Reconsidering the scheduler's wake_wide() heuristic

This patch does not look inspired by MPI codes. But there are some odd phrases in the article's introduction that probably triggered the original post's worries. Many large-scale parallel codes very much work in lock step in critical areas. Consider the all-to-all reduction for computing a residual (error term stand-in) and determining convergence. That is the opposite of the article's statement that parallel programs respond randomly...

I also have plenty of confusing data on packing v. spreading for irregular data analysis (e.g. graph algorithms). The cache locality already is kinda meh, and you often get better performance from engaging more memory controllers simultaneously and having the larger aggregate L3 across all CPUs. But not always, and there is no clear indicator that I can see from my codes. I also haven't had the time / student to dig into the choices. No heuristic will be right for everyone.