Re: [dpdk-dev] [RFC] ethdev: support Tx queue free descriptor query

[Thomas Monjalon <thomas@monjalon.net>]

04/01/2024 15:21, Konstantin Ananyev:
> 
> > > > Introduce a new API to retrieve the number of available free 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>
> > >
> > > I think having an API to get the number of free descriptors per queue is a good idea. Why have it only for TX queues and not for RX
> > queues as well?
> > 
> > I see no harm in adding for Rx as well. I think, it is better to have
> > separate API for each instead of adding argument as it is fast path
> > API.
> > If so, we could add a new API when there is any PMD implementation or
> > need for this.
> 
> I think for RX we already have similar one:
> /** @internal Get number of used descriptors on a receive queue. */
> typedef uint32_t (*eth_rx_queue_count_t)(void *rxq);

rte_eth_rx_queue_count() gives the number of Rx used descriptors
rte_eth_rx_descriptor_status() gives the status of one Rx descriptor
rte_eth_tx_descriptor_status() gives the status of one Tx descriptor

This patch is adding a function to get Tx available descriptors,
rte_eth_tx_queue_free_desc_get().
I can see a symmetry with rte_eth_rx_queue_count().
For consistency I would rename it to rte_eth_tx_queue_free_count().

Should we add rte_eth_tx_queue_count() and rte_eth_rx_queue_free_count()?