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

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

On 4/28/2023 2:29 AM, Long Li wrote:
> 
> 
>> -----Original Message-----
>> From: Ferruh Yigit <ferruh.yigit@amd.com>
>> Sent: Friday, March 3, 2023 5:15 PM
>> To: Long Li <longli@microsoft.com>; Stephen Hemminger
>> <stephen@networkplumber.org>
>> Cc: longli@linuxonhyperv.com; Thomas Monjalon <thomas@monjalon.net>;
>> Andrew Rybchenko <andrew.rybchenko@oktetlabs.ru>; Jerin Jacob
>> Kollanukkaran <jerinj@marvell.com>; David Marchand
>> <david.marchand@redhat.com>; dev@dpdk.org; Ajay Sharma
>> <sharmaajay@microsoft.com>; stable@dpdk.org; Luca Boccassi
>> <bluca@debian.org>; Qi Z Zhang <qi.z.zhang@intel.com>; Ajit Khaparde
>> <ajit.khaparde@broadcom.com>; Bruce Richardson
>> <bruce.richardson@intel.com>; Konstantin Ananyev
>> <konstantin.v.ananyev@yandex.ru>; Olivier Matz <olivier.matz@6wind.com>;
>> Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>; techboard@dpdk.org
>> Subject: Re: [PATCH] net/mana: use RTE_LOG_DP for logs on datapath
>>
>> 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.
> 
> HI Ferruh,
> 
> Have we reached a decision on how to implement data path logs?
> 

Hi Long,

I am not aware of a result on the matter, let me continue with this
patch to not block it more.