Re: [dpdk-dev] [PATCH 2/2] meson: make build configurable

[Ilya Maximets <i.maximets@samsung.com>]

On 30.05.2019 13:22, Bruce Richardson wrote:
> On Wed, May 29, 2019 at 09:37:20PM +0100, Luca Boccassi wrote:
>> On Wed, 2019-05-29 at 19:39 +0300, Ilya Maximets wrote:
>>> The first thing many developers do before start building DPDK is
>>> disabling all the not needed divers and libraries. This happens
>>> just because more than a half of DPDK dirvers and libraries are not
>>> needed for the particular reason. For example, you don't need
>>> dpaa*, octeon*, various croypto devices, eventdev, etc. if you're
>>> only want to build OVS for x86_64 with static linking.
>>>
>>> By disabling everything you don't need, build speeds up literally 10x
>>> times. This is important for CI systems. For example, TravisCI wastes
>>> 10 minutes for the default DPDK build just to check linking with OVS.
>>>
>>> Another thing is the binary size. Number of DPDK libraries and,
>>> as a result, size of resulted statically linked application decreases
>>> significantly.
>>>
>>> Important thing also that you're able to not install some
>>> dependencies
>>> if you don't have them on a target platform. Just disable
>>> libs/drivers
>>> that depends on it. Similar thing for the glibc version mismatch
>>> between build and target platforms.
>>>
>>> Also, I have to note that less code means less probability of
>>> failures and less number of attack vectors.
>>>
>>> This patch gives 'meson' the power of configurability that we
>>> have with 'make'. Using new options it's possible to enable just
>>> what you need and nothing more.
>>>
>>> For example, following cmdline could be used to build almost minimal
>>> set of DPDK libs and drivers to check OVS build:
>>>
>>>   $ meson build -Dexamples='' -Dtests=false -Denable_kmods=false \
>>>                 -Ddrivers_bus=pci,vdev          \
>>>                 -Ddrivers_mempool=ring          \
>>>                 -Ddrivers_net=null,virtio,ring  \
>>>                 -Ddrivers_crypto=virtio         \
>>>                 -Ddrivers_compress=none         \
>>>                 -Ddrivers_event=none            \
>>>                 -Ddrivers_baseband=none         \
>>>                 -Ddrivers_raw=none              \
>>>                 -Ddrivers_common=none           \
>>>                
>>> -Dlibs=kvargs,eal,cmdline,ring,mempool,mbuf,net,meter,\
>>>                        ethdev,pci,hash,cryptodev,pdump,vhost \
>>>                 -Dapps=none
>>>
>>> Adding a few real net drivers will give configuration that can be
>>> used
>>> in production environment.
>>>
>>> Looks not very pretty, but this could be moved to a script.
>>>
>>> Build details:
>>>
>>>   Build targets in project: 57
>>>
>>>   $ time ninja
>>>   real    0m11,528s
>>>   user    1m4,137s
>>>   sys     0m4,935s
>>>
>>>   $ du -sh ../dpdk_meson_install/
>>>   3,5M    ../dpdk_meson_install/
>>>
>>> To compare with what we have without these options:
>>>
>>>   $ meson build -Dexamples='' -Dtests=false -Denable_kmods=false
>>>   Build targets in project: 434
>>>
>>>   $ time ninja
>>>   real    1m38,963s
>>>   user    10m18,624s
>>>   sys     0m45,478s
>>>
>>>   $ du -sh ../dpdk_meson_install/
>>>   27M     ../dpdk_meson_install/
>>>
>>> 10x speed up for the user time.
>>> 7.7 times size decrease.
>>>
>>> This is probably not much user-friendly because it's not a Kconfig
>>> and dependency tracking in meson is really poor, so it requires
>>> usually few iterations to pick correct set of libraries to satisfy
>>> all dependencies. However, it's not a big deal. Options intended
>>> for a proficient users who knows what they need.
>>
>> Hi,
>>
>> We talked about this a few times in the past, and it was actually one
>> of the design goals to _avoid_ replicating the octopus-like config
>> system of the makefiles. That's because it makes the test matrix
>> insanely complicated, not to mention the harm to user friendliness,
>> among other things.
>>
>> If someone doesn't want to use a PMD, they can just avoid installing it
>> - it's simple enough.
>>
>> Sorry, but from me it's a very strong NACK.
>>
> I would agree with this position - tracking the dependencies of the
> libraries etc. is a nightmare, and requires lots of ifdef'ery in the code
> for handling cases where libraries don't exist.
> 
> However, I might be ok with limiting the drivers somewhat, since they don't
> tend to depend on each other so much, though ideally I'd still prefer to
> have one build of DPDK that has minimal configuration. If we say that we
> can disable some drivers, though,  issue then becomes whether e.g. the bus
> drivers could selectively be disabled, and the knock-on effects of that.
> I'd hate to see the case where we end up having the meson.build files for
> drivers becoming a massive list of conditional checks for a bunch of
> internal dependencies. If someone is wanting to do a custom build of DPDK,
> they can always patch out the subdirectories they don't want in the
> meson.build files - but because of testing matrixes for such
> configurations, I don't think its something we want to explicitly support.

Thanks Bruce.
I see your point.

Please, take a look at the first patch of this series. It doesn't directly
connected to this one, but should speed up meson configuration a bit.

Best regards, Ilya Maximets.