[$] The trouble with iowait

CPU scheduling is a challenging job; since it inherently requires makingguesses about what the demands on the system will be in the future, itremains reliant on heuristics, despite ongoing efforts to remove them.Some of those heuristics take special note of tasks that are (or appear tobe) waiting for fast I/O operations. There is some unhappiness, though,with how this factor is used, leading to a couple of patches taking ratherdifferent approaches to improve the situation.