Re: [dpdk-dev] [PATCH v1 03/17] ethdev: replace library debug flag with global one

["Ananyev, Konstantin" <konstantin.ananyev@intel.com>]

> > > > > > >> I am agree with Cristian concern here: that patch removes ability to
> > > > > > >> enable/disable debug on particular library/PMD.  If the purpose is to
> > > > > > >> minimize number of config compile options, I wonder can't it be done
> > > > > > >> in a slightly different way: 1. introduce gloabal RTE_DEBUG 2. keep
> > > > > > >> actual .[c,h] files intact 3. In actual librte_xxx/meson.build  file
> > > > > > >> check if RTE_DEBUG is enabled, If yes, then enable particular debug
> > > > > > >> flag for these libs.  Something like: If dpdk_conf.get('RTE_DEBUG') ==
> > > > > > >> true dpdk_conf.set('RTE_LIBRTE_XXX_DEBUG ', 1)
> > > > > > >>
> > > > > > >> defines that are used by multiple libs, probably can be set in upper
> > > > > > >> layer meson.build.
> > > > > > >>
> > > > > > >> That way will have global 'debug' flag, but users will still have an
> > > > > > >> ability to enable/disable debug flags on a per lib basis via
> > > > > > >> CFLAGS="-D..."
> > > > > > >>
> > > > > > >> Konstantin
> > > > > > >>
> > > > > > > That seems a reasonable idea to me.
> > > > > > >
> > > > > > > However, in this case, we don't need the RTE_DEBUG flag at all, we can
> > > > > > > either:
> > > > > > >
> > > > > > > * allow each component meson.build file define its own flags after
> > > > > > > checking get_option('debug') * have lib/meson.build and
> > > > > > > drivers/meson.build automatically define a specific define for each
> > > > > > > library or driver to standardize the naming.  [This would save anyone
> > > > > > > working on it from having to lookup what the define was, since it's
> > > > > > > always e.g. RTE_DEBUG_ + library-base-name, e.g.  RTE_DEBUG_LPM,
> > > > > > > RTE_DEBUG_SCHED etc]
> > > > > > >
> > > > > > > Theoretically we can also do both, have the standard ones defined and
> > > > > > > then allow a component to provide extra flags itself if so desired.
> > > > > > >
> > > > > > > /Bruce
> > > > > > OK, so let's summarize how the patches should be redo: * usage of global
> > > > > > "debug" flag for meson build stays * we standardize names of debug flags
> > > > > > in the components to RTE_DEBUG_ + components name * debug flag enables al
> > > > > > the RTE_DEBUG_... flags
> > > > > >
> > > > > > This allow to easily use both: * the debug flag - to enable all debugs *
> > > > > > or define manually RTE_DEBUG+component name, just for debug from a single
> > > > > > component
> > > > > >
> > > > > > I like Bruce's idea of adding it to the lib/meson.build and
> > > > > > drivers/meson.build. This way they will be added to dpdk_conf meson
> > > > > > object and written then later to rte_build_config.h before compilation
> > > > > > stage.  All the other modules will be able to use these flags.
> > > > > >
> > > > > Sounds good to me (obviously!), but I'd like other feedback to ensure
> > > > > others are ok with this before you spend too much effort implementing it.
> > > > >
> > > > > For the drivers, the flag probably needs to include the category as well as
> > > > > the name, e.g. RTE_DEBUG_NET_IXGBE, RTE_DEBUG_RAW_IOAT, to avoid possible
> > > > > name confusion. Those flags can then be checked inside individual
> > > > > meson.build files to enable other debug flags if necessary e.g. in ixgbe,
> > > > > you could theoretically do:
> > > > >
> > > > > if dpdk_conf.has('RTE_DEBUG_NET_IXGBE')
> > > > > 	cflags += '-DRTE_LIBRTE_IXGBE_DEBUG_RX'
> > > > > 	cflags += '-DRTE_LIBRTE_IXGBE_DEBUG_TX'
> > > > > 	...
> > > > > endif
> > > > >
> > > > > to enable more fine-grained control if so desired, and to maintain
> > > > > compatibility with existing defines, again if so desired.
> > > >
> > > > Nak the nak from Cristian.
> > > >
> > > > We don't need all these flags.
> > > > If the user choose to compile DPDK for debug, every debug facilities
> > > > should be enabled. Then at runtime it is possible to enable/disable
> > > > the interesting logs.
> > > > If you need to disable something which is not a log,
> > > > you can align with the log level thanks to the function rte_log_can_log.

For many libs these flags mean much more than just logging.
Let say RTE_LIBRTE_ETHDEV_DEBUG changes behaviour of tx_prepare() for many
drivers - extra validation performed.
RTE_LIBRTE_MBUF_DEBUG makes __rte_mbuf_sanity_check() a call  to real
rte_mbuf_sanity_check() instead of just NOP.
Which means performance would be greatly affected.
RTE_LIBRTE_MEMPOOL_DEBUG changes format of the mempool object header
and enforce extra checking, stats collection.
etc.
Probably that's ok for some cases to enable all that extra validation we have at once.
But I suppose in many cases people just interested to enable debug on one
(ok might be two/three) particular libraries, not the whole system.
Right now there is such ability, we are going to remove it without
providing adequate replacement.   
Approach with rte_log_can_log() seems workable,
but right now these patches don't implement it. 
Konstantin

> > > >
> > > > Please let's stop complicating things for the contributors and the users.
> > > > Note: I am strong on this position.
> > > >
> > > Note, this means that you need to ensure all debug printouts from libs and
> > > drivers are using the RTE_LOG macros so can be runtime controlled. I think
> > > that may be some distance from reality right now.
> >
> > Perfect! Let's expose those nasty logs which are not (yet) controllable.
> > And next step is to block any patch in those drivers or libs,
> > until it is fixed. Dynamic logging should have been complete for long.
> >
> I can live with that, I suppose. Do we have any idea of the magnitude of
> the work required here?
> 
> > > Even if we do want all debug enabled from one flag, I'm still not 100%
> > > convinced that the existing debug flag is the way to do, since it only adds
> > > debug info to binary without affecting code generation.
> >
> > OK, we want to keep this flag for gdb symbols only?
> > And add a new flag for debugging facilities which hurt the runtime performance?
> >
> I think that would be wise, yes. We can call the option "rte_debug" or
> something instead.
> 
> /Bruce