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

[Ferruh Yigit]

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 at 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 at dpdk.org
>>>
>>> Signed-off-by: Ivan Ilchenko <ivan.ilchenko at oktetlabs.ru>
>>> Signed-off-by: Andrew Rybchenko <andrew.rybchenko at oktetlabs.ru>
>>> Reviewed-by: Andy Moreton <amoreton at 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.