;
> >          /** Check the status of a Rx descriptor. */
> >          eth_rx_descriptor_status_t rx_descriptor_status;
> > + /** Refill Rx descriptors with the recycling mbufs. */
> > + eth_recycle_rx_descriptors_refill_t recycle_rx_descriptors_refill;
> > I am afraid we can't put new fields here without ABI breakage.
> >
> > Agree
> >
> > It has to be below rxq.
> > Now thinking about current layout probably not the best one, and when
> > introducing this struct, I should probably put rxq either on the top
> > of the struct, or on the next cache line.
> > But such change is not possible right now anyway.
> > Same story for txq.
> >
> > Thus we should rearrange the structure like below：
> > struct rte_eth_fp_ops {
> >     struct rte_ethdev_qdata rxq;
> >          eth_rx_burst_t rx_pkt_burst;
> >          eth_rx_queue_count_t rx_queue_count;
> >          eth_rx_descriptor_status_t rx_descriptor_status;
> >        eth_recycle_rx_descriptors_refill_t recycle_rx_descriptors_refill;
> >               uintptr_t reserved1[2];
> > }
> 
> Yes, I think such layout will be better.
> The only problem here - we have to wait for 23.11 for that.
> 
Ok, if not this change, maybe we still need to wait. Because mbufs_recycle have other
ABI breakage. Such as the change for 'struct rte_eth_dev'.
> >
> >
> >          /** Rx queues data. */
> >          struct rte_ethdev_qdata rxq;
> > - uintptr_t reserved1[3];
> > + uintptr_t reserved1[2];
> >          /**@}*/
> >
> >          /**@{*/
> > @@ -106,9 +115,11 @@ struct rte_eth_fp_ops {
> >          eth_tx_prep_t tx_pkt_prepare;
> >          /** Check the status of a Tx descriptor. */
> >          eth_tx_descriptor_status_t tx_descriptor_status;
> > + /** Copy used mbufs from Tx mbuf ring into Rx. */
> > + eth_recycle_tx_mbufs_reuse_t recycle_tx_mbufs_reuse;
> >          /** Tx queues data. */
> >          struct rte_ethdev_qdata txq;
> > - uintptr_t reserved2[3];
> > + uintptr_t reserved2[2];
> >          /**@}*/
> >
> >  } __rte_cache_aligned;
> > diff --git a/lib/ethdev/version.map b/lib/ethdev/version.map index
> > 357d1a88c0..45c417f6bd 100644
> > --- a/lib/ethdev/version.map
> > +++ b/lib/ethdev/version.map
> > @@ -299,6 +299,10 @@ EXPERIMENTAL {
> >          rte_flow_action_handle_query_update;
> >          rte_flow_async_action_handle_query_update;
> >          rte_flow_async_create_by_index;
> > +
> > + # added in 23.07
> > + rte_eth_recycle_mbufs;
> > + rte_eth_recycle_rx_queue_info_get;
> >  };
> >
> >  INTERNAL {
> > --
> > 2.25.1
> >