block, bfq: boost the throughput with random I/O on NCQ-capable HDDs

	 * The next variable takes into account the cases where idling

	 * boosts the throughput.

	 *

	 * The value of the variable is computed considering that

	 * idling is usually beneficial for the throughput if:

	 * The value of the variable is computed considering, first, that

	 * idling is virtually always beneficial for the throughput if:

	 * (a) the device is not NCQ-capable, or

	 * (b) regardless of the presence of NCQ, the device is rotational

	 *     and the request pattern for bfqq is I/O-bound (possible

	 *     throughput losses caused by granting idling to seeky queues

	 *     are mitigated by the fact that, in all scenarios where

	 *     boosting throughput is the best thing to do, i.e., in all

	 *     symmetric scenarios, only a minimal idle time is allowed to

	 *     seeky queues).

	 *     and the request pattern for bfqq is I/O-bound and sequential.

	 *

	 * Secondly, and in contrast to the above item (b), idling an

	 * NCQ-capable flash-based device would not boost the

	 * throughput even with intense I/O; rather it would lower

	 * throughput even with sequential I/O; rather it would lower

	 * the throughput in proportion to how fast the device

	 * is. Accordingly, the next variable is true if any of the

	 * above conditions (a) and (b) is true, and, in particular,

	 * device.

	 */

	idling_boosts_thr = !bfqd->hw_tag ||

		(!blk_queue_nonrot(bfqd->queue) && bfq_bfqq_IO_bound(bfqq));

		(!blk_queue_nonrot(bfqd->queue) && bfq_bfqq_IO_bound(bfqq) &&

		 bfq_bfqq_idle_window(bfqq));

	/*

	 * The value of the next variable,