xserver autotools questions

[Jamey Sharp]

Hi Dan!

On Mon, May 24, 2010 at 12:01 PM, Dan Nicholson <dbn.lists at gmail.com> wrote:
> On Sun, May 23, 2010 at 10:34 AM, Jamey Sharp <jamey at minilop.net> wrote:
>> First, it's been bugging me that a full build of the X server takes so
>> long, since I keep changing header files that are used everywhere. I
>> believe switching to non-recursive automake and killing the
>> intermediate libraries for each subdirectory would help a lot, but
>> when I tried to test that hypothesis, the mass of configure.ac
>> declarations defeated me. Can any autotools experts help me out here?
>
> I don't see what non-recursive has to do with it. Automake has
> automatic dependency generation that will cause source files to be
> recompiled if headers are updated. Non-recursive directories doesn't
> change that one bit.

Yes, dependency generation is great, and I wouldn't want to lose it. I
should have started with the symptoms I was hoping to fix: I can't
currently saturate the two cores in my laptop, let alone the four in
the box next to me. I don't think I'm I/O bound, since the whole
source tree is usually in cache from a build moments earlier. It seems
like there just isn't enough work available at once.

I'm building with make -j (doesn't matter whether I use -j6 or just
-j), ccache, and distcc, and as I see it, the trouble is that there's
no parallelism across directories.

There's no way to fix that with recursive make, is there?

> The convenience libraries for each subdirectory also don't affect
> things.

Time spent in the linker hurts, but if it were parallelized with the
rest of the build, I suppose it would hurt a lot less. Still, as I
understand it there's no reason to use the convenience libraries in a
non-recursive build, and *handwave* it seems like running the linker
less often should be better.

> There are reasons to do non-recursive make. However, I don't think
> this is one of them.

If I had a good reason to do non-recursive make in the xserver, how
would you go about getting started? :-)

>> Second, I want to factor out code that's shared between two or more
>> DDXes into a common place. My first target is merging
>> dmxComputeScreenOrigins with xf86InitOrigins, because I had to make
>> almost-identical edits to both for a MAXSCREENS removal patch I just
>> built. Where should that go, and how do I get autotools to link it
>> correctly?
>
> Making a convenience library out of the common source files with
> noinst_LTLIBRARIES? Of course, that appears to be the part you're
> trying to avoid above. But the linking is that you just add it to
> _SOURCES for whatever _PROGRAMS or _LTLIBRARIES it needs to be in.

It looked like the xserver tree has a much more complicated plan
going, involving listing every convenience library in variables
substituted from configure.ac, or something? I'd have copied some
existing bits if I could figure out what the plan was.

I was also trying to ask a more stylistic question, of where this
particular code ought to live in the tree.

Jamey