> From: Ferruh Yigit [mailto:ferruh.yi...@amd.com]
> Sent: Friday, 12 January 2024 12.34
>
> On 1/11/2024 3:17 PM, jer...@marvell.com wrote:
> > From: Jerin Jacob <jer...@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.
[...]
> > +/**
> > + * @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).
> >
>
> Above is good, but do you think does it help to mention that intended
> usacase is QoS, to address the risk Bruce mentioned?
A better way to address the risk is to mention that:
1. there is no need to call this function before rte_eth_tx_burst(), and
2. tx_descriptor_status() has better performance for checking a threshold than
this function.
> > /**
> > * @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 used Tx descriptors. */
> > + eth_tx_queue_count_t tx_queue_count;
> >
>
> Similarly, can you please move it above 'tx_descriptor_status'?
No. I think struct rte_eth_fp_ops is part of the public API, so moving down
tx_descriptor_status and recycle_tx_mbufs_reuse would break the API.
>
>
> > + uintptr_t reserved2[1];
> > /**@}*/
> >
> > } __rte_cache_aligned;
