Re: [RFC PATCH] replace DPDK config and build system

[Stephen Hemminger <stephen@networkplumber.org>]

On Thu, 8 Jun 2017 09:59:01 +0100
Bruce Richardson <bruce.richardson@intel.com> wrote:

> On Wed, Jun 07, 2017 at 04:26:17PM -0700, Stephen Hemminger wrote:
> > On Wed,  7 Jun 2017 11:47:42 +0100
> > Bruce Richardson <bruce.richardson@intel.com> wrote:
> >   
> > > The prototype is incomplete, but it does build a reasonable number of our
> > > libraries, some unit tests, the i40e PMD and the testpmd binary, and I have
> > > successfully passed traffic using testpmd from the build. Some things are
> > > not fully correct, e.g. static builds aren't working right now, as I haven't
> > > correctly done all the dependency tracking, I think, and the cpu flag
> > > detection has issues. It also has only been tried on x86_64 linux, on a
> > > couple of systems, so YMMV. However, I feel it's a reasonable enough start
> > > point to show what we might be able to achieve.  
> > 
> > Remember that in many cases the build system and the target system are different.
> > One of the problems with previous DPDK builds where build system was on bare metal
> > but deployment target was on a more limited VM environment. I sweated through
> > lots of  pain on that.  
> 
> Yep, and I'm not going to claim that this is going to solve world hunger
> here :-) or that switching is going to be easy. However, talking of
> building and deploying on different targets, meson is designed to allow
> cross-compilation, see for example the built-in objects for
> "build_machine", "host_machine" and "target_machine":
> http://mesonbuild.com/Reference-manual.html#build_machine-object
> 
> Also, one thing I did add into this prototype was some build argument
> support to test how that would work. By default, when you run meson, it
> will set up the cflags to pass in -march=native, much as is done by our
> default targets now. However, this is easily changed when doing your own
> builds, for example, to do two different builds in different directories:
> 
> $ meson native_build
> ...
> Checking for value of define "__PCLMUL__": 1
> Checking for value of define "__AVX__": 1
> Checking for value of define "__AVX2__": 1
> ...
> 
> $ meson -Dmachine=ivybridge ivybridge_build
> ...
> Checking for value of define "__PCLMUL__": 1
> Checking for value of define "__AVX__": 1
> Checking for value of define "__AVX2__":
> ...
> 
> This way you can easily set up different builds for different machine
> targets, with different instruction set levels, as seen from where the
> second case above did not report AVX2 support. The project-specific
> options are given in meson_options.txt. See also relevant section in
> meson docs: http://mesonbuild.com/Build-options.html
> 
> Regards,
> /Bruce

On a side note, it would be good to use the GCC extensions that allow
building different versions of the same routine into one binary.