RE: [PATCH] doc: announce ethdev operation struct changes

["Morten Brørup" <mb@smartsharesystems.com>]

> From: Thomas Monjalon [mailto:thomas@monjalon.net]
> Sent: Friday, 28 July 2023 17.38
> 
> 28/07/2023 17:33, Morten Brørup:
> > > From: Thomas Monjalon [mailto:thomas@monjalon.net]
> > > Sent: Friday, 28 July 2023 17.20
> > >
> > > 28/07/2023 17:08, Morten Brørup:
> > > > > From: Thomas Monjalon [mailto:thomas@monjalon.net]
> > > > > Sent: Friday, 28 July 2023 16.57
> > > > >
> > > > > 04/07/2023 10:10, Feifei Wang:
> > > > > > To support mbufs recycle mode, announce the coming ABI changes
> > > > > > from DPDK 23.11.
> > > > > >
> > > > > > Signed-off-by: Feifei Wang <feifei.wang2@arm.com>
> > > > > > Reviewed-by: Ruifeng Wang <ruifeng.wang@arm.com>
> > > > > > ---
> > > > > >  doc/guides/rel_notes/deprecation.rst | 4 ++++
> > > > > >  1 file changed, 4 insertions(+)
> > > > > >
> > > > > > diff --git a/doc/guides/rel_notes/deprecation.rst
> > > > > b/doc/guides/rel_notes/deprecation.rst
> > > > > > index 66431789b0..c7e1ffafb2 100644
> > > > > > --- a/doc/guides/rel_notes/deprecation.rst
> > > > > > +++ b/doc/guides/rel_notes/deprecation.rst
> > > > > > @@ -118,6 +118,10 @@ Deprecation Notices
> > > > > >    The legacy actions should be removed
> > > > > >    once ``MODIFY_FIELD`` alternative is implemented in drivers.
> > > > > >
> > > > > > +* ethdev: The Ethernet device data structure ``struct rte_eth_dev``
> and
> > > > > > +  the fast-path ethdev flat array ``struct rte_eth_fp_ops`` will be
> > > updated
> > > > > > +  with new fields to support mbufs recycle mode from DPDK 23.11.
> > > >
> > > > Existing fields will also be moved around [1]:
> > > >
> > > > @@ -83,15 +90,17 @@  struct rte_eth_fp_ops {
> > > >  	 * Rx fast-path functions and related data.
> > > >  	 * 64-bit systems: occupies first 64B line
> > > >  	 */
> > > > +	/** Rx queues data. */
> > > > +	struct rte_ethdev_qdata rxq;
> > > >  	/** PMD receive function. */
> > > >  	eth_rx_burst_t rx_pkt_burst;
> > > >  	/** Get the number of used Rx descriptors. */
> > > >  	eth_rx_queue_count_t rx_queue_count;
> > > >  	/** Check the status of a Rx descriptor. */
> > > >  	eth_rx_descriptor_status_t rx_descriptor_status;
> > > > -	/** Rx queues data. */
> > > > -	struct rte_ethdev_qdata rxq;
> > > > -	uintptr_t reserved1[3];
> > > > +	/** Refill Rx descriptors with the recycling mbufs. */
> > > > +	eth_recycle_rx_descriptors_refill_t
> recycle_rx_descriptors_refill;
> > > > +	uintptr_t reserved1[2];
> > > >  	/**@}*/
> > > >
> > > >  	/**@{*/
> > > > @@ -99,15 +108,17 @@  struct rte_eth_fp_ops {
> > > >  	 * Tx fast-path functions and related data.
> > > >  	 * 64-bit systems: occupies second 64B line
> > > >  	 */
> > > > +	/** Tx queues data. */
> > > > +	struct rte_ethdev_qdata txq;
> > > >  	/** PMD transmit function. */
> > > >  	eth_tx_burst_t tx_pkt_burst;
> > > >  	/** PMD transmit prepare function. */
> > > >  	eth_tx_prep_t tx_pkt_prepare;
> > > >  	/** Check the status of a Tx descriptor. */
> > > >  	eth_tx_descriptor_status_t tx_descriptor_status;
> > > > -	/** Tx queues data. */
> > > > -	struct rte_ethdev_qdata txq;
> > > > -	uintptr_t reserved2[3];
> > > > +	/** Copy used mbufs from Tx mbuf ring into Rx. */
> > > > +	eth_recycle_tx_mbufs_reuse_t recycle_tx_mbufs_reuse;
> > > > +	uintptr_t reserved2[2];
> > > >  	/**@}*/
> > >
> > > Removing existing fields should be announced explicitly.
> >
> > Agreed. And the patch misses this. The "rxq" and "txq" fields are not being
> removed, they are being moved up in the structures. Your comment about
> explicit mentioning still applies!
> >
> > If there's no time to wait for a new patch version from Feifei, perhaps you
> improve the description while merging.
> 
> If it's only moving fields, we can skip.

OK. Thank you for elaborating.

> The real change is the size of the reserved fields,
> so it looks acceptable without notice.

Agree.

Thoughts for later: We should perhaps document that changing the size of reserved fields is acceptable. And with that, if completely removing a reserved field is also acceptable or not.