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

[Neil Armstrong]

On 03/16/2017 10:57 PM, Dylan Baker wrote:
> 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'

I'm sure meson is a good tool, but a simple :
./configure --target=arch64-linux-gnu

is wayyyy simpler...

And the only requirement is "sh" for autotools.

Neil

> 
> 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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