Re: [PATCH] net/mana: use RTE_LOG_DP for logs on datapath

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

On 3/3/2023 7:04 PM, Long Li wrote:
>> Subject: Re: [PATCH] net/mana: use RTE_LOG_DP for logs on datapath
>>
>> On 3/3/2023 2:16 AM, Long Li wrote:
>>>> Subject: Re: [PATCH] net/mana: use RTE_LOG_DP for logs on datapath
>>>>
>>>> On Thu, 23 Feb 2023 10:09:17 -0800
>>>> Stephen Hemminger <stephen@networkplumber.org> wrote:
>>>>
>>>>> On Thu, 23 Feb 2023 14:07:25 +0000
>>>>> Ferruh Yigit <ferruh.yigit@amd.com> wrote:
>>>>>
>>>>>> Overall I am not sure if anyone is interested in driver datapath
>>>>>> logs other than driver developers themselves.
>>>>>>
>>>>>> For datapath logging I think there are two concerns,
>>>>>> 1) It should not eat *any* cycles unless explicitly enabled
>>>>>> 2) Capability of enable/disable them because of massive amount of
>>>>>> log it can generate
>>>>>>
>>>>>>
>>>>>> Currently there are two existing approaches for driver datapath logging:
>>>>>> i)  Controlled by 'RTE_ETHDEV_DEBUG_RX/TX' compile time flag,
>>>>>>     when enabled 'rte_log()' is used with Rx/Tx specific log type.
>>>>>> ii) 'RTE_LOG_DP' ', compile time control per logtype via
>>>>>>     'RTE_LOG_DP_LEVEL',
>>>>>>      when enabled 'rte_log()' is used with PMD logtype.
>>>>>>
>>>>>>
>>>>>> In (ii), need to re-compile code when you need to increase the log
>>>>>> verbosity, and it leaks to production code as mentioned above.
>>>>>>
>>>>>> For (i), developer compiles once enabling debug, later can fine
>>>>>> grain log level dynamically. This is more DPDK developer focused
>> approach.
>>>>>>
>>>>>>
>>>>>> [1]
>>>>>> According above, what do you think to retire 'RTE_LOG_DP', (at
>>>>>> least within ethdev datapath), and chose (i) as preferred datapath
>> logging?
>>>>>
>>>>> I agree, the current tx/rx logging is a mess.
>>>>> Each driver is different, each driver has to have something to
>>>>> enable it; and it really isn't useful beyond the driver developer.
>>>>>
>>>>> Using tracing seems like a much better option. Could we agree on a
>>>>> common set of trace points for drivers and fix all drivers to use
>>>>> the same
>>>> thing.
>>>>> Probably will cause some upset among driver developers:
>>>>> "where did my nice printf's go, now I have to learn tracing"
>>>>> but DPDK has a good facility here, lets use it.
>>>>>
>>>>> My proposal would be:
>>>>> 	- agree on common set of trace points
>>>>> 	- apply to all drivers
>>>>> 	- remove RTE_LOG_DP()
>>>>> 	- remove per driver RX/TX options
>>>>> 	- side effect, more uses of RTE_LOGTYPE_PMD go away.
>>>>
>>>> Here is an example of using tracepoints instead.
>>>> Compile tested for example only.
>>>>
>>>> Note: using tracepoints it is possible to keep some of the
>>>> tracepoints even if fastpath is not enabled.  Things like running out
>>>> of Tx or Mbuf is not something that is perf critical; but would be good for
>> application to see.
>>>
>>> Thank you for the example.
>>>
>>> I sent another patch converting data path logs (mana) to trace points.
>>>
>>
>> Hi Long,
>>
>> Thanks for the effort, you were quick on this while discussion is going on.
>>
>> Although tracepoint is a good feature, I am not sure if it can fully replace the
>> logging.
>> I think usage is slightly different, trace is missing custom human readable
>> message, which can be very helpful for end user.
>>
>> And overall, it is a high level decision to switch logging to trace, it is
>> inconsistent to switch only single driver, perhaps techboard (cc'ed) can discuss
>> this.
>>
>> Until such consensus reached, I think driver should continue with logging.
>>
>>
>>
>> And for the logging, I suggest option (i) above, I was hoping more comments
>> but since it is missing I hope this can be discussed in techboard for a
>> conclusion.
> 
> Hi Ferruh,
> 
> Are you suggesting that MANA should use 'RTE_ETHDEV_DEBUG_RX/TX'?
> 
> I'm happy to implement the logging in this way.
> 

Yes, that looks to me better balance for compile time / runtime config
for drive developers.

But it prevents product code / end user to get data path logs, although
I believe this is OK I am not sure how useful datapath logs in
production code, that is why I am looking for more comment for a decision.

Let's wait for next techboard meeting, in case this is discussed there,
before making new implementation.