Re: [dpdk-dev] [PATCH 1/2] cryptodev: add min headroom and tailroom requirement

["Doherty, Declan" <declan.doherty@intel.com>]

On 19/06/2018 7:26 AM, Anoob Joseph wrote:
> Enabling crypto devs to specify the minimum headroom and tailroom it
> expects in the mbuf. For net PMDs, standard headroom has to be honoured
> by applications, which is not strictly followed for crypto devs. This

How is this done for NET PMDs, I don't see anything explicit in the 
ehtdev API for specification of headroom requirements.

> prevents crypto devs from using free space in mbuf (available as
> head/tailroom) for internal requirements in crypto operations. Addition
> of head/tailroom requirement will help PMDs to communicate such
> requirements to the application.
> 
> The availability and use of head/tailroom is an optimization if the
> hardware supports use of head/tailroom for crypto-op info. For devices
> that do not support using the head/tailroom, they can continue to operate
> without any performance-drop.
> 
Is there any variations in requirements for terms headroom/tailroom on a 
per algorithmic basis or is it purely for the device?

> Signed-off-by: Anoob Joseph <anoob.joseph@caviumnetworks.com>
> ---
>   doc/guides/rel_notes/deprecation.rst | 4 ++++
>   lib/librte_cryptodev/rte_cryptodev.h | 6 ++++++
>   2 files changed, 10 insertions(+)
> 
> diff --git a/doc/guides/rel_notes/deprecation.rst b/doc/guides/rel_notes/deprecation.rst
> index 1ce692e..a547289 100644
> --- a/doc/guides/rel_notes/deprecation.rst
> +++ b/doc/guides/rel_notes/deprecation.rst
> @@ -122,3 +122,7 @@ Deprecation Notices
>     - Function ``rte_cryptodev_get_private_session_size()`` will be deprecated
>       in 18.05, and it gets replaced with ``rte_cryptodev_sym_get_private_session_size()``.
>       It will be removed in 18.08.
> +  - New field, ``min_headroom_req``, added in ``rte_cryptodev_info`` structure. It will be
> +    added in 18.11.
> +  - New field, ``min_tailroom_req``, added in ``rte_cryptodev_info`` structure. It will be
> +    added in 18.11.
> diff --git a/lib/librte_cryptodev/rte_cryptodev.h b/lib/librte_cryptodev/rte_cryptodev.h
> index 92ce6d4..fa944b8 100644
> --- a/lib/librte_cryptodev/rte_cryptodev.h
> +++ b/lib/librte_cryptodev/rte_cryptodev.h
> @@ -382,6 +382,12 @@ struct rte_cryptodev_info {
>   	unsigned max_nb_queue_pairs;
>   	/**< Maximum number of queues pairs supported by device. */
>   
> +	uint32_t min_headroom_req;
> +	/**< Minimum mbuf headroom required by device */
> +
> +	uint32_t min_tailroom_req;
> +	/**< Minimum mbuf tailroom required by device */
> +
>   	struct {
>   		unsigned max_nb_sessions;
>   		/**< Maximum number of sessions supported by device. */
>