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

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

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.