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 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.

Long