On Thu, Dec 5, 2024, 07:40 David Marchand <david.marchand@redhat.com> wrote:

On Tue, Dec 3, 2024 at 10:13 PM Stephen Hemminger
<stephen@networkplumber.org> wrote:
>
> On Mon, 21 Oct 2024 01:52:46 +0000
> Wathsala Vithanage <wathsala.vithanage@arm.com> wrote:
>
> > Extend the ethdev library to enable the stashing of different data
> > objects, such as the ones listed below, into CPU caches directly
> > from the NIC.
> >
> > - Rx/Tx queue descriptors
> > - Rx packets
> > - Packet headers
> > - packet payloads
> > - Data of a packet at an offset from the start of the packet
> >
> > The APIs are designed in a hardware/vendor agnostic manner such that
> > supporting PMDs could use any capabilities available in the underlying
> > hardware for fine-grained stashing of data objects into a CPU cache
> > (e.g., Steering Tags int PCIe TLP Processing Hints).
> >
> > The API provides an interface to query the availability of stashing
> > capabilities, i.e., platform/NIC support, stashable object types, etc,
> > via the rte_eth_dev_stashing_capabilities_get interface.
> >
> > The function pair rte_eth_dev_stashing_rx_config_set and
> > rte_eth_dev_stashing_tx_config_set sets the stashing hint (the CPU,
> > cache level, and data object types) on the Rx and Tx queues.
> >
> > PMDs that support stashing must register their implementations with the
> > following eth_dev_ops callbacks, which are invoked by the ethdev
> > functions listed above.
> >
> > - stashing_capabilities_get
> > - stashing_rx_hints_set
> > - stashing_tx_hints_set
> >
> > Signed-off-by: Wathsala Vithanage <wathsala.vithanage@arm.com>
> > Reviewed-by: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>
> > Reviewed-by: Dhruv Tripathi <dhruv.tripathi@arm.com>
> >
> > ---
> > lib/ethdev/ethdev_driver.h | 66 +++++++++++++++
> > lib/ethdev/rte_ethdev.c | 120 +++++++++++++++++++++++++++
> > lib/ethdev/rte_ethdev.h | 161 +++++++++++++++++++++++++++++++++++++
> > lib/ethdev/version.map | 4 +
> > 4 files changed, 351 insertions(+)
> >
> > diff --git a/lib/ethdev/ethdev_driver.h b/lib/ethdev/ethdev_driver.h
> > index 1fd4562b40..7caaea54a8 100644
> > --- a/lib/ethdev/ethdev_driver.h
> > +++ b/lib/ethdev/ethdev_driver.h
> > @@ -1367,6 +1367,68 @@ enum rte_eth_dev_operation {
> > typedef uint64_t (*eth_get_restore_flags_t)(struct rte_eth_dev *dev,
> > enum rte_eth_dev_operation op);
> >
> > +/**
> > + * @internal
> > + * Set cache stashing hints in Rx queue.
> > + *
> > + * @param dev
> > + * Port (ethdev) handle.
> > + * @param queue_id
> > + * Rx queue.
> > + * @param config
> > + * Stashing hints configuration for the queue.
> > + *
> > + * @return
> > + * -ENOTSUP if the device or the platform does not support cache stashing.
> > + * -ENOSYS if the underlying PMD hasn't implemented cache stashing feature.
> > + * -EINVAL on invalid arguments.
> > + * 0 on success.
> > + */
> > +typedef int (*eth_stashing_rx_hints_set_t)(struct rte_eth_dev *dev, uint16_t queue_id,
> > + struct rte_eth_stashing_config *config);
> > +
> > +/**
> > + * @internal
> > + * Set cache stashing hints in Tx queue.
> > + *
> > + * @param dev
> > + * Port (ethdev) handle.
> > + * @param queue_id
> > + * Tx queue.
> > + * @param config
> > + * Stashing hints configuration for the queue.
> > + *
> > + * @return
> > + * -ENOTSUP if the device or the platform does not support cache stashing.
> > + * -ENOSYS if the underlying PMD hasn't implemented cache stashing feature.
> > + * -EINVAL on invalid arguments.
> > + * 0 on success.
> > + */
> > +typedef int (*eth_stashing_tx_hints_set_t)(struct rte_eth_dev *dev, uint16_t queue_id,
> > + struct rte_eth_stashing_config *config);
> > +
> > +/**
> > + * @internal
> > + * Get cache stashing object types supported in the ethernet device.
> > + * The return value indicates availability of stashing hints support
> > + * in the hardware and the PMD.
> > + *
> > + * @param dev
> > + * Port (ethdev) handle.
> > + * @param objects
> > + * PMD sets supported bits on return.
> > + *
> > + * @return
> > + * -ENOTSUP if the device or the platform does not support cache stashing.
> > + * -ENOSYS if the underlying PMD hasn't implemented cache stashing feature.
> > + * -EINVAL on NULL values for types or hints parameters.
> > + * On return, types and hints parameters will have bits set for supported
> > + * object types and hints.
> > + * 0 on success.
> > + */
> > +typedef int (*eth_stashing_capabilities_get_t)(struct rte_eth_dev *dev,
> > + uint16_t *objects);
> > +
> > /**
> > * @internal A structure containing the functions exported by an Ethernet driver.
> > */
> > @@ -1393,6 +1455,10 @@ struct eth_dev_ops {
> > eth_mac_addr_remove_t mac_addr_remove; /**< Remove MAC address */
> > eth_mac_addr_add_t mac_addr_add; /**< Add a MAC address */
> > eth_mac_addr_set_t mac_addr_set; /**< Set a MAC address */
> > + eth_stashing_rx_hints_set_t stashing_rx_hints_set; /**< Set Rx cache stashing*/
> > + eth_stashing_tx_hints_set_t stashing_tx_hints_set; /**< Set Tx cache stashing*/
> > + /** Get supported stashing hints*/
> > + eth_stashing_capabilities_get_t stashing_capabilities_get;
> > /** Set list of multicast addresses */
> > eth_set_mc_addr_list_t set_mc_addr_list;
> > mtu_set_t mtu_set; /**< Set MTU */
>
> Since eth_dev_ops is visible in application binary, it is part of the ABI.
> Therefore it can not be changed until 25.11 release.

The layout of eth_dev_ops is not exposed to applications as it is in a
private header.
Could you clarify where you see a breakage for an application?

I see an ABI breakage for out of tree drivers though.
This could be avoided by moving those added ops at the end of the struct?

--
David Marchand