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

[Thomas Monjalon <thomas@monjalon.net>]

05/01/2024 10:57, Jerin Jacob:
> On Thu, Jan 4, 2024 at 11:59 PM Thomas Monjalon <thomas@monjalon.net> wrote:
> >
> > 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()?
> 
> IMO, rte_eth_rx_queue_free_count() is enough as
> used count =  total desc number(configured via nb_tx_desc with
> rte_eth_tx_queue_setup())  - free count

I'm fine with that.