Re: [PATCH] ethdev: add dump regs for telemetry

[Ferruh Yigit <ferruh.yigit@amd.com>]

On 1/10/2024 2:09 PM, Thomas Monjalon wrote:
> 10/01/2024 13:15, Ferruh Yigit:
>> On 1/10/2024 1:38 AM, fengchengwen wrote:
>>> Hi Ferruh,
>>>
>>> On 2024/1/10 2:06, Ferruh Yigit wrote:
>>>> On 1/9/2024 2:19 AM, Jie Hai wrote:
>>>>> On 2023/12/14 20:49, Ferruh Yigit wrote:
>>>>>> On 12/14/2023 1:56 AM, Jie Hai wrote:
>>>>>>> The ethdev library now registers a telemetry command for
>>>>>>> dump regs.
>>>>>>>
>>>>>>> An example usage is shown below:
>>>>>>> --> /ethdev/regs,test
>>>>>>> {
>>>>>>>    "/ethdev/regs": {
>>>>>>>      "regs_offset": 0,
>>>>>>>      "regs_length": 3192,
>>>>>>>      "regs_width": 4,
>>>>>>>      "device_version": "0x1080f00",
>>>>>>>      "regs_file": "port_0_regs_test"
>>>>>>>    }
>>>>>>> }
>>>>>
>>>>>>
>>>>>> Above code writes register data to a file.
>>>>>>
>>>>>> I am not sure about this kind of usage of telemetry command, that it
>>>>>> cause data to be written to a file.
>>>>>>
>>>>>> My understanding is, telemetry usage is based on what telemetry client
>>>>>> receives.
>>>>>> What do you think just keep the 'reg_info' fields excluding data to the
>>>>>> file?
>>>>>>
>>>>>> .Hi, Ferruh
>>>>>
>>>>> I tried to write all register information to telemetry data,
>>>>> but gave up because some drivers had too many registers (eg.ixgbe)
>>>>> to carry. Therefore, the writing data to file approach is selected.
>>>>>
>>>>> When we query a register, the register content is the key.
>>>>> The information such as the width and length is only auxiliary
>>>>> information. If the register data cannot be obtained, the auxiliary
>>>>> information is optional. So I don't think register data should be removed.
>>>>>
>>>>> In my opinion, writing a file is a more appropriate way to do it.
>>>>> I wonder if there's a better way.
>>>>>
>>>>>
>>>>
>>>> Is there a usecase to get register information from telemetry interface?
>>>
>>> Among the available tools:
>>> 1, ethtool/proc-info: should use multi-process mechanism to connect to the main process
>>> 2, telemetry: easier, lighter load, and it don't need re-probe the ethdev in the secondary process,
>>>               and also cost more resource, like hugepage, cores.
>>>
>>> From our users, they prefer use the second 'telemetry', so I think we should move
>>> more status-query-points to telemetry.
>>>
>>> As for this question, I think it's okay to get register info from telemetry.
>>>
>>>
>>>
>>> Another question, we have some internal registers, which:
>>> 1. Is not suitable expose by xstats, because they may includes configuration
>>> 2. Is not suitable expose by dumps, because this dumps is hard to understand (because it only has value).
>>>
>>> So we plan to add some telemetry points in the driver itself, so we could display them like xstats:
>>> "xxxx" : 0x1234
>>> "yyyy" : 0x100
>>>
>>> Will the community accept this kind of telemetry points which limit one driver ?
>>>
>>
>> Hi Chengwen,
>>
>> I see there is a usecase/requirement.
>>
>> With this patch, even using file, only register values are dumped and
>> isn't it hard to find value of specific register?
>>
>> ("xxxx" : 0x1234) approach looks better, but instead of making this
>> telemetry support for specific driver, what about making it in two steps.
>>
>> First add new dev_ops, (or update existing one), to get registers with
>> "name: value" format, (in a way to allow empty name), or even perhaps
>> "name: offset, value" format.
> 
> I'm OK to add an API for dumping registers, and guess what?
> We already have it: rte_eth_dev_get_reg_info().
> We may extend it to query a subset of registers.
> 

This patch already using 'rte_eth_dev_get_reg_info()', but issue is how
it is used, it gets filename from telemetry and dumps registers to that
file.

>> And in second stage add telemetry support around it.
>> (Name being optional lets us wrap exiting 'get_reg' dev_ops with new one)
> 
> I am against overloading telemetry for debug purpose.
> 

Reading some registers can be debugging or monitoring, I believe it is
in the gray area.

>> When adding dev_ops, it may get an additional 'filter' parameter, to get
>> only subset of regs, like "mac*" to get regs name staring with "mac",
>> this may help for the cases there are too many registers you mentioned.
>>
>> Anyway, we can discuss more about its design, but what do you think
>> about first having a dev_ops for this?
> 
> 
>