sched/fair: Rework and comment the group_imb code
sched/fair: Rework and comment the group_imb code

Rik reported some weirdness due to the group_imb code. As a start to
looking at it, clean it up a little and add a few explanatory
comments.

Signed-off-by: Peter Zijlstra <3fddac958924aef220f202ca567388ddab3f14a8@infradead.org>
Link: c64706aa9447b0e68d03a9aaa7040266dab44211@git.kernel.org
Signed-off-by: Ingo Molnar <9dbbbf0688fedc85ad4da37637f1a64b8c718ee2@kernel.org>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs