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

[fengchengwen <fengchengwen@huawei.com>]

Hi Ferruh,

On 2024/1/11 19:11, Ferruh Yigit wrote:
> On 1/11/2024 1:55 AM, fengchengwen wrote:
>> Hi Ferruh,
>>
>> On 2024/1/10 20:15, Ferruh Yigit wrote:
>>> 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.
>>> And in second stage add telemetry support around it.
>>> (Name being optional lets us wrap exiting 'get_reg' dev_ops with new one)
>>>
>>> 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?
>>
>> I prefer extend struct rte_dev_reg_info, like this:
>>
>> struct rte_eth_reg_name {
>> 	char name[RTE_ETH_REG_NAME_SIZE];
>> };
>>
>> struct rte_dev_reg_info {
>> 	void *data; /**< Buffer for return registers */
>> 	uint32_t offset; /**< Start register table location for access */
>> 	uint32_t length; /**< Number of registers to fetch */
>> 	uint32_t width; /**< Size of device register */
>> 	uint32_t version; /**< Device version */
>> /* Note: below two fields are new added. */
>> 	char *filter; /**< Filter for target subset of registers. This field could affects register selection for data/length/name.  */
>> 	struct rte_eth_reg_name *names; /**< Registers name saver. */
>> };
>>
> 
> ack
> 
>> For driver which don't identify the new filter and names fields:
>>   1. .get_reg return the all registers value.
>>
> 
> ack
> 
> 
>>   2. and driver will not touch the name fields.
>>   3. rte_eth_dev_get_reg_info() could detect name fileds not filled, and then it fill with default names, e.g. offset-1/offset-2/...
>>
> 
> Is there a benefit to provide default names? API can clear the 'names'
> buffer, and driver may or may not fill it. If names not filled, API
> behaves like existing one, it will just provide register values.

ok

> 
> 
>> For driver which identify the new filter and names fields:
>>   1. rte_eth_dev_get_reg_info() will return filtered register's value and also their names.
>>
> 
> ack
> 
>> So that those which invoke rte_eth_dev_get_reg_info() could extra prepare names, and it call the same API will get data and name.
>>
>>
>> Add one new .get_reg_name ops and corresponding API like: rte_eth_dev_get_reg_name() could also feasible.
>> But I think the rte_eth_dev_get_reg_info()'s name is too broad, the info could includes value and also it's name.
>> So I prefer not add one new ops.
>>
> 
> ack
> 
>>
>> Another question? what are the supported values of filters ?
>> I prefer report by dev_info ops, something like a string array end with NULL.
>> Use could query from rte_eth_dev_info_get API.
>>
> 
> I don't think there is a need to populate predefined filter list, it can
> be free text with simple '*' and '.' wildcard support and ',' to support
> list of text.
> 
> User may get full list first, later can filter the ones they are interested.
> Like: "*mac*,*rss*" can match all register names that has 'mac' and
> 'rss' in it.

ok.

Our team will send v1 ASAP.

Thanks.

> 
> .
>