ethdev: support Tx queue used count

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@marvell.com>
Reviewed-by: Andrew Rybchenko <andrew.rybchenko@oktetlabs.ru>
Acked-by: Morten Brørup <mb@smartsharesystems.com>
Acked-by: Konstantin Ananyev <konstantin.ananyev@huawei.com>
Reviewed-by: Ferruh Yigit <ferruh.yigit@amd.com>

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}

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

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      =

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
 -------------

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 */

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;

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)
 

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

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;

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

lib/ethdev/version.map

@@ -319,6 +319,7 @@ EXPERIMENTAL {
 
 	# added in 24.03
 	rte_eth_find_rss_algo;
+	rte_eth_tx_queue_count;
 };
 
 INTERNAL {