Re: [dpdk-dev] [dpdk-stable] [PATCH v5 2/2] ethdev: fix docs of drivers callbacks getting xstats by IDs

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

On 9/30/21 6:30 PM, Ferruh Yigit wrote:
> On 9/30/2021 3:01 PM, Andrew Rybchenko wrote:
>> On 9/30/21 3:08 PM, Ferruh Yigit wrote:
>>> On 9/29/2021 12:54 PM, Andrew Rybchenko wrote:
>>>> On 9/29/21 11:44 AM, Ferruh Yigit wrote:
>>>>> On 9/28/2021 5:53 PM, Andrew Rybchenko wrote:
>>>>>> On 9/28/21 7:50 PM, Ferruh Yigit wrote:
>>>>>>> On 9/28/2021 1:05 PM, Andrew Rybchenko wrote:
>>>>>>>> From: Ivan Ilchenko <ivan.ilchenko@oktetlabs.ru>
>>>>>>>>
>>>>>>>> Update xstats by IDs callbacks documentation in accordance with
>>>>>>>> ethdev usage of these callbacks. Document valid combinations of
>>>>>>>> input arguments to make driver implementation simpler.
>>>>>>>>
>>>>>>>> Fixes: 79c913a42f0 ("ethdev: retrieve xstats by ID")
>>>>>>>> Cc: stable@dpdk.org
>>>>>>>>
>>>>>>>> Signed-off-by: Ivan Ilchenko <ivan.ilchenko@oktetlabs.ru>
>>>>>>>> Signed-off-by: Andrew Rybchenko <andrew.rybchenko@oktetlabs.ru>
>>>>>>>> Reviewed-by: Andy Moreton <amoreton@xilinx.com>
>>>>>>>> ---
>>>>>>>>  lib/ethdev/ethdev_driver.h | 42 ++++++++++++++++++++++++++++++++++++--
>>>>>>>>  1 file changed, 40 insertions(+), 2 deletions(-)
>>>>>>>>
>>>>>>>> diff --git a/lib/ethdev/ethdev_driver.h b/lib/ethdev/ethdev_driver.h
>>>>>>>> index 40e474aa7e..c89eefcc42 100644
>>>>>>>> --- a/lib/ethdev/ethdev_driver.h
>>>>>>>> +++ b/lib/ethdev/ethdev_driver.h
>>>>>>>> @@ -187,11 +187,28 @@ typedef int (*eth_xstats_get_t)(struct rte_eth_dev *dev,
>>>>>>>>  	struct rte_eth_xstat *stats, unsigned int n);
>>>>>>>>  /**< @internal Get extended stats of an Ethernet device. */
>>>>>>>>  
>>>>>>>> +/**
>>>>>>>> + * @internal
>>>>>>>> + * Get extended stats of an Ethernet device.
>>>>>>>> + *
>>>>>>>> + * @param dev
>>>>>>>> + *   ethdev handle of port.
>>>>>>>> + * @param ids
>>>>>>>> + *   IDs array to retrieve specific statistics. Must not be NULL.
>>>>>>>> + * @param values
>>>>>>>> + *   A pointer to a table to be filled with device statistics values.
>>>>>>>> + *   Must not be NULL.
>>>>>>>> + * @param n
>>>>>>>> + *   Element count in @p ids and @p values.
>>>>>>>> + *
>>>>>>>> + * @return
>>>>>>>> + *   - A number of filled in stats.
>>>>>>>> + *   - A negative value on error.
>>>>>>>> + */
>>>>>>>>  typedef int (*eth_xstats_get_by_id_t)(struct rte_eth_dev *dev,
>>>>>>>>  				      const uint64_t *ids,
>>>>>>>>  				      uint64_t *values,
>>>>>>>>  				      unsigned int n);
>>>>>>>> -/**< @internal Get extended stats of an Ethernet device. */
>>>>>>>>  
>>>>>>>>  /**
>>>>>>>>   * @internal
>>>>>>>> @@ -218,10 +235,31 @@ typedef int (*eth_xstats_get_names_t)(struct rte_eth_dev *dev,
>>>>>>>>  	struct rte_eth_xstat_name *xstats_names, unsigned int size);
>>>>>>>>  /**< @internal Get names of extended stats of an Ethernet device. */
>>>>>>>>  
>>>>>>>> +/**
>>>>>>>> + * @internal
>>>>>>>> + * Get names of extended stats of an Ethernet device.
>>>>>>>> + * For name count, set @p xstats_names and @p ids to NULL.
>>>>>>>
>>>>>>> Why limiting this behavior to 'xstats_get_names_by_id'?
>>>>>>>
>>>>>>> Internally 'xstats_get_names_by_id' is used to get the count, but I think this
>>>>>>> is not intentionally selected, just one of the xstats_*_by_id dev_ops used.
>>>>>>>
>>>>>>> I think it is confusing to have this support for one of the '_by_id' dev_ops but
>>>>>>> not for other. Why not require both to support returning 'count'?
>>>>>>
>>>>>> Simply because it is dead code. There is no point to require
>>>>>> from driver to have dead code.
>>>>>>
>>>>>
>>>>> Let me step back a little, both ethdev APIs can be used to return xstats count
>>>>> by providing 'values/names' & 'ids' pointers as NULL and 'size' as 0:
>>>>> 'rte_eth_xstats_get_names_by_id()'
>>>>> 'rte_eth_xstats_get_by_id()'
>>>>>
>>>>> But internally both APIs use 'xstats_get_names_by_id' dev_ops to get the count,
>>>>> as said above I believe this selection is done unintentionally.
>>>>>
>>>>>
>>>>> I am for below two options:
>>>>>
>>>>> a) Internally use 'xstats_get_names' || 'xstats_get' dev_ops to get the xstats
>>>>> count, and doesn't support getting xstats count for both '_by_id' dev_ops, this
>>>>> simplifies driver code. As far as I remember I suggested this before, still I
>>>>> prefer this one.
>>>>>
>>>>> b) If we will support getting xstats count from '_by_id' dev_ops, I think both
>>>>> should support it, to not make it more complex to figure out which one support
>>>>> what. As sample both 'xstats_get_names' and 'xstats_get' supports getting xstats
>>>>> count, not just one.
>>>>>
>>>>
>>>> In (b) do you suggest to change ethdev to use xstats_get_by_id
>>>> driver op if users asks for a number of xstats using
>>>> rte_eth_xstats_get_by_id()? It will complicate ethdev and
>>>> will complicate drivers. Just for the symmetry?
>>>>
>>>
>>> Not just for symmetry, but simplify the logic. Both dev_ops are very similar and
>>
>> I'm sorry, but could you point of which logic you'd
>> like to simply. Less requirements on driver ops
>> means less code required inside.
>>
>>> they are having different behavior with same parameters is confusing.
>>
>> Ah, logic from PMD maintainer point of view. Does it
>> really worse to require extra code inside because of it?
>>
>>> If you want to simplify the drivers why not go with option (a)? Option (a) also
>>> doesn't change external API, and has only minor change in the ethdev layer.
>>
>> Is two extra patches in v6 (discussed below) a step
>> towards (a)?
>>
> 
> I am not sure of it, for (a) ethdev layer will handle getting all stats or
> getting count using 'xstats_get_names' || 'xstats_get', and '*_by_id()' dev_ops
> will become simpler since they won't accept NULL 'ids' & 'values'.

Got it. Will fix it in v7. I'll remove requirement in a
dedicated patch, but may be it should be squashed with
this one on apply.

> Also when dev_ops merged, it forces PMDs to implement the getting by ids, but
> now it is covered by ethdev layer for the PMDs that doesn't implement '_by_id()'.

Thanks, good catch. I'll handle it v7 as well.