[dpdk-dev] [v1] ethdev: support Tx queue used count

[Morten Brørup]

> From: jerinj at marvell.com [mailto:jerinj at marvell.com]
> Sent: Thursday, 11 January 2024 16.18
> 
> 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>
> ---

Generally looks good.

Only some minor suggestions/comments regarding rte_eth_tx_queue_count():

uint16_t tx_queue_id -> uint16_t queue_id
Everywhere, also in rte_ethdev_trace_fp.h.

Similarly in the log messages:
"Invalid Tx queue_id" -> "Invalid queue_id"

I don't like that rc = -EINVAL is reused instead of set explicitly for each error case.

Also, the return value -ENOTSUP is not traced.

Consider using an "out" label for a common return path to include trace, e.g.:

/**
 * @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.
 */
__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;
}


With or without suggested changes:

Acked-by: Morten Brørup <mb at smartsharesystems.com>