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

["Joseph, Anoob" <Anoob.Joseph@caviumnetworks.com>]

Hi Declan,

Please see inline.

Thanks,

Anoob


On 26-06-2018 15:42, Doherty, Declan wrote:
> External Email
>
> 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.
In rte_mbuf.h, the minimum size required for packets involved in rx/tx 
is specified and that considers headroom also. Applications usually use 
these default macros while creating mbufs which are involved in rx/tx.
https://git.dpdk.org/dpdk/tree/lib/librte_mbuf/rte_mbuf.h#n411
>
>> 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?
It is purely per device basis. The device can specify upper bounds for 
the head/tailroom. A device that even specified the room, may not even 
use the entire room in all cases. So it doesn't have to be algo specific.
>
>> 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. */
>>
>