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

[Bruce Richardson <bruce.richardson@intel.com>]

On Mon, Apr 20, 2020 at 06:11:30PM +0100, Bruce Richardson wrote:
> On Mon, Apr 20, 2020 at 04:43:21PM +0200, Lukasz Wojciechowski wrote:
> > 
> > W dniu 20.04.2020 o 16:21, Bruce Richardson pisze:
> > > On Mon, Apr 20, 2020 at 01:37:12PM +0000, Ananyev, Konstantin wrote:
> > >>>
> <snip>
> > >> 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.
> 
> /Bruce

Apologies for the self-reply, but I'd also like to ensure that basing it
all off the meson debug flag is the right thing to do. Currently that flag
is used to place debug info in the binary, which is quite different to
turning all a massive amount of prints from each component. Some drivers
etc. can be very chatty when debug flags are on.

A further option might be to have a general debug_drivers or
debug_libraries option, working with globs in the same was as the current
"disable_drivers" option does. That would allow more fine grain debugging
without resorting to manual CFLAG hacking, and it would also keep separate
the debug info from the compiler (which adds no perf hit) from debug prints
from drivers and libs which definitely do.

/Bruce