[dpdk-dev] [dpdk-techboard] [PATCH V5 1/2] dpdk: resolve compiling errors for per-queue stats

[Ferruh Yigit]

On 10/6/2020 9:33 AM, Olivier Matz wrote:
> Hi,
> 
> On Mon, Oct 05, 2020 at 01:23:08PM +0100, Ferruh Yigit wrote:
>> On 9/28/2020 4:43 PM, Stephen Hemminger wrote:
>>> On Mon, 28 Sep 2020 17:24:26 +0200
>>> Thomas Monjalon <thomas at monjalon.net> wrote:
>>>
>>>> 28/09/2020 15:53, Ferruh Yigit:
>>>>> On 9/28/2020 10:16 AM, Thomas Monjalon wrote:
>>>>>> 28/09/2020 10:59, Ferruh Yigit:
>>>>>>> On 9/27/2020 4:16 AM, Min Hu (Connor) wrote:
>>>>>>>> From: Huisong Li <lihuisong at huawei.com>
>>>>>>>>
>>>>>>>> Currently, only statistics of rx/tx queues with queue_id less than
>>>>>>>> RTE_ETHDEV_QUEUE_STAT_CNTRS can be displayed. If there is a certain
>>>>>>>> application scenario that it needs to use 256 or more than 256 queues
>>>>>>>> and display all statistics of rx/tx queue. At this moment, we have to
>>>>>>>> change the macro to be equaled to the queue number.
>>>>>>>>
>>>>>>>> However, modifying the macro to be greater than 256 will trigger
>>>>>>>> many errors and warnings from test-pmd, PMD drivers and librte_ethdev
>>>>>>>> during compiling dpdk project. But it is possible and permitted that
>>>>>>>> rx/tx queue number is greater than 256 and all statistics of rx/tx
>>>>>>>> queue need to be displayed. In addition, the data type of rx/tx queue
>>>>>>>> number in rte_eth_dev_configure API is 'uint16_t'. So It is unreasonable
>>>>>>>> to use the 'uint8_t' type for variables that control which per-queue
>>>>>>>> statistics can be displayed.
>>>>>>
>>>>>> The explanation is too much complex and misleading.
>>>>>> You mean you cannot increase RTE_ETHDEV_QUEUE_STAT_CNTRS
>>>>>> above 256 because it is an 8-bit type?
>>>>>>
>>>>>> [...]
>>>>>>>> --- a/lib/librte_ethdev/rte_ethdev.h
>>>>>>>> +++ b/lib/librte_ethdev/rte_ethdev.h
>>>>>>>>      int rte_eth_dev_set_tx_queue_stats_mapping(uint16_t port_id,
>>>>>>>> -		uint16_t tx_queue_id, uint8_t stat_idx);
>>>>>>>> +		uint16_t tx_queue_id, uint16_t stat_idx);
>>>>>> [...]
>>>>>>>>      int rte_eth_dev_set_rx_queue_stats_mapping(uint16_t port_id,
>>>>>>>>      					   uint16_t rx_queue_id,
>>>>>>>> -					   uint8_t stat_idx);
>>>>>>>> +					   uint16_t stat_idx);
>>>>>> [...]
>>>>>>> cc'ed tech-board,
>>>>>>>
>>>>>>> The patch breaks the ethdev ABI without a deprecation notice from previous
>>>>>>> release(s).
>>>>>>>
>>>>>>> It is mainly a fix to the port_id storage type, which we have updated from
>>>>>>> uint8_t to uint16_t in past but some seems remained for
>>>>>>> 'rte_eth_dev_set_tx_queue_stats_mapping()' &
>>>>>>> 'rte_eth_dev_set_rx_queue_stats_mapping()' APIs.
>>>>>>
>>>>>> No, it is not related to the port id, but the number of limited stats.
>>>>>
>>>>> Right, it is not related to the port id, it is fixing the storage type for index
>>>>> used to map the queue stats.
>>>>>>> Since the ethdev library already heavily breaks the ABI this release, I am for
>>>>>>> getting this fix, instead of waiting the fix for one more year.
>>>>>>
>>>>>> If stats can be managed for more than 256 queues, I think it means
>>>>>> it is not limited. In this case, we probably don't need the API
>>>>>> *_queue_stats_mapping which was invented for a limitation of ixgbe.
>>>>>>
>>>>>> The problem is probably somewhere else (in testpmd),
>>>>>> that's why I am against this patch.
>>>>>
>>>>> This patch is not to fix queue stats mapping, I agree there are problems related
>>>>> to it, already shared as comment to this set.
>>>>>
>>>>> But this patch is to fix the build errors when 'RTE_ETHDEV_QUEUE_STAT_CNTRS'
>>>>> needs to set more than 255. Where the build errors seems around the
>>>>> stats_mapping APIs.
>>>>
>>>> It is not said this API is supposed to manage more than 256 queues mapping.
>>>> In general we should not need this API.
>>>> I think it is solving the wrong problem.
>>>
>>>
>>> The original API is a band aid for the limited number of statistics counters
>>> in the Intel IXGBE hardware. It crept into to the DPDK as an API. I would rather
>>> have per-queue statistics and make ixgbe say "not supported"
>>>
>>
>> The current issue is not directly related to '*_queue_stats_mapping' APIs.
>>
>> Problem is not able to set 'RTE_ETHDEV_QUEUE_STAT_CNTRS' > 255.
>> User may need to set the 'RTE_ETHDEV_QUEUE_STAT_CNTRS' > 255, since it is
>> used to define size of the stats counter.
>> "uint64_t q_ipackets[RTE_ETHDEV_QUEUE_STAT_CNTRS];"
>>
>> When 'RTE_ETHDEV_QUEUE_STAT_CNTRS' > 255, it gives multiple build errors,
>> the one in the ethdev is like [1].
>>
>> This can be fixed two ways,
>> a) increase the size of 'stat_idx' storage type to u16 in the
>> '*_queue_stats_mapping' APIs, this is what this patch does.
>> b) Fix with a casting in the comparison, without changing the APIs.
>>
>> I think both are OK, but is (b) more preferable?
> 
> I think the patch (a) is ok, knowing that RTE_ETHDEV_QUEUE_STAT_CNTRS is
> not modified.
> 
> On the substance, I agree with Thomas that the queue_stats_mapping API
> should be replaced by xstats.
> 

This has been discussed in the last technical board meeting, the decision was to 
use xstats to get queue related statistics [2].

But after second look, even if xstats is used to get statistics, 
'RTE_ETHDEV_QUEUE_STAT_CNTRS' is used, since xstats uses 'rte_eth_stats_get()' 
to get queue statistics.
So for the case device has more than 255 queues, 'RTE_ETHDEV_QUEUE_STAT_CNTRS' 
still needs to be set > 255 which will cause the build error.

I have an AR to send a deprecation notice to current method to get the queue 
statistics, and limit the old method to 256 queues. But since xstats is just a 
wrapped to old method, I am not quite sure how deprecating it will work.

@Thomas, @Honnappa, can you give some more insight on the issue?


[2]
https://mails.dpdk.org/archives/dev/2020-October/185299.html

> 
>>
>>
>> [1]
>> ../lib/librte_ethdev/rte_ethdev.c: In function ‘set_queue_stats_mapping’:
>> ../lib/librte_ethdev/rte_ethdev.c:2943:15: warning: comparison is always
>> false due to limited range of data type [-Wtype-limits]
>>   2943 |  if (stat_idx >= RTE_ETHDEV_QUEUE_STAT_CNTRS)
>>        |               ^~