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

[Jerin Jacob]

On Thu, Jan 11, 2024 at 9:47 PM Andrew Rybchenko
<andrew.rybchenko at oktetlabs.ru> wrote:
>
> On 1/11/24 18:17, jerinj at marvell.com wrote:
> > 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>
>
> with few nits below
> Reviewed-by: Andrew Rybchenko <andrew.rybchenko at oktetlabs.ru>
>
> [snip]
>
> > diff --git a/doc/guides/nics/features.rst b/doc/guides/nics/features.rst
> > index f7d9980849..0d5a8733fc 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_used_count:
>
> I'd stick to shorter version _nic_features_tx_queue_count to match API
> naming and feature title below.

Ack and change in v2.

> > +
> > +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_other:
> >
> >   Other dev ops not represented by a Feature
>
> [snip]
>
> > diff --git a/lib/ethdev/rte_ethdev.h b/lib/ethdev/rte_ethdev.h
> > index 21e3a21903..af59da9652 100644
> > --- a/lib/ethdev/rte_ethdev.h
> > +++ b/lib/ethdev/rte_ethdev.h
> > @@ -6803,6 +6803,80 @@ 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
> > + * tx_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 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
> > + *  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 tx_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;
> > +             rte_eth_trace_tx_queue_count(port_id, tx_queue_id, rc);
> > +             return rc;
> > +     }
> > +
> > +     rc = -EINVAL;
>
> Since it is a debug, IMHO it is better to keep the code simple and init
> rc in two below if bodies separately rather than relying on shared init
> here.

Ack and change in v2.


>
> > +     if (tx_queue_id >= RTE_MAX_QUEUES_PER_PORT) {
> > +             RTE_ETHDEV_LOG_LINE(ERR, "Invalid Tx queue_id=%u for port_id=%u",
> > +                                 tx_queue_id, port_id);
> > +             rte_eth_trace_tx_queue_count(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
> > +     if (qd == NULL) {
> > +             RTE_ETHDEV_LOG_LINE(ERR, "Invalid Tx queue_id=%u for port_id=%u",
> > +                                 tx_queue_id, port_id);
> > +             rte_eth_trace_tx_queue_count(port_id, tx_queue_id, rc);
> > +             return rc;
> > +     }
> > +#endif
> > +     if (fops->tx_queue_count == NULL)
>
> Don't we need trace here? (no strong opinion, just trying to understand
> why it is missing here)

It is missed by mistake. will fix in v2.

>
> > +             return -ENOTSUP;
> > +
> > +     rc = fops->tx_queue_count(qd);
> > +     rte_eth_trace_tx_queue_count(port_id, tx_queue_id, rc);
> > +
> > +     return rc;
> > +}
> >   #ifdef __cplusplus
> >   }
> >   #endif
>
> [snip]
>