[dpdk-dev] [PATCH v4 2/2] ethdev: get the supported pools for a port

[santosh]

Hi Olivier,


On Friday 29 September 2017 09:32 AM, Olivier MATZ wrote:
> On Mon, Sep 25, 2017 at 10:52:31PM +0100, santosh wrote:
>> Hi Olivier,
>>
>>
>> On Monday 25 September 2017 08:37 AM, Olivier MATZ wrote:
>>
>>>> +{
>>>> +	struct rte_eth_dev *dev;
>>>> +	const char *tmp;
>>>> +
>>>> +	RTE_ETH_VALID_PORTID_OR_ERR_RET(port_id, -ENODEV);
>>>> +
>>>> +	if (pool == NULL)
>>>> +		return -EINVAL;
>>>> +
>>>> +	dev = &rte_eth_devices[port_id];
>>>> +
>>>> +	if (*dev->dev_ops->pools_ops_supported == NULL) {
>>>> +		tmp = rte_eal_mbuf_default_mempool_ops();
>>>> +		if (!strcmp(tmp, pool))
>>>> +			return 0;
>>>> +		else
>>>> +			return -ENOTSUP;
>>> I don't understand why we are comparing with
>>> rte_eal_mbuf_default_mempool_ops().
>>>
>>> It means that the result of the function would be influenced
>>> by the parameter given by the user.
>> But that will be only for ops not supported case and in that case,
>> function _must_ make sure that if inputted param is _default_ops_name
>> then function should return ops supported correct info (whether 
>> returning '0' : Best ops or '1': ops does support 
>> , this part is arguable.. meaning One can say that default_ops ='handle-name' is best possible handle Or 
>> one of handle which platform supports).
>>
>>> I think that a PMD that does not implement ->pools_ops_supported
>>> should always return 1 (mempool is supported).
> I don't agree.
> The result of this API (mempool ops supported or not by a PMD)
> should not depend on what user asks for.
>
>> Return 1 says: PMD support this ops.. 
>>
>> So if ops is not supported and func returns with 1, then which ops application will use?
>> If that ops is default_ops.. then How application will distinguish when to use default ops or
>> param ops?.. as because in both cases func will return with value 1.
>>
>> The approach in the patch takes care of that condition and func will return -ENOTSUP 
>> if (ops not support || inputted param not matching with default ops) otherwise will return
>> 0 or 1.
>>
>> At application side; 
>> For error case: In case of -ENOTSUP, its upto application to use _default_ops or exit.
>> For good case: 0 or 1 case, func gaurantee that handle is either best handle for pool or pool supports
>> that handle.. However in your suggestion if ops not supported case returns 1 then application is not 
>> sure which ops to use.. default_ops Or input ops given to func.
>>
>> make sense? 
> My proposition is:
>
> - what a PMD returns does not depend on used parameter:
>   - 0: best support
>   - 1: support
>   - -ENOTSUP: not supported
>
> - if a PMD does not implement the _ops_supported() API, assume all pools
>   are supported (returns 1)

If API returns 1 for PMD does not implement _ops_supported() case,
then do we really need -ENOTSUP?

If so then in which case API will return -ENOTSUP error, wondering.

> - if the user does not pass a specific mempool ops, the application asks
>   the PMDs, finds the best mempool ops, and use it. This could even be
>   done in rte_pktmbuf_pool_create() as discussed at the summit.

Right.

> - if the user passes a specific mempool ops, we don't need to call the
>   _ops_supported() api, we just try to use this pool.
>
>
> The _ops_supported() returns a property of a PMD, in my opinion it
> should not be impacted by a user argument.
>
Thanks.