[RFE] binpack available jobs by historical timings

[mathstuf]

If Ninja could schedule available jobs using previous timings, faster compilation might be possible. See http://www.cmake.org/Bug/view.php?id=14898#c35793.

[nico]

That's true if you have jobs that are mostly independent and that have very different run lengths. I think that part is mostly a dupe of #232 maybe (which has some more discussion, and links to another issue with yet more discussion.)

(For cmake, I'm told that part of the reason this comes up so often (but not for this bug) is that cmake used to generate overconstrained dependencies. I'm told this is better in 2.8.12+.)

[nico]

(Mostly note to self: Bugs on cmake dependencies: http://www.cmake.org/Bug/view.php?id=13799 http://www.cmake.org/Bug/view.php?id=14726#c35023)

[mathstuf]

Ah, yeah, #232 looks very similar. I'm actually fixing the CMake dependency constraints now :) . Basically, if liba depends on libb, all of liba's sources depend on libb's link step (this is to ensure that any custom commands which libb depends on which may be implicit at liba are satisfied). The solution is to break the sources' dependency on libb if libb's custom_command dependencies are a subset of liba's custom_command dependencies.