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

[Jerin Jacob]

On Fri, Jan 12, 2024 at 6:03 PM Konstantin Ananyev
<konstantin.ananyev at huawei.com> wrote:
>
> Hi Jerin,

Hi Konstantin,


>
> > 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>

> > @@ -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).
>
> Sorry, I probably misunderstood your previous mails, but wouldn't it be more convenient
> for user to have rte_eth_tx_queue_free_count(...) as fast-op, and
> have rte_eth_tx_queue_count(...) {  queue_txd_num - rte_eth_tx_queue_free_count(...);}
> as a slow-path function in rte_ethdev.c?

The general feedback is to align with the Rx queue API, specifically
rte_eth_rx_queue_count,
and it's noted that there is no equivalent rte_eth_rx_queue_free_count.

Given that the free count can be obtained by subtracting the used
count from queue_txd_num,
it is considered that either approach is acceptable.

The application configures queue_txd_num with tx_queue_setup(), and
the application can store that value in its structure.
This would enable fast-path usage for both base cases (whether the
application needs information about free or used descriptors)
with just one API(rte_eth_tx_queue_count())


> Konstantin