A brief twitter observation convinced me to dig into our build system
effeciency. First off, some numbers from a -j10 build after a `make clean`:
origin/master:
real 3m51.867s
user 3m41.425s
sys 0m10.434s
jdm/parbuild [1]:
real 2m36.697s
user 4m9.334s
sys 0m10.177s
With the changes from my parbuild branch, we build all subdirectories in
parallel, then libmsg and libutil together, libnet by itself, then
libgfx and libscript build together, followed by the main servo crate.
It's probably possible to decouple libgfx from libnet (there are
precisely two references to the Image type from libnet), but that
wouldn't actually affect the total build time in a parallel setting,
since libgfx takes 12 seconds, libscript takes 60s, the servo crate
takes 46s, and the rest are on the low end of less than 10 seconds.
libscript is obviously the long tail, and it's going to get worse as
time goes on.
With all that said, the main change of moving Au from libgfx to libutil
to decouple libscript from libgfx is not thrilling, but possibly worth
it. At this point, the biggest clean build wins will come from real
submodule dependencies, and incremental build wins from splitting up
libscript somehow into isolated crates. Not really sure how to do that,
unfortunately.
The other big win comes from removing our incorrect use of the
..NOPARALLEL target from our makefiles. Whether this would bring back our
old problems of phantom dependency problems for which it was originally
added is unclear, but it looks to me like the other changes in that
commit [2] should make it unnecessary.
I guess I'll make a PR for my changes so we can debate about the win of
building libgfx and libscript in parallel versus the hold-your-nose
feeling of moving Au into libutil.
Cheers,
Josh
[1]
https://github.com/jdm/servo/commit/cecc02d918a546eee4b7e17fe8bad00c2cafe968
[2]
https://github.com/mozilla/servo/commit/3a5d9bdae27a9bcb43e43cb6603b5e5bc29bbe82
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