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

Luca Boccassi bluca at debian.org
Thu May 30 13:06:55 CEST 2019


On Thu, 2019-05-30 at 13:03 +0300, Ilya Maximets wrote:
> On 29.05.2019 23:37, 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.
> 
> So how can I do this? I don't think 'ninja install' has such option.
> Also, if you think that it is safe to skip some libs/drivers in
> installation
> process, it must be safe to not build them at all. It's just a waste
> of
> time and computational resources to build something known to be not
> used.
> And if you're going to ship DPDK libraries separately in distros,
> you'll
> have to test their different combinations anyway. If they're so
> independent
> that you don't need to test them in various combinations, than your
> point
> about test matrix is not valid.

It can be done in the packaging step, or post-install if there's no
packaging. An operating system vendor is free to do its own test and
support plan, and decide to leave out some PMDs from it. Canonical does
something similar: in Debian/Ubuntu and derivatives we package PMDs
individually, and then Canonical groups them in 2 sets - a subset they
guarantee to support from their own resources, and the full set as
delivered by the community. But the point is that it's a step that they
decide to take, and pay the price for it in terms of time investment in
validating that particular combination, rather than the onus being on
our very limited and already stretched resources to validate all
combinations.

We can focus our resources into making sure the few combinations that
_must_ be supported, for example due to external dependencies, work
fine.

> > Sorry, but from me it's a very strong NACK.
> 
> Sorry, but let me disagree with you. For me, meson configurability is
> the
> essential thing to have in terms of deprecating the 'make' build
> system.
> DPDK was and keeps being (in most cases) the library that users
> statically
> linking to a single application built for particular platform and not
> using
> for anything else. This means that user in most cases knows which
> parts
> needed and which parts will never be used. Current meson build system
> doesn't allow to disable anything forcing users to link with the
> whole bunch
> of unused code.
> 
> One major case is that you have to have build environment equal to
> your
> target platform in terms of availability of external libraries. So,
> if I
> have some external library on build system, meson will build all the
> modules
> it depends from and will link them to my application. As a result
> I'll not
> be able to run my application on a target platform without installing
> additional dependencies which is not acceptable. This patch will
> allow to
> specifically disable all the libs that has unsatisfiable dependencies
> on
> target. Without the patch it's required to manually remove resulted
> libs and
> fix pkg-config and stuff before building apps. This is far less user-
> friendly
> than options I proposed. And yes, I still have to waste time for
> building
> libraries I'll remove right after.
> 
> While testing OVS on TravisCI, DPDK was built far more than 30K times
> which is more than half of a year of a wasted computational resources
> (if we'll count 10 minutes per build).
> I think this time could be used more wisely.
> 
> Best regards, Ilya Maximets.

But that's the thing: as it was discussed recently, we need to move
away from DPDK being by default a "special sauce" toolkit with millions
of customizations that is custom built and statically linked, like
busybox, and to a situation where it's just another set of system
libraries like any other, shipped by the operating system, like glibc -
see the threads about stable API/ABI and OS-driven delivery by Ray.
The status quo of an insanely granular build configuration that means
everyone is using something different from each other is a bug - not a
feature. Excessive _build time_ configuration exacerbates and
encourages this bug.

Sure, an initial build from scratch will take a couple of minutes more
- mildly annoying, but worth the price. Caching takes care of that
problem already pretty well. Also standardizing on radically fewer
build configurations means you _don't_ have to rebuild DPDK for third
party testing - you just consume the pre-built binaries from the OS of
choice, or the PPA or similar for backports and HEAD builds. That will
save even more time and resources in third-party build systems.

-- 
Kind regards,
Luca Boccassi


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