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

[Long Li <longli@microsoft.com>]

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

Thank you.

I have submitted several other patches since this patch was submitted. There may be some conflicts.

Please let me know if I should rebase this patch to latest code so it will be straightforward to apply.

Long