[dpdk-dev] [PATCH 1/6] ethdev: add descriptor status API

Andrew Rybchenko arybchenko at solarflare.com
Thu Mar 2 16:05:52 CET 2017


On 03/02/2017 05:54 PM, Olivier Matz wrote:
>>>>> + *
>>>>> + * @param port_id
>>>>> + *  The port identifier of the Ethernet device.
>>>>> + * @param queue_id
>>>>> + *  The Rx queue identifier on this port.
>>>>> + * @param offset
>>>>> + *  The offset of the descriptor starting from tail (0 is the next
>>>>> + *  packet to be received by the driver).
>>>>> + * @return
>>>>> + *  - (RTE_ETH_DESC_AVAIL): Descriptor is available for the hardware to
>>>>> + *    receive a packet.
>>>>> + *  - (RTE_ETH_DESC_DONE): Descriptor is done, it is filled by hw, but
>>>>> + *    not yet processed by the driver (i.e. in the receive queue).
>>>>> + *  - (RTE_ETH_DESC_USED): Descriptor is unavailable (hold by driver,
>>>>> + *    not yet returned to hw).
>>>> It looks like it is the most suitable for descriptors which are reserved
>>>> and never used.
>>> Can you give some more details about what is a reserved but never
>>> used descriptor? (same question for Tx)
>> Our HW has a requirement to keep few descriptors always unused (i.e.
>> some gap between tail and head). It is just a few descriptors, but
>> invalid descriptor status may misguide application. E.g. if Rx queue
>> size is 512 and offset 510, it will always be unused (since it is
>> reserved). It is not an indication that core is too slow and can't keep
>> the pace.
> Understood.
>
> I can change _USED into _UNAVAIL (add it for Tx), with the following
> description:
>
> - (RTE_ETH_DESC_UNAVAIL): Descriptor is unavailable: either hold by driver
>    and not yet returned to hw, or reserved by the hardware.

Looks good. Do I understand correctly that it will be reported for 
descriptors which are not refilled (posted to HW) because of rx_free_thresh?



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