Re: [PATCH v1 3/5] ethdev: add API for direct rearm mode

[Andrew Rybchenko <andrew.rybchenko@oktetlabs.ru>]

On 5/11/22 01:49, Honnappa Nagarahalli wrote:
>>> On 4/20/22 11:16, Feifei Wang wrote:
>>>> Add API for enabling direct rearm mode and for mapping RX and TX
>>>> queues. Currently, the API supports 1:1(txq : rxq) mapping.
>>>>
>>>> Suggested-by: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>
>>>> Signed-off-by: Feifei Wang <feifei.wang2@arm.com>
>>>> Reviewed-by: Ruifeng Wang <ruifeng.wang@arm.com>
>>>> Reviewed-by: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>
>>>> +	(*dev->dev_ops->rx_queue_direct_rearm_enable)(dev,
>>> rx_queue_id);
>>>> +	(*dev->dev_ops->rx_queue_direct_rearm_map)(dev, rx_queue_id,
>>>> +			tx_port_id, tx_queue_id);
>>>
>>> We must check that function pointers are not NULL as usual.
>>> Return values must be checked.
>> [Feifei] I agree with this, The check for pointer and return value will be added
>>
>>> Isn't is safe to setup map and than enable.
>>> Otherwise we definitely need disable.
>> [Feifei] I will change code that map first and then set 'rxq->offload' to enable
>> direct-rearm mode.
>>
>>> Also, what should happen on Tx port unplug? How to continue if we
>>> still have Rx port up and running?
>> [Feifei] For direct rearm mode, if Tx port unplug, it means there is no buffer
>> from Tx.
>> And then, Rx will put buffer from mempool as usual for rearm.
> Andrew, when you say 'TX port unplug', do you mean the 'rte_eth_dev_tx_queue_stop' is called? Is calling 'rte_eth_dev_tx_queue_stop' allowed when the device is running?

I think that deferred start and presence of
rte_eth_dev_tx_queue_stop() implies the possibility to stop
Tx queue. But, yes, application should care about conditions
to have no traffic running to Tx queue.

Anyway, I was talking about hot unplug of the entire
device used as Tx port in above config.