sched/fair: A bit of a cgroup/PELT overhaul

Hi all,

New this time is that Josef identified and fixed a problem he had with it. He
also provided many compile fixes. Meanwhile I managed to reflow the patches so
that the whole now looks like a normal patch series.

Other than that, it should still very much be what it was before.. From the
previous announce:

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So after staring at all that PELT stuff and working my way through it again:

  https://lkml.kernel.org/r/20170505154117.6zldxuki2fgyo53n...

I started doing some patches to fix some of the identified broken.

So here are a few too many patches that do:

 - fix 'reweight_entity' to instantly propagate the change in se->load.weight.

 - rewrite/fix the propagate on migrate (attach/detach)

 - introduce the hierarchical runnable_load_avg, as proposed by Tejun.

 - synchronous detach for runnable migrates

 - aligns the PELT windows between a cfs_rq and all its se's

 - deals with random fallout from the above (some of this needs folding back
   and reordering, but its all well past the point I should post this anyway).


IIRC pjt recently mentioned the reweight_entity thing, and I have very vague
memories he once talked about the window alignment thing -- which I only
remembered after (very painfully) having discovered I really needed that.

In any case, the reason I did the reweight_entity thing first, is because I
feel that is the right place to also propagate the hierarchical runnable_load,
as that is the natural place where a group's cfs_rq is coupled to its
sched_entity.

And the hierachical runnable_load needs that coupling. TJ did it by hijacking
the attach/detach migrate code, which I didn't much like.  In any case, all
that got me looking at said attach/detach migrate code and find pain. So I went
and fixed that too.

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Still very many thanks to Vincent, Dietmar and Josef for poking at these patches.

If nothing untowards happens, I plan to get them merged after the immenent
merge window.