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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 >>>>>>> Signed-off-by: Andrew Rybchenko >>>>>>> Reviewed-by: Andy Moreton >>>>>>> --- >>>>>>> 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'. 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()'. >>> The patch does not change external API, does not change etcdev >>> bahaviour. It just clarify requirements on driver ops to >>> allow to check less in all drivers and support less cases >>> in all drivers. >>> >> >> It is not clarifying the requirements of dev_ops, but changing it. Previously >> there was nothing saying only one of the '_by_id' dev_ops should support >> returning element count. > > I say "clarifying" since I adjust it a real source of > truth for internals - implementation, usage of these > callback by ethdev layer. > > Yes, I agree that it changes documentation. > >> >>> If we make a one more step back, frankly speaking I think we >>> have too many functions to retrieve statistics. I can >>> understand from ethdev API point of view taking API stability >>> into account etc. But why do we have so many complicated >>> driver callbacks? >>>> First of all I'd like to do one more cleanup: >>> change eth_xstats_get_names_by_id_t prototype to >>> have ids before xstats_names. >>> I.e. eth_xstats_get_by_id_t(dev, ids, values, size) >>> eth_xstats_get_names_by_id_t(dev, ids, names, size) >>> >> >> +1 > > See patch 3/4 in v6 > >> >>> Second, merge eth_xstats_get_names_t and eth_xstats_get_names_by_id_t >>> callbacks to keep >>> name of the first, but prototype from the second. >>> The reason is equal functionality if ids==NULL, >>> shorter name of the first and optional ids (i.e. no >>> reason to mention optional parameter in name). >>> Drivers which do not implement by_id_t, >>> but implement eth_xstats_get_names_t, will simply >>> return ENOTSUP if ids!=NULL. >>> >> >> No objection, _by_id() version is already superset of the other. > > See patch 4/4 in v6 > >> >>> The case of values ops is more complicated, >>> however since: >>> >>> 2834 * There is an assumption that 'xstat_names' and 'xstats' arrays >>> are matched >>> 2835 * by array index: >>> 2836 * xstats_names[i].name => xstats[i].value >>> 2837 * >>> 2838 * And the array index is same with id field of 'struct rte_eth_xstat': >>> 2839 * xstats[i].id == i >>> 2840 * >>> 2841 * This assumption makes key-value pair matching less flexible but >>> simpler. >>> >>> we can switch to eth_xstats_get_by_id_t only callback as >>> well and fill in stats->id equal to index on ethdev layer. >> >> When ids != NULL, the index from 'ids' can be used, isn't it. > > Yes, of course, but above documentation is for API without IDs. > >> >>> However, it will require extra buffer for >>> uint64_t *values and copying in the rte_eth_xstats_get() >>> implementation. So, I doubt in this case. >>> >> >> Overall merging xstats _by_id APIs doesn't look bad idea, but since it will >> require change in applications, I am not really sure if benefit worth the >> trouble it brings to users. > > Yes, I agree. I'm not going to change external API. > >>> In fact, it is sad that we still do not move forward >>> in accordance with Thomas presentation made 2 years ago. >>> >> >> In my experience things don't move forward without proper plan (who, what, when). >> > > +1 >