[dpdk-dev] [RFC PATCH 4/4] ethdev: add helpers to move to the new offloads API

[Ferruh Yigit]

On 8/25/2017 2:26 PM, Thomas Monjalon wrote:
> 24/08/2017 09:12, Shahaf Shuler:
>> Thursday, August 24, 2017 1:06 AM, Thomas Monjalon:
>>> 23/08/2017 15:13, Shahaf Shuler:
>>>> Wednesday, August 23, 2017 3:29 PM, Ananyev, Konstantin:
>>>>> From: Shahaf Shuler
>>>>>> In order to enable PMDs to support only one of the APIs, and
>>>>>> applications to avoid branching according to the underlying device
>>>>>> a copy functions to/from the old/new APIs were added.
>>>
>>> Looks a good intent.
>>> I would prefer the word "convert" instead of "copy".
>>>
>>>>>>  int
>>>>>>  rte_eth_rx_queue_setup(uint8_t port_id, uint16_t rx_queue_id,
>>> [...]
>>>>>> +	} else if ((!(dev->data->dev_flags & RTE_ETH_DEV_RXQ_OFFLOAD)) &&
>>>>>> +		   (dev->data->dev_conf.rxmode.ignore == 1)) {
>>>>>> +		int ret;
>>>>>> +		struct rte_eth_rxmode rxmode;
>>>>>> +
>>>>>> +		rte_eth_copy_rxq_offloads(&rxmode, rx_conf);
>>>>>> +		if (memcmp(&rxmode, &dev->data->dev_conf.rxmode,
>>>>>> +			   sizeof(rxmode))) {
>>>>>> +			/*
>>>>>> +			 * device which work with rxmode offloads API requires
>>>>>> +			 * a re-configuration in order to apply the new offloads
>>>>>> +			 * configuration.
>>>>>> +			 */
>>>>>> +			dev->data->dev_conf.rxmode = rxmode;
>>>>>> +			ret = rte_eth_dev_configure(port_id,
>>>>>> +					dev->data->nb_rx_queues,
>>>>>> +					dev->data->nb_tx_queues,
>>>>>> +					&dev->data->dev_conf);
>>>>>
>>>>> Hmm, and why we would need to reconfigure our device in the middle
>>>>> of rx queue setup?
>>>>
>>>> The reason is the old Rx offloads API is configured on device configure.
>>>> This if section is for applications which already moved to the new
>>>> offload API however the underlying PMD still uses the old one.
>>>
>>> Isn't it risky to re-run configure here?
>>> We could also declare this case as an error.
>>>
>>> I think applications which have migrated to the new API, could use the
>>> convert functions themselves before calling configure to support not
>>> migrated PMDs.
>>> The cons of my solution are:
>>> - discourage apps to migrate before all PMDs have migrated
>>> - expose a temporary function to convert API I propose it anyway because
>>> there is always someone to like bad ideas ;)
>>
>> Yes. I tried to make it as simple as possible for application to move to the new API.
>> Defining it as error flow, will enforce the application to check the PMD offload mode and branch accordingly. The conversion functions are a good helpers, yet the code remains complex due to the different cases with the different PMDs.
>>
>> Considering the re-configuration is risky, and without other ideas I will need to fall back to the error flow case.
>> Are we OK with that?
> 
> I think we can take the risk of keeping this call to
> rte_eth_dev_configure() in the middle of rte_eth_rx_queue_setup().
> In theory it should be acceptable.
> If we merge it soon, it can be better tested with every drivers.

I doubt about taking that risk. Some driver does HW configuration via
configure() and combination of start/stop, setup_queue and configure can
be complex.

I am for generating error for this case.

Generating error also can be good motivation for PMDs to adapt new method.