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

[Ferruh Yigit <ferruh.yigit@amd.com>]

On 6/6/2023 9:34 AM, Konstantin Ananyev wrote:
> 
> 
>>
>> [...]
>>>> 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.
> 
> Yes, that was my thought, that's why I was surprise that in the comments we have:
> " Currently, the rte_eth_recycle_mbufs() function can only support one-time pairing
> * between the receive queue and transmit queue. Do not pair one receive queue with
>  * multiple transmit queues or pair one transmit queue with multiple receive queues,
>  * in order to avoid memory error rewriting."
> 

I guess that is from previous versions of the set, it can be good to
address limitations/restrictions again with latest version.


>>
>>>
>>>> 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'.
> 
> Ok by me.
> 
>>>>
>>>>
>>>>          /** 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
>>>>