[RFC libdrm 0/2] Replace the build system with meson

[Dylan Baker]

Quoting Ilia Mirkin (2017-03-16 14:32:09)
> On Thu, Mar 16, 2017 at 5:25 PM, Dylan Baker <dylan at pnwbakers.com> wrote:
> > Why bother, and why would we want this?                                                              │~
> >
> > First it's written in python, which means the potential developer base
> > is massive. And it provides a recursive view for humans, but a
> > non-recursive view for the system. This is the best of both worlds,
> > humans can organize the build system in a way that makes sense, and the
> > machine gets a non-recursive build system. It also uses ninja rather
> > than make, and ninja is faster than make inherently. Meson is also a
> > simpler syntax than autotools or cmake it's not Turing Complete by
> > design nor does it expose python, again, by design. This allows meson
> > itself to be reimplemented in a another language if python becomes a
> > dead-end or a bottle-neck. It also makes it much easier to understand
> > what the build system is doing.
> >
> > What's different about using meson?
> >
> > Well, apart from a faster builds and less magic in the build system? The
> > configure flags are different, it uses -D<opt>=<value> more like cmake
> > than the --enable or --with flags of autotools, although oddly it uses
> > --prefix and friends when calling meson, but not with mesonconf, there's
> > a bug opened on this. Meson also doesn't support in-tree builds at all;
> > all builds are done out of tree. It also doesn't provide a "make dist"
> > target, fortunately there's this awesome tool called git, and it
> > provides a "git archive" command that does much the same thing. Did I
> > mention it's fast?
> >
> > Here are the performance numbers I see on a 2 core 4 thread SKL, without
> > initial configuration, and building out of tree (using zsh):
> >
> > For meson the command line is:
> > time (meson build -Dmanpages=true && ninja -C build)
> >
> > For autotools the command line is:
> > time (mdkir build && cd build && ../autotools && make -j5 -l4)<Paste>
> 
> Probably mkdir...

derp, yeah.

> 
> >
> > meson (cold ccache):     13.37s user 1.74s system 255% cpu  5.907 total
> > autotools (cold ccache): 26.50s user 1.71s system 129% cpu 21.835 total
> > meson (hot ccache):       2.13s user 0.39s system 154% cpu  1.633 total
> > autotools (hot ccache):  13.93s user 0.73s system 102% cpu 14.259 total
> >
> > That's ~4x faster for a cold build and ~10x faster for a hot build.
> >
> > For a make clean && make style build with a hot cache:
> > meson:     4.64s user 0.33s system 334% cpu 1.486 total
> > autotools: 7.93s user 0.32s system 167% cpu 4.920 total
> >
> > Why bother with libdrm?
> >
> > It's a simple build system, that could be completely (or mostly
> > completely) be ported in a very short time, and could serve as a tech
> > demo for the advantages of using meson to garner feedback for embarking
> > on a larger project, like mesa (which is what I'm planning to work on
> > next).
> >
> > tl;dr
> >
> > I wrote this as practice for porting Mesa, and figured I might as well
> > send it out since I wrote it.
> >
> > It is very likely that neither of these large patches will show up on the
> > mailing list, but this is available at my github:
> > https://github.com/dcbaker/libdrm wip/meson
> 
> I haven't looked at meson or your patches in detail, but autotools
> supports 2 very important use-cases very well:
> 
> 1. ./configure --help
> 2. Cross-compilation with minimal requirement from the project being built
> 
> Can you comment on how these are handled in meson?
> 
> Cheers,
> 
>   -ilia

1. mesonconf <builddir> provides much the same thing. You can also read the
meson_options.txt file, which is generally pretty short. I haven't added
descriptions to the options in this patch.

2. you write a small ini style configuration file, something like:
[binaries]
c = '/usr/bin/aarch64-linux-gnu-gc'
ar = '/usr/bin/aarch64-linux-gnu-gcc-ar'
strip = '/usr/bin/aarch64-linux-gnu-strip'
pkg-config = '/usr/bin/aarch64-linux-gnu-pkgconfig'

Then you just configure with:
meson build --cross-file cross_file.txt

then just ninja like normal

There's a more detailed walkthrough here:
https://github.com/mesonbuild/meson/wiki/Cross-compilation

I was able to cross compile the arm libraries for aarch64 using basically the
above configuration (I had to write a wrapper script for pkg-config to set a
couple of environment variables and install and archlinux aarach64 chroot,
because arch), of course, I don't have access to any arm machines that I could
test with.

Dylan
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