Re: [dpdk-dev] [PATCH 2/8] doc: add building with meson to linux GSG

["Burakov, Anatoly" <anatoly.burakov@intel.com>]

On 25-Nov-19 1:27 PM, Bruce Richardson wrote:
> On Mon, Nov 25, 2019 at 01:19:13PM +0000, Burakov, Anatoly wrote:
>> On 22-Nov-19 4:03 PM, Bruce Richardson wrote:
>>> Add instructions on building DPDK and using the pkg-config file to the
>>> linux GSG.
>>>
>>> Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
>>> ---
>>>    doc/guides/linux_gsg/build_dpdk.rst | 94 +++++++++++++++++++++++++++--
>>>    1 file changed, 90 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/doc/guides/linux_gsg/build_dpdk.rst b/doc/guides/linux_gsg/build_dpdk.rst
>>> index 7c0329fcc..5710effbc 100644
>>> --- a/doc/guides/linux_gsg/build_dpdk.rst
>>> +++ b/doc/guides/linux_gsg/build_dpdk.rst
>>> @@ -11,8 +11,8 @@ Compiling the DPDK Target from Source
>>>        Parts of this process can also be done using the setup script described in
>>>        the :ref:`linux_setup_script` section of this document.
>>> -Install the DPDK and Browse Sources
>>> ------------------------------------
>>> +Uncompress DPDK and Browse Sources
>>> +----------------------------------
>>>    First, uncompress the archive and move to the uncompressed DPDK source directory:
>>> @@ -33,8 +33,94 @@ The DPDK is composed of several directories:
>>>    *   config, buildtools, mk: Framework-related makefiles, scripts and configuration
>>> -Installation of DPDK Target Environments
>>> -----------------------------------------
>>> +Compiling and Installing DPDK System-wide
>>> +-----------------------------------------
>>> +
>>> +DPDK can be configured, built and installed on your system using the tools
>>> +``meson`` and ``ninja``.
>>> +
>>> +.. note::
>>> +
>>> +  The older makefile-based build system used in older DPDK releases is
>>> +  still present and it's use is described in section
>>
>> *its
>>
> Thanks.
> 
>>> +  `Installation of DPDK Target Environment using Make`_.
>>> +
>>> +DPDK Configuration
>>> +~~~~~~~~~~~~~~~~~~
>>> +
>>> +To configure a DPDK build use:
>>> +
>>> +.. code-block:: console
>>> +
>>> +     meson <options> build
>>> +
>>> +where "build" is the desired output build directory, and "<options>" can be
>>> +empty or one of a number of meson or DPDK-specific build options, described
>>> +later in this section. The configuration process will finish with a summary
>>> +of what DPDK libraries and drivers are to be built and installed, and for
>>> +each item disabled, a reason why that is the case. This information can be
>>> +used, for example, to identify any missing required packages for a driver.
>>> +
>>> +Once configured, to build and then install DPDK system-wide use:
>>> +
>>> +.. code-block:: console
>>> +
>>> +        cd build
>>> +        ninja
>>> +        ninja install
>>> +
>>> +Adjusting Build Options
>>> +~~~~~~~~~~~~~~~~~~~~~~~
>>> +
>>> +DPDK has a number of options that can be adjusted as part of the build configuration process.
>>> +These options can be listed by running ``meson configure`` inside a configured build folder.
>>> +Many of these options come from the "meson" tool itself and can be seen documented on the
>>> +`Meson Website <https://mesonbuild.com/Builtin-options.html>`_.
>>> +
>>> +For example, to change the build-type from the default, "debugoptimized",
>>> +to a regular "debug" build, you can either:
>>> +
>>> +* pass ``-Dbuildtype=debug`` or ``--buildtype=debug`` to meson when configuring the build folder initially
>>> +
>>> +* run ``meson configure -Dbuildtype=debug`` inside the build folder after the initial meson run.
>>> +
>>> +Other options are specific to the DPDK project but can be adjusted similarly.
>>> +To set the "max_lcores" value to 256, for example, you can either:
>>> +
>>> +* pass ``-Dmax_lcores=256`` to meson when configuring the build folder initially
>>> +
>>> +* run ``meson configure -Dmax_lcores=256`` inside the build folder after the initial meson run.
>>
>> This *very* welcome. It's a pity it's not possible to run these /before/
>> creating a build directory, but i'll take it!
>>
> 
> Can you clarify what you mean here? Passing max_lcores to the initial meson
> run isn't sufficient, you think?

No, i mean showing the available options. I don't think there's a way to 
show configuration options without creating a build directory first.

> 
>> A common source of confusion for people building example apps with meson is
>> that, unlike with make, you don't build DPDK first and then build examples,
>> you build them all at once. Perhaps it would be worth calling this out
>> explicitly?
>>
> I was actually thinking that that functionality was primarily targeted at
> developers rather than at end users. However, I can include the -Dexamples
> flag for reference here for people.

I'm speaking of "developer used to building DPDK with make" target 
audience. It has been my experience (of pushing people to use meson) 
that this is a major point of confusion when it comes to using meson for 
DPDK development.

> 
>> Also, kinda unrelated to this, but can we add an "all" target that actually
>> fails if one of the examples doesn't build? IIRC currently it'll just skip
>> through any that don't build, which is not ideal for quick compile testing.
>> I mean, obviously apps that don't have their dependencies met shouldn't be
>> attempted, but if any /buildable/ examples fail to build, i think there
>> should be a way to communicate this without having to explicitly call out
>> all example apps in the -Dexamples option. (if it currently works that way,
>> disregard!)
> 
> This should indeed be the way it currently works. The examples to be built
> depends upon the detected dependencies at configure time, but thereafter on
> compile, ninja knows nothing about examples or otherwise, it just sees code
> to be compiled and linked and should error out if anything fails. If this
> is not the case, it's a bug we need to fix.

Then disregard :)

> 
>>
>>> +
>>> +Building Applications Using Installed DPDK
>>> +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>> +
>>> +When installed system-wide, DPDK provides a pkg-config file ``libdpdk.pc`` for applications to query as part of their build.
>>> +It's recommended that the pkg-config file be used, rather than hard-coding the parameters (cflags/ldflags)
>>> +for DPDK into the application build process.
>>> +
>>> +An example of how to query and use the pkg-config file can be found in the ``Makefile`` of each of the example applications included with DPDK.
>>> +A simplified example snippet is shown below, where the target binary name has been stored in the variable ``$(APP)``
>>> +and the sources for that build are stored in ``$(SRCS-y)``.
>>> +
>>> +.. code-block:: makefile
>>> +
>>> +        PKGCONF = pkg-config
>>> +
>>> +        CFLAGS += -O3 $(shell $(PKGCONF) --cflags libdpdk)
>>> +        LDFLAGS += $(shell $(PKGCONF) --libs libdpdk)
>>> +
>>> +        $(APP): $(SRCS-y) Makefile
>>> +                $(CC) $(CFLAGS) $(SRCS-y) -o $@ $(LDFLAGS)
>>
>> What about a meson-based example?
>>
> I didn't think such a thing would be work including, since the number of
> end-user apps using meson is likely fairly small. We'd also then need to
> include an example using cmake or other build systems too, for
> completeness.

That's a bit of a false equivalence though, because DPDK doesn't support 
CMake, while it does support meson - so it makes sense to provide 
instructions for meson as well. If you only provide instructions for 
make, people will end up using make just because it's less effort to 
"use what you know" than switching to build DPDK using meson *and* 
figuring out how to use meson for your app development as well.

For example, whenever i need to build a quick-n-dirty DPDK app outside 
of DPDK tree, i use meson because it's the thing i now know that is 
better than make (syntax-wise at least), but it took me a while to 
figure out how to build a DPDK app using meson outside of DPDK build 
tree. The process would've been much easier if there was a ready-made 
example of how to do that.

-- 
Thanks,
Anatoly