> -----Original Message-----
> From: jer...@marvell.com <jer...@marvell.com>
> Sent: Tuesday, December 19, 2023 5:30 PM
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> <cristian.dumitre...@intel.com>; Jerin Jacob <jer...@marvell.com>
> Subject: [dpdk-dev] [RFC] ethdev: support Tx queue free descriptor query
>
> From: Jerin Jacob <jer...@marvell.com>
>
> Introduce a new API to retrieve the number of available free descriptors
> in a Tx queue. Applications can leverage this API in the fast path to
> inspect the Tx queue occupancy and take appropriate actions based on the
> available free descriptors.
>
> A notable use case could be implementing Random Early Discard (RED)
> in software based on Tx queue occupancy.
>
> Signed-off-by: Jerin Jacob <jer...@marvell.com>
> ---
> doc/guides/nics/features.rst | 10 ++++
> doc/guides/nics/features/default.ini | 1 +
> lib/ethdev/ethdev_trace_points.c | 3 ++
> lib/ethdev/rte_ethdev.h | 78 ++++++++++++++++++++++++++++
> lib/ethdev/rte_ethdev_core.h | 7 ++-
> lib/ethdev/rte_ethdev_trace_fp.h | 8 +++
> 6 files changed, 106 insertions(+), 1 deletion(-)
>
> diff --git a/doc/guides/nics/features.rst b/doc/guides/nics/features.rst
> index f7d9980849..9d6655473a 100644
> --- a/doc/guides/nics/features.rst
> +++ b/doc/guides/nics/features.rst
> @@ -962,6 +962,16 @@ management (see :doc:`../prog_guide/power_man` for
> more details).
>
> * **[implements] eth_dev_ops**: ``get_monitor_addr``
>
> +.. _nic_features_tx_queue_free_desc_query:
> +
> +Tx queue free descriptor query
> +------------------------------
> +
> +Supports to get the number of free descriptors in a Tx queue.
> +
> +* **[implements] eth_dev_ops**: ``tx_queue_free_desc_get``.
> +* **[related] API**: ``rte_eth_tx_queue_free_desc_get()``.
> +
> .. _nic_features_other:
>
> Other dev ops not represented by a Feature
> diff --git a/doc/guides/nics/features/default.ini
> b/doc/guides/nics/features/default.ini
> index 806cb033ff..b30002b1c1 100644
> --- a/doc/guides/nics/features/default.ini
> +++ b/doc/guides/nics/features/default.ini
> @@ -59,6 +59,7 @@ Packet type parsing =
> Timesync =
> Rx descriptor status =
> Tx descriptor status =
> +Tx free descriptor query =
> Basic stats =
> Extended stats =
> Stats per queue =
> diff --git a/lib/ethdev/ethdev_trace_points.c
> b/lib/ethdev/ethdev_trace_points.c
> index 91f71d868b..346f37f2e4 100644
> --- a/lib/ethdev/ethdev_trace_points.c
> +++ b/lib/ethdev/ethdev_trace_points.c
> @@ -481,6 +481,9 @@
> RTE_TRACE_POINT_REGISTER(rte_eth_trace_count_aggr_ports,
> RTE_TRACE_POINT_REGISTER(rte_eth_trace_map_aggr_tx_affinity,
> lib.ethdev.map_aggr_tx_affinity)
>
> +RTE_TRACE_POINT_REGISTER(rte_eth_trace_tx_queue_free_desc_get,
> + lib.ethdev.tx_queue_free_desc_get)
> +
> RTE_TRACE_POINT_REGISTER(rte_flow_trace_copy,
> lib.ethdev.flow.copy)
>
> diff --git a/lib/ethdev/rte_ethdev.h b/lib/ethdev/rte_ethdev.h
> index 77331ce652..033fcb8c9b 100644
> --- a/lib/ethdev/rte_ethdev.h
> +++ b/lib/ethdev/rte_ethdev.h
> @@ -6802,6 +6802,84 @@ rte_eth_recycle_mbufs(uint16_t rx_port_id, uint16_t
> rx_queue_id,
> __rte_experimental
> int rte_eth_buffer_split_get_supported_hdr_ptypes(uint16_t port_id, uint32_t
> *ptypes, int num);
>
> +/**
> + * @warning
> + * @b EXPERIMENTAL: this API may change, or be removed, without prior notice
> + *
> + * Get the number of free descriptors in a Tx queue.
> + *
> + * This function retrieves the number of available free descriptors in a
> + * transmit queue. Applications can use this API in the fast path to inspect
> + * Tx queue occupancy and take appropriate actions based on the available
> + * free descriptors. An example action could be implementing the
> + * Random Early Discard (RED).
> + *
> + * If there are no packets in the Tx queue, the function returns the value
> + * of `nb_tx_desc` provided during the initialization of the Tx queue using
> + * rte_eth_tx_queue_setup(), signifying that all descriptors are free.
> + *
> + * @param port_id
> + * The port identifier of the device.
> + * @param tx_queue_id
> + * The index of the transmit queue.
> + * The value must be in the range [0, nb_tx_queue - 1] previously supplied
> + * to rte_eth_dev_configure().
> + * @return
> + * - (<= UINT16_MAX) Number of free descriptors in a Tx queue
> + * - (> UINT16_MAX) if error. Enabled only when RTE_ETHDEV_DEBUG_TX is
> enabled
> + *
> + * @note This function is designed for fast-path use.
> + *
> + */
> +__rte_experimental
> +static inline uint32_t
> +rte_eth_tx_queue_free_desc_get(uint16_t port_id, uint16_t tx_queue_id)
> +{
> + struct rte_eth_fp_ops *fops;
> + uint32_t rc;
> + void *qd;
> +
> +#ifdef RTE_ETHDEV_DEBUG_TX
> + rc = UINT32_MAX;
> + if (port_id >= RTE_MAX_ETHPORTS || tx_queue_id >=
> RTE_MAX_QUEUES_PER_PORT) {
> + RTE_ETHDEV_LOG(ERR, "Invalid port_id=%u or
> tx_queue_id=%u\n",
> + port_id, tx_queue_id);
> +
> + rte_eth_trace_tx_queue_free_desc_get(port_id, tx_queue_id,
> rc);
> + return rc;
> + }
> +#endif
> +
> + /* Fetch pointer to Tx queue data */
> + fops = &rte_eth_fp_ops[port_id];
> + qd = fops->txq.data[tx_queue_id];
> +
> +#ifdef RTE_ETHDEV_DEBUG_TX
> + RTE_ETH_VALID_PORTID_OR_ERR_RET(port_id, 0);
> +
> + if (qd == NULL) {
> + RTE_ETHDEV_LOG(ERR, "Invalid Tx queue_id=%u for
> port_id=%u\n",
> + tx_queue_id, port_id);
> +
> + rte_eth_trace_tx_queue_free_desc_get(port_id, tx_queue_id,
> rc);
> + return rc;
> + }
> +
> + if (fops->tx_queue_free_desc_get == NULL) {
> + RTE_ETHDEV_LOG(ERR, "tx_queue_free_desc_get callback not
> implementedd Tx queue_id=%u for port_id=%u\n",
> + tx_queue_id, port_id);
> +
> + rte_eth_trace_tx_queue_free_desc_get(port_id, tx_queue_id,
> rc);
> + return rc;
> + }
> +#endif
> + rc = fops->tx_queue_free_desc_get(qd);
> +
> + rte_eth_trace_tx_queue_free_desc_get(port_id, tx_queue_id, rc);
> +
> + return rc;
> +}
> +
> #ifdef __cplusplus
> }
> #endif
> diff --git a/lib/ethdev/rte_ethdev_core.h b/lib/ethdev/rte_ethdev_core.h
> index 4bfaf79c6c..5b7ee66ee7 100644
> --- a/lib/ethdev/rte_ethdev_core.h
> +++ b/lib/ethdev/rte_ethdev_core.h
> @@ -60,6 +60,9 @@ typedef uint16_t (*eth_recycle_tx_mbufs_reuse_t)(void
> *txq,
> /** @internal Refill Rx descriptors with the recycling mbufs */
> typedef void (*eth_recycle_rx_descriptors_refill_t)(void *rxq, uint16_t nb);
>
> +/** @internal Get the number of free descriptors count of a Tx queue */
> +typedef uint16_t (*eth_tx_queue_free_desc_get_t)(void *txq);
> +
> /**
> * @internal
> * Structure used to hold opaque pointers to internal ethdev Rx/Tx
> @@ -116,7 +119,9 @@ struct rte_eth_fp_ops {
> 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;
> - uintptr_t reserved2[2];
> + /** Get the number of free descriptors count of a Tx queue. */
> + eth_tx_queue_free_desc_get_t tx_queue_free_desc_get;
> + uintptr_t reserved2[1];
> /**@}*/
>
> } __rte_cache_aligned;
> diff --git a/lib/ethdev/rte_ethdev_trace_fp.h
> b/lib/ethdev/rte_ethdev_trace_fp.h
> index 186271c9ff..2c57b39bd2 100644
> --- a/lib/ethdev/rte_ethdev_trace_fp.h
> +++ b/lib/ethdev/rte_ethdev_trace_fp.h
> @@ -73,6 +73,14 @@ RTE_TRACE_POINT_FP(
> rte_trace_point_emit_u64(count);
> )
>
> +RTE_TRACE_POINT_FP(
> + rte_eth_trace_tx_queue_free_desc_get,
> + RTE_TRACE_POINT_ARGS(uint16_t port_id, uint16_t tx_queue_id,
> uint32_t nb_free_desc),
> + rte_trace_point_emit_u16(port_id);
> + rte_trace_point_emit_u16(tx_queue_id);
> + rte_trace_point_emit_u32(nb_free_desc);
> +)
> +
> #ifdef __cplusplus
> }
> #endif
> --
> 2.43.0
Hi Jerin,
I think having an API to get the number of free descriptors per queue is a good
idea. Why have it only for TX queues and not for RX queues as well?
Regards,
Cristian
