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

[Long Li <longli@microsoft.com>]

> -----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?

Thanks,
Long