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

[Ilia Mirkin]

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...

>
> 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