[dpdk-dev] [v2] ethdev: support Tx queue used count

[Konstantin Ananyev]

> From: Jerin Jacob <jerinj at marvell.com>
> 
> Introduce a new API to retrieve the number of used 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 <jerinj at marvell.com>
> Reviewed-by: Andrew Rybchenko <andrew.rybchenko at oktetlabs.ru>
> Acked-by: Morten Brørup <mb at smartsharesystems.com>
> ---
>  devtools/libabigail.abignore           |  3 +
>  doc/guides/nics/features.rst           | 10 ++++
>  doc/guides/nics/features/default.ini   |  1 +
>  doc/guides/rel_notes/release_24_03.rst |  5 ++
>  lib/ethdev/ethdev_driver.h             |  2 +
>  lib/ethdev/ethdev_private.c            |  1 +
>  lib/ethdev/ethdev_trace_points.c       |  3 +
>  lib/ethdev/rte_ethdev.h                | 80 ++++++++++++++++++++++++++
>  lib/ethdev/rte_ethdev_core.h           |  7 ++-
>  lib/ethdev/rte_ethdev_trace_fp.h       |  8 +++
>  lib/ethdev/version.map                 |  1 +
>  11 files changed, 120 insertions(+), 1 deletion(-)
> 
> v2:
> - Rename _nic_features_tx_queue_used_count to _nic_features_tx_queue_count
> - Fix trace emission of case fops->tx_queue_count == NULL
> - Rename tx_queue_id to queue_id in implementation symbols and prints
> - Added "goto out" for better error handling
> - Add release note
> - Added libabigail suppression rule for the reserved2 field update
> - Fix all ordering and grouping, empty line comment from Ferruh
> - Added following notes in doxygen documentation for better clarity on API usage
>  * @note There is no requirement to call this function before rte_eth_tx_burst() invocation.
>  * @note Utilize this function exclusively when the caller needs to determine the used queue count
>  * across all descriptors of a Tx queue. If the use case only involves checking the status of a
>  * specific descriptor slot, opt for rte_eth_tx_descriptor_status() instead.
> 
> rfc..v1:
> - Updated API similar to rte_eth_rx_queue_count() where it returns
> "used" count instead of "free" count
> 
> diff --git a/devtools/libabigail.abignore b/devtools/libabigail.abignore
> index 21b8cd6113..d6e98c6f52 100644
> --- a/devtools/libabigail.abignore
> +++ b/devtools/libabigail.abignore
> @@ -33,3 +33,6 @@
>  ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
>  ; Temporary exceptions till next major ABI version ;
>  ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
> +[suppress_type]
> +	name = rte_eth_fp_ops
> +	has_data_member_inserted_between = {offset_of(reserved2), end}
> diff --git a/doc/guides/nics/features.rst b/doc/guides/nics/features.rst
> index f7d9980849..f38941c719 100644
> --- a/doc/guides/nics/features.rst
> +++ b/doc/guides/nics/features.rst
> @@ -697,6 +697,16 @@ or "Unavailable."
>  * **[related]    API**: ``rte_eth_tx_descriptor_status()``.
> 
> 
> +.. _nic_features_tx_queue_count:
> +
> +Tx queue count
> +--------------
> +
> +Supports to get the number of used descriptors of a Tx queue.
> +
> +* **[implements] eth_dev_ops**: ``tx_queue_count``.
> +* **[related] API**: ``rte_eth_tx_queue_count()``.
> +
>  .. _nic_features_basic_stats:
> 
>  Basic stats
> diff --git a/doc/guides/nics/features/default.ini b/doc/guides/nics/features/default.ini
> index 6d50236292..5115963136 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 queue count       =
>  Basic stats          =
>  Extended stats       =
>  Stats per queue      =
> diff --git a/doc/guides/rel_notes/release_24_03.rst b/doc/guides/rel_notes/release_24_03.rst
> index c4fc8ad583..16dd367178 100644
> --- a/doc/guides/rel_notes/release_24_03.rst
> +++ b/doc/guides/rel_notes/release_24_03.rst
> @@ -65,6 +65,11 @@ New Features
>    * Added ``RTE_FLOW_ITEM_TYPE_RANDOM`` to match random value.
>    * Added ``RTE_FLOW_FIELD_RANDOM`` to represent it in field ID struct.
> 
> +* ** Support for getting the number of used descriptors of a Tx queue. **
> +
> +  * Added a fath path function ``rte_eth_tx_queue_count`` to get the number of used
> +    descriptors of a Tx queue.
> +
> 
>  Removed Items
>  -------------
> diff --git a/lib/ethdev/ethdev_driver.h b/lib/ethdev/ethdev_driver.h
> index b482cd12bb..f05f68a67c 100644
> --- a/lib/ethdev/ethdev_driver.h
> +++ b/lib/ethdev/ethdev_driver.h
> @@ -58,6 +58,8 @@ struct rte_eth_dev {
>  	eth_rx_queue_count_t rx_queue_count;
>  	/** Check the status of a Rx descriptor */
>  	eth_rx_descriptor_status_t rx_descriptor_status;
> +	/** Get the number of used Tx descriptors */
> +	eth_tx_queue_count_t tx_queue_count;
>  	/** Check the status of a Tx descriptor */
>  	eth_tx_descriptor_status_t tx_descriptor_status;
>  	/** Pointer to PMD transmit mbufs reuse function */
> diff --git a/lib/ethdev/ethdev_private.c b/lib/ethdev/ethdev_private.c
> index a656df293c..626524558a 100644
> --- a/lib/ethdev/ethdev_private.c
> +++ b/lib/ethdev/ethdev_private.c
> @@ -273,6 +273,7 @@ eth_dev_fp_ops_setup(struct rte_eth_fp_ops *fpo,
>  	fpo->tx_pkt_prepare = dev->tx_pkt_prepare;
>  	fpo->rx_queue_count = dev->rx_queue_count;
>  	fpo->rx_descriptor_status = dev->rx_descriptor_status;
> +	fpo->tx_queue_count = dev->tx_queue_count;
>  	fpo->tx_descriptor_status = dev->tx_descriptor_status;
>  	fpo->recycle_tx_mbufs_reuse = dev->recycle_tx_mbufs_reuse;
>  	fpo->recycle_rx_descriptors_refill = dev->recycle_rx_descriptors_refill;
> diff --git a/lib/ethdev/ethdev_trace_points.c b/lib/ethdev/ethdev_trace_points.c
> index 91f71d868b..bd6dd4e78a 100644
> --- a/lib/ethdev/ethdev_trace_points.c
> +++ b/lib/ethdev/ethdev_trace_points.c
> @@ -37,6 +37,9 @@ RTE_TRACE_POINT_REGISTER(rte_eth_trace_call_rx_callbacks,
>  RTE_TRACE_POINT_REGISTER(rte_eth_trace_call_tx_callbacks,
>  	lib.ethdev.call_tx_callbacks)
> 
> +RTE_TRACE_POINT_REGISTER(rte_eth_trace_tx_queue_count,
> +	lib.ethdev.tx_queue_count)
> +
>  RTE_TRACE_POINT_REGISTER(rte_eth_trace_iterator_init,
>  	lib.ethdev.iterator_init)
> 
> diff --git a/lib/ethdev/rte_ethdev.h b/lib/ethdev/rte_ethdev.h
> index b7f52e03a5..2687c23fa6 100644
> --- a/lib/ethdev/rte_ethdev.h
> +++ b/lib/ethdev/rte_ethdev.h
> @@ -6823,6 +6823,86 @@ 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 used descriptors of a Tx queue
> + *
> + * This function retrieves the number of used descriptors of 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).
> + *
> + * Since it's a fast-path function, no check is performed on port_id and
> + * queue_id. The caller must therefore ensure that the port is enabled
> + * and the queue is configured and running.
> + *
> + * @param port_id
> + *   The port identifier of the device.
> + * @param 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
> + *  The number of used descriptors in the specific queue, or:
> + *   - (-ENODEV) if *port_id* is invalid. Enabled only when RTE_ETHDEV_DEBUG_TX is enabled
> + *   - (-EINVAL) if *queue_id* is invalid. Enabled only when RTE_ETHDEV_DEBUG_TX is enabled
> + *   - (-ENOTSUP) if the device does not support this function.
> + *
> + * @note This function is designed for fast-path use.
> + * @note There is no requirement to call this function before rte_eth_tx_burst() invocation.
> + * @note Utilize this function exclusively when the caller needs to determine the used queue count
> + * across all descriptors of a Tx queue. If the use case only involves checking the status of a
> + * specific descriptor slot, opt for rte_eth_tx_descriptor_status() instead.
> + */
> +
> +__rte_experimental
> +static inline int
> +rte_eth_tx_queue_count(uint16_t port_id, uint16_t queue_id)
> +{
> +	struct rte_eth_fp_ops *fops;
> +	void *qd;
> +	int rc;
> +
> +#ifdef RTE_ETHDEV_DEBUG_TX
> +	if (port_id >= RTE_MAX_ETHPORTS || !rte_eth_dev_is_valid_port(port_id)) {
> +		RTE_ETHDEV_LOG_LINE(ERR, "Invalid port_id=%u", port_id);
> +		rc = -ENODEV;
> +		goto out;
> +	}
> +
> +	if (queue_id >= RTE_MAX_QUEUES_PER_PORT) {
> +		RTE_ETHDEV_LOG_LINE(ERR, "Invalid queue_id=%u for port_id=%u",
> +				    queue_id, port_id);
> +		rc = -EINVAL;
> +		goto out;
> +	}
> +#endif
> +
> +	/* Fetch pointer to Tx queue data */
> +	fops = &rte_eth_fp_ops[port_id];
> +	qd = fops->txq.data[queue_id];
> +
> +#ifdef RTE_ETHDEV_DEBUG_TX
> +	if (qd == NULL) {
> +		RTE_ETHDEV_LOG_LINE(ERR, "Invalid queue_id=%u for port_id=%u",
> +				    queue_id, port_id);
> +		rc = -EINVAL;
> +		goto out;
> +	}
> +#endif
> +	if (fops->tx_queue_count == NULL) {
> +		rc = -ENOTSUP;
> +		goto out;
> +	}
> +
> +	rc = fops->tx_queue_count(qd);
> +
> +out:
> +	rte_eth_trace_tx_queue_count(port_id, 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..a18f242ca4 100644
> --- a/lib/ethdev/rte_ethdev_core.h
> +++ b/lib/ethdev/rte_ethdev_core.h
> @@ -50,6 +50,9 @@ typedef uint32_t (*eth_rx_queue_count_t)(void *rxq);
>  /** @internal Check the status of a Rx descriptor */
>  typedef int (*eth_rx_descriptor_status_t)(void *rxq, uint16_t offset);
> 
> +/** @internal Get number of used descriptors on a transmit queue. */
> +typedef int (*eth_tx_queue_count_t)(void *txq);
> +
>  /** @internal Check the status of a Tx descriptor */
>  typedef int (*eth_tx_descriptor_status_t)(void *txq, uint16_t offset);
> 
> @@ -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 used Tx descriptors. */
> +	eth_tx_queue_count_t tx_queue_count;
> +	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..40b6e4756b 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_count,
> +	RTE_TRACE_POINT_ARGS(uint16_t port_id, uint16_t queue_id, int rc),
> +	rte_trace_point_emit_u16(port_id);
> +	rte_trace_point_emit_u16(queue_id);
> +	rte_trace_point_emit_int(rc);
> +)
> +
>  #ifdef __cplusplus
>  }
>  #endif
> diff --git a/lib/ethdev/version.map b/lib/ethdev/version.map
> index a050baab0f..73a788d91a 100644
> --- a/lib/ethdev/version.map
> +++ b/lib/ethdev/version.map
> @@ -319,6 +319,7 @@ EXPERIMENTAL {
> 
>  	# added in 24.03
>  	rte_eth_find_rss_algo;
> +	rte_eth_tx_queue_count;
>  };
> 
>  INTERNAL {
> --

Acked-by: Konstantin Ananyev <konstantin.ananyev at huawei.com>

> 2.43.0