Re: [dpdk-dev] [RFC v2] doc: announce max Rx packet len field deprecation

[Matan Azrad <matan@nvidia.com>]

Hi

Looks very good direction - it will do some order here.

Will be also good to define what is MTU exactly:
Maximum Rx packet size \ Maximum Tx packet size \ both?
Is it include L2\L3 headers? Vlan?
How is it going together with ``uint32_t max_lro_pkt_size``?

Also when should the user configure DEV_RX_OFFLOAD_SCATTER?

Matan

From: Ferruh Yigit
> Signed-off-by: Ferruh Yigit <ferruh.yigit@intel.com>
> Acked-by: Konstantin Ananyev <konstantin.ananyev@intel.com>
> ---
> Cc: Thomas Monjalon <thomas@monjalon.net>
> Cc: Andrew Rybchenko <arybchenko@solarflare.com>
> Cc: Konstantin Ananyev <konstantin.ananyev@intel.com>
> Cc: Matan Azrad <matan@nvidia.com>
> Cc: Olivier Matz <olivier.matz@6wind.com>
> Cc: Jerin Jacob <jerinj@marvell.com>
> 
> v2:
> * ``uint32_t mtu`` moved to ``struct rte_eth_conf``
> * The "Driver is responsible from updating ``(struct
>   rte_eth_dev)->data->mtu``" updated because ethdev layer also can do
>   this. The intention there was both APIs should update the variable.
> 
> Another open question is from Andrew, if we can remove the ``uint32_t
> max_rx_pkt_len`` completely from the ``rte_eth_dev_configure()``.
> This may force applications to have one more additional
> ``rte_eth_dev_set_mtu()`` call for device initialization, but if applications are
> OK with the default values most of times, agree that removing is easier
> solution, please comment.
> ---
>  doc/guides/rel_notes/deprecation.rst | 25 +++++++++++++++++++++++++
>  1 file changed, 25 insertions(+)
> 
> diff --git a/doc/guides/rel_notes/deprecation.rst
> b/doc/guides/rel_notes/deprecation.rst
> index 96986fabd598..73e43581d615 100644
> --- a/doc/guides/rel_notes/deprecation.rst
> +++ b/doc/guides/rel_notes/deprecation.rst
> @@ -88,6 +88,31 @@ Deprecation Notices
>    will be limited to maximum 256 queues.
>    Also compile time flag ``RTE_ETHDEV_QUEUE_STAT_CNTRS`` will be
> removed.
> 
> +* ethdev: ``uint32_t max_rx_pkt_len`` field of ``struct
> +rte_eth_rxmode``, will be
> +  replaced by a new ``uint32_t mtu`` field of ``struct rte_eth_conf`` in v21.11.
> +  The new ``mtu`` field will be used to configure the initial device
> +MTU via
> +  ``rte_eth_dev_configure()`` API.
> +  Later MTU can be changed by ``rte_eth_dev_set_mtu()`` API as done now.
> +  The existing ``(struct rte_eth_dev)->data->mtu`` variable will be
> +used to store
> +  the configured ``mtu`` value,
> +  and this new ``(struct rte_eth_dev)->data->dev_conf.mtu`` variable
> +will
> +  be used to store the user configuration request.
> +  Unlike ``max_rx_pkt_len``, which was valid only when ``JUMBO_FRAME``
> +enabled,
> +  ``mtu`` field will be always valid.
> +  When ``mtu`` config is not provided by the application, default
> +``RTE_ETHER_MTU``
> +  value will be used.
> +  ``(struct rte_eth_dev)->data->mtu`` should be updated after MTU set
> +successfully,
> +  either by ``rte_eth_dev_configure()`` or ``rte_eth_dev_set_mtu()``.
> +
> +  An application may need to configure device for a specific Rx packet
> + size, like for  cases ``DEV_RX_OFFLOAD_SCATTER`` is not supported and
> + device received packet size  can't be bigger than Rx buffer size.
> +  To cover these cases an application needs to know the device packet
> + overhead to be  able to calculate the ``mtu`` corresponding to a Rx
> + buffer size, for this  ``(struct rte_eth_dev_info).max_rx_pktlen``
> + will be kept,  the device packet overhead can be calculated as:
> +  ``(struct rte_eth_dev_info).max_rx_pktlen - (struct
> + rte_eth_dev_info).max_mtu``
> +
>  * sched: To allow more traffic classes, flexible mapping of pipe queues to
>    traffic classes, and subport level configuration of pipes and queues
>    changes will be made to macros, data structures and API functions defined
> --
> 2.26.2