Re: [PATCH v5 2/2] ethdev: support xstats reset telemetry command

[fengchengwen <fengchengwen@huawei.com>]

On 2023/2/20 21:05, Thomas Monjalon wrote:
> 17/02/2023 10:44, fengchengwen:
>> On 2023/2/16 20:54, Bruce Richardson wrote:
>>> On Thu, Feb 16, 2023 at 08:42:34PM +0800, fengchengwen wrote:
>>>> On 2023/2/16 20:06, Ferruh Yigit wrote:
>>>>> On 2/16/2023 11:53 AM, fengchengwen wrote:
>>>>>> On 2023/2/15 11:19, Dongdong Liu wrote:
>>>>>>> Hi Chengwen
>>>>>>>
>>>>>>> On 2023/2/9 10:32, Chengwen Feng wrote:
>>>>>>>> The xstats reset is useful for debugging, so add it to the ethdev
>>>>>>>> telemetry command lists.
>>>>>>>>
>>>>>>>> Signed-off-by: Chengwen Feng <fengchengwen@huawei.com>
>>>>>>> This patch looks good, so
>>>>>>> Reviewed-by: Dongdong Liu <liudongdong3@huawei.com>
>>>>>>>
>>>>>>> A minior question
>>>>>>> Do we need to support stats reset ?
>>>>>>
>>>>>> Stats is contained by xstats, and future direction I think is xstats.
>>>>>> So I think we don't need support stats reset.
>>>>>>
>>>>>
>>>>> I have similar question with Dongdong, readonly values are safe for
>>>>> telemetry, but modifying data can be more tricky since we don't have
>>>>> locking in ethdev APIs, this can cause concurrency issues.
>>>>
>>>> Yes, it indeed has concurrency issues.
>>>>
>>>>>
>>>>> Overall do we want telemetry go that way and become something that
>>>>> alters ethdev data/config?
>>>>
>>>> There are at least two part of data: config and status.
>>>> For stats (which belong status data) could help for debugging, I think it's acceptable.
>>>>
>>>> As for concurrency issues. People should know what to do and when to do, just like
>>>> the don't invoke config API (e.g. dev_configure/dev_start/...) concurrency.
>>>>
>>> While this is probably ok for now, I think in next release we should look
>>> to add some sort of support for locking for destructive ops in a future
>>> release. For example, we could:
>>>
>>> 1. Add support for marking a callback as "destructive" and only allow it to
>>> be called if only one connection is present or
>>>
>>> 2. Make it possible for callbacks to query the number of connections so
>>> that the callback itself is non-destructive in more than one connection is
>>> open.
>>>
>>> [Both of these will require locking support so that new connections aren't
>>> openned when the callback is in-flight!]
>>
>> Except telemetry, the application may have other console could execute DPDK API.
>> So I think trying to keep it simple, it's up to the user to invoke.
> 
> No, the user should not be responsible for concurrency issues.
> We can ask the app developper to take care,
> but not to the user who has no control on what happens in the app.
> 
> On a more general note, I feel the expansion of telemetry is not controlled enough.
> I would like to stop on adding more telemetry until we have a clear guideline
> about what is telemetry for and how to use it.

Hi Thomas,

Should this be discussed on TB?

Thanks.

> 
> 
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